What Uses Less Gas - Coasting Or Engine Braking?
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- เผยแพร่เมื่อ 4 ต.ค. 2024
- Is It More Efficient To Coast In Neutral Or In Gear?
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What uses less gas? Coasting in neutral, or engine braking? Of course, the answer is it depends. A simple example? If you're approaching a red light, and know that it's going to remain red, engine braking will slow you down without using any fuel, and will be the most efficient option. If you know for a fact that the light is going to turn green before you reach it (which, you don't, but hypothetically), then it's more efficient to coast in neutral and maintain your speed, then get back on the accelerator once the light has turned green.
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Important Note: This video applies to *modern cars with electronic fuel injection* (gas, diesel, manual, automatic, DCT, CVT, etc). New cars sold today will all work like this (though there are always random exceptions). As you go back in model years, it will vary manufacturer to manufacturer which completely shut off fuel or continue to inject. Carbureted vehicles inject fuel based on vacuum levels of your engine, so this video does not apply. Sometimes I take pictures: instagram.com/engineeringexplained/
how does this work with automatics, wouldn't the torque converter not keep the engine rotating fast enough (requiring the engine to give it some fuel?)
So why does the new Mercedes E63 S cost in neutral to save gas?
Costs more for engine braking because it wears out transmissions faster. New transmissions have smaller parts so they don't last forever.
Capt Mifune, to stop the transmission from falling apart and dropping parts on the street? Many German cars have weak transmissions. They fall apart in intense driving conditions like in California.
I am curious dose this work with motorcycles also? I appreciate the videos always good information.
Cool! Now I can show this video to my friend who always insists on coasting in Neutral for every hill they encounter.
Bladed Angel oh hi! Love your channel
Totally foolish. Theyrr handi-capping themselves from control, should a swift emergency rxn be needed
Why do I see your comments everywhere?
Bladed Angel hello
Doing that right now, haha
When I'm trying to be fuel efficient (pretty much always), I simply avoid using the brakes. Avoid as much as possible (considering safety and road law, of course). Every use of brakes == throwing away kinetic energy that I needed to burn fuel to achieve in the first place. Of course, I apply the brakes when necessary and use engine braking, too (manual transmission) when appropriate or necessary. When coming to a potential stop, though, e.g. a red light that will turn green at some stage or stopped traffic up ahead that will start moving at some stage, the EARLIER you apply the brakes, the more likely that you will still have useful kinetic energy when you arrive at that point up ahead. If you rush towards a red light and come to a sudden stop there you will face the green light with zero speed. If you brake early / strongly enough, though, you can still have motion when arriving at the green light. That is a more efficient use of the energy derived from the fuel that you burned up in your engine. (We're talking very fine points, at this stage.) WARNING: It is quite dangerous to barrel through an intersection as soon as the light turns green, so don't do it. Some wiseguy might be running a red light across your direction of travel, hoping that he'll get through before you get to start but because you're so efficient, you both meet in a bloody, smoking mess of twisted metal in the middle of the intersection. Happens all the time. Drive efficiently, but drive DEFENSIVELY. Look in all directions before going through that green light.
I actually engine brake while also downshifting when I see a red light far ahead and by the time I get to the light it's green and I hit the gas in the appropriate gear. No wasted kinetic energy and saves gas because I didn't have to start moving from a dead stop.
@@TheBuddilla best thing to do is run stop signs and red lights to save gas
@@angelgjr1999 Been known to happen LOL
@@TheBuddilla "engine brake" is misleading because engine doesn't have brake lol... to slow down, the energy has to be converted to heat via friction unless you have magnetic conversion as in electric car to recharge battery. So when "engine brake", either the engine or tramission, or both, will take the friction to convert to heat to slow down. Anyway with the choice of tear/wear between braking pads and tranmission/engine, l choose the braking pads as they're cheap to replace by myself. I've been driving a 2010 VW Tiguan with 210k km, still on all original tranmission (only change trans oil every 50k km), change front braking pads every 2 yr, rear pads every 4yr, front rotor only once and original rear rotor. It costs about $60 for a pair of pads for front or rear, $2 for brake grease and 1hr DIY.
@@tonyvu2011 I know what engine braking is and it is caused by a vacuum, your engine is going to experience friction whether in gear or at idle while braking. It costs me much more to replace my front pads and rotors multiples times than to maintain the engine with proper oil and cooling. Of course I am running a highly modified boosted(supercharger) BRZ with upgraded brake system...
Another fuel saving tip: try not to stop. Starting from standing is a big fuel user overcoming rolling distance from standing. The answer is to slow down and keep crawling to traffic lights, through traffic queues, and so on - as long as it’s safe and legal to do so.
Tell that to the cops hiding round a bush at an empty 2 way stop when I roll the stop sign lol
@@cyandrix safe and legal ^^^
Downside is you need a lot of space ahead to roll, which most people will just see as 'free real estate' and merge in 😂
Basically, If you're going to stop at some point anyway, use gears.
If you are going to effectively use the bonus kinectic energy you get from neutral coasting (longer distances, climb up a cliff ahead) then it becomes viable
When you don't need it to stop you going 120 mph into the twisties, engine braking is just another loss - like rubbing brake braking, unused roof rack braking, or underinflated tire braking.
Basically, use gears.
@@dpgerarddp Unless you live in a hilly area when the alternative scenario is extremely common... or if your vehicle does NOT shut off the injectors when coasting.
but then again if you are going up a very steep hill, it safer to be in gear
Except that it's not very safe. Unless you're an a closed track that have been checked and secured for you, it's very unsafe to coast in neutral.
"The answer is always it depends" I love science xd
at least you are getting a correct answer, most people would suggest the method they use which might be incorrect
I think this sadly is the reason climate change hasn't been 'sold' very well by scientists. It's easy for a non expert to make a sweeping statement and say it's definitely not true, but a true scientist will never say it DEFINITELY is true. Although they are confident that human climate change is the least wrong answer, and therefore probably true, they won't commit as they keep an open mind. This keeps conspiracy alive!
Due to the amount of variables at play, this is approximately true, brah.
That's because truth is relative not absolute like the fairy tale books claim.
Valentyne S. umm. No. There are truths in the world that are absolute.
If I'm intentionally engine braking down a hill, I'll occasionally put the A/C on to get a little more braking. Kinda funny feeling the compressor cycle on/off also gives you a good idea of just how much power that little thing uses.
iVTECInside damn, never thought about using that, I might do that now on steep hills so I can use a higher gear
Good way to burn up your compressor clutch prematurely
that uses up the compressor clutch?
Not more than running the ac in any other condition.
I'm gonna try that
I've always wondered this... Thanks Jason!
I've always wondered this, now I know! Thanks man!
Just for you Matt! :)
Heyyyy Matt
RTFM
This was really helpful. I didn't realize that fuel wasn't being used when the engine brakes were revving high. Thanks for posting
FOR YEARS . . . I've been trying to get definitive answers on the MPG advantage/disadvantage of (manual transmission) neutral coasting vs engine coasting. Just couldn't find it. This pretty much answers the detailed concerns that I've had while trying to maximize fuel efficiency. It's the detailed explanations such as this that are important and don't get attention that are why i subscribed and love this channel. EE is the ish!
The short answer is that in a situation where engine braking would require you to use the gas pedal later (and coasting would avoid that), coasting is more fuel efficient. And in a situation where coasting would require you to use to use your brakes later, engine braking is more efficient.
Any time you use the brake, you loose energy in the form of heat to the environment. Ditto, any time you use the gas pedal, you ‘loose’ as much energy as the kinetic energy generated as heat to the environment, since combustion engines generally have an efficiency of less than 50%. Thus trying to control your speed by using both the brake and gas pedal as little as possible, is generally the most efficient way.
This can be compared to trying to control the temperature in your home by opening windows in summer during the night when it is colder outside and during early afternoon in spring and fall when it is warmer outside. Ditto for using window blinds in summer during the day to keep the heat out.
@@aphextwin5712 so inother words use gears
Few minutes ago I was just thinking about it while driving home. Arrived home and here's your video about it...
So nice!
thanks man, I've been coasting down this two mile hill in South Carolina in neutral forever. noticed difficulty in control, and braking falls through as well. Didn't know coasting did 99.9 mpg. I'll leave my gear box alone now bro! Thanks for the great vid, and as always, good luck on the next one!
I can't get enough of your coasting & engine braking videos. Thanks for anew one!
Short answer: In neutral the engine has to go bang to keep spinning, in gear the hill keeps the engine spinning. In modern EFI cars the ECU cuts fuel delivery when coasting in gear, results may vary.*
G.Masheen, I was a bit confused how a motor, accessories and such can work while no fuel is being injected; your statement is much better than how Jason explains it.
But is the fuel actually cut when coasting in gear? Cut to 0? Ie 0 fuel being used? Then engine us off? But no need to restart?
This seems contradictory.
the engine is not off, as it has contact and is spinning from this, instead of using fuel@@scartinojoseph1407
@@scartinojoseph1407yes, its cut to 0. its because since the engine is IN GEAR, while going downhill the car wheels are spinning, which spins the the gearbox, which spins the engine, and as long as you are going downhill at enough speed to keep engine above around 800rpm (idle rpm) there is no NEED for the engine to use fuel to run, because its BEING run by the car wheels. understand?
Driving a big rig... Use engine brakes to save BRAKES and lives lol.
Henry King it's more of not overheating brakes than saving them. Overheat them and you don't have any to stop the rig. With engine brake (retarder) you are able to travel faster down a hill than without, because of overheating the brakes.
MarioPL true overheat caused me to lose brakes on my old Eclipse GST back in the day.
+Henry King TFW you have it in just the right gear and engine brake setting and don't even have to touch the service brakes :D
No Georgia overdrive for me.
Ashton Pinch true I'm a Honda guy so I knew my gears better with my GSR. That Turbo Eclipse wasn't my preferred choice those gears were longer . Sold it lol went back to Honda Integra like I shoulda stayed with.
why there's a thunder in the picture
purified !! Weather can be unpredictable.
A thunder? Hmm I've never seen a thunder before
cumulonimbus*
For dramatic effect! :)
You dont see thunder, you hear thunder. You see lightning
wow that means by going down a hill you can use tha a/c for free
Free? You had to get up that hill in the first place right? There is no such thing as free energy.
Archer true but if you intend stopping at the bottom you might as well use it. It kind of is free if you were just going to brake and pay to use a bit more brake pad and disk.
Yeah, you shouldn't drive up hill and then same route back just to get "free" ac, but if you're driving up/downhill anyways, you might as well use ac while coasting
SakariNy Agreed. I you have to go over the hill anyway this A/C use is not using fuel. Assuming of course it didn't cut into the roller coaster scenario Jason brought up.
Free because you're not using the brakes as much is what he means.
It's awesome to see how much your channel has grown
I would say it depends too. I have a 97 Ford Escort and coasting definitely helps me save gas. It's hard to compare results because the efficiency of fuel management systems have changed dramatically within the last 20 years.
I love the rain cloud in the drawing.
Worth adding - depends on the engine too as carburated engines won't shut the fuel, I believe :)
I was going to ask if every fuel injected engine shuts off fuel.
Depends on implementation but it's generally true that carbs won't shut of fuel. -There are som oddballs out there :D About fuel injection. If it has mechanical fuel injection it will usually not turn of fuel. Most if not all electrical ones will tho
I thought this might be the case but then the question becomes "What Uses Less Gas with a carbureted engine - Coasting Or Engine Braking?" Probably the same because it just sits with the fuel system running minimum/idle amounts of fuel into the engine.
Then there's two-stroke engines. On some of them it's actually harmful to rev the engine without adding fuel since it needs the lubrication. Thankfully this is a thing from a very distant past lol
It's vacuum-driven so higher RPM = more fuel. :)
Worth noting that this function, "DFCO" is really available in fuel injected cars maybe past the early 90s. Also, one more thing to add to when you might want neutral is when you're going down a hill that's not steep enough to keep the car at a constant speed when you engine brake.
You're looking for a higher gear in that scenario, not neutral!
If you don't get enough speed in top gear, it's very likely that either:
A) you target high speeds that aren't safe to coast at
B) the decline isn't steep enough to accelerate you to the exact speed anyway, in which case it's more efficient to keep a constant speed with low throttle in high gear than to accelerate, coast, accelerate, just like on a level road.
@@LRM12o8with a higher gear comes a higher minimum speed
In certain inclines you either use the throttle or speed in a higher gear. I know that because I have a 100m or so straight nearby where I can't coast in 4th gear but if I go to neutral I only go down to about 30-35kph before it picks up speed again halfway through. 5th gear means throwing myself at a hairpin way too fast
More generally, if you need to slow down or use the brakes during the descent (for example coasting will cause you to exceed speed limit) or at the end of the descent (for example you reach an intersection) then better to leave in gear. If you need to maximise speed and will never have a requirement to slow down or use the brakes during or after the descent, then better to coast.
A different scenario is a hill that isn't steep enough to keep the car rolling at the desired speed with transmission engaged, but is steep enough to maintain speed when in neutral. Then I suspect "neutral" wins, and without exceeding the speed limit.
As a semitruck driver, I was surprised to see the latest Paccar 12-speed automatic transmission start shifting into neutral on downhill slopes. We were always taught not to do that while using manual transmission because it would prevent lubrication from being circulated (and is illegal -- "uncontrolled roll" they call it) but apparently they found a way to solve the problem of lubrication, while also getting the efficiency benefits of free wheeling.
Efficiency counts not only the fuel consumed, but also the brake pads and brake rotors which wear out much faster if you coast in neutral compared to engine braking.
that's why you don't brake when coasting
I always thought neutral was more efficient so I always coasted down hills because it made me feel better. Now that I know this, I think I'll use engine braking more. It's all a small difference in a Miata like mine but it's still interesting.
If you have an old enough Miata, it might not turn off the injectors during coasting. You can check it with a scan tool or some code readers.
coasting also wears out your brakes very fast
@@marrox013Use engine braking where coasting would force you to use your brakes, use coasting if engine braking would require you to use the gas pedal (both rules refer to the stretch of road for which you can predict things like gradient and speed requirements). The video only pointed the latter aspect, but those two go together.
@@aphextwin5712 yeah, that's what I meant
@@marrox013 Coasting does not wear out the brakes, provided you plan and do not get into a situation which requires you to reduce your kinetic energy. If you have a downhill down to a bend, you use the minimum of engine braking needed to enter the bend with a manageable speed.
Great video, had this discussion at work many times too. The built in mpg gauge may behave differently based on manufacturer software. I logged injector duty cycle on my Subaru to get the same conclusion and would be more consistent data regardless of the car.
Sometimes its just a real time reading instead of an "average"
I’ve wondered this since high school when my friend used to do this every hill... but I never got around to looking it up haha, good vid
it is most effective if you use both. especially if you know the road well. I use neutral on the hill when I want to gain momentum and continue moving on the flat road as long as possible without adding gas.
Thanks for the video I no longer coast downhill. Coming back to your scenario it would probably be more efficient even if there are not a series of his but flat straight road as the momentum built by coasting can be used to cover some distance as long as you don't exceed the safe speed for that road.
Nice technical tidbit here, but I, personally, never go "out of gear" for any reason. I really wouldn't drive a car where I was worried about mileage. At least- to that level..... coasting... really ? But I do get the point and appreciate the educational aspect of this post. I just prefer to always have instant access to power, in case...
In case of what?
Lots of things, really, where you need instant power. If you are "in gear" and engine braking, you know it's going to be there. Like for instance, coming into a corner a bit too hot and knowing you will need a gob of power- to get, perhaps a drift going. I wouldn't want to be in neutral and suddenly have to grab the shifter and pray I am in an RPM range that will get me the power I need. If I'm engine braking, that power is already there. I typically keep engine braking RPM around 4,000, which works fine in my car- right near maximum torque.
Rick Noah that's why I love EVs!
MercedesAMGsRULE
You've got me there !!! Totally agree and am hoping that- 1) the 'possible' VW Beetle EV is awesome and- 2) I can afford it !
I just have a thing for VW's... driving my 7th now.
^THIS. Only relevant question when you need to decide between coasting or staying in gear.
Great vid and explanation. You should do a vid debunking the myth of "engine compression braking" and show how the engine really has very low compression with throttle plate closed and coasting. Perhaps get into pumping losses and why cylinder deactivation works by opening the throttle further but indeed still uses the same amount of fuel at the same rpm as if it was running all the cylinders. Might be a good topic :)
-Eric O.
South Main Auto Repair I like this idea, might you want to do such a video yourself as well? Love your channel!
Thanks man! I think it is a good topic for this channel. Just always find it funny when people say they "compression brake" when the engine has less than 20psi compression during a deceleration event... 90% of mechanics out there have no idea it is the throttle suction that is causing the engine braking.
Maybe they all drive diesels.
'Engine braking' is something of a misnomer really. When you lift off and enter overrun conditions there is actually a lot more than just the engine slowing the car down. For example, aerodynamic drag, tyre rolling resistance, rolling resistance of bearings and permanently connected transmission components, brake pad drag.
Even the engine's contribution to the total 'braking' effort is made up of many parts - 1. internal friction and 2. pumping losses (primarily intake vacuum, not compression as you say), 3. alternator load, 4. water pump load, 5. aircon load (compressor).
Could probably write a book!!
That would be interesting!!!! Have a kill switch for ur injectors so when u engine brake u can go wot and really start engine braking lol
Jason, great points. Glad you addressed this. Many factors are involved but I feel you addressed it well. Thank you.
In summary: coast in gear uses no fuel, but the friction in your powertrain slows down the car faster than coasting not in gear. Coasting not in gear uses some fuel, but the car does not slow down as much as you would in gear, so you can travel further without stepping on the gas again.
What if you simply coast with the clutch pressed? Is that the same as idling in neutral?
@@caracaes that's the best way to destroy your clutch
Coast in gear slows down the car faster than coasting in gear. What??
@@caracaes Yes
@@MrQuay03 Thanks. I have edited my comment.
can you make a video about the latest inventions in automobile industry for the past 5 years
It took me a long time to get used to this when I bought a newer modern truck... If I touch the brake even for a second it downshifts and starts to engine brake to slow me down even after I let off the brake.
My brother’s Toyota Tacoma does that when going down a steep hill. It scares me because it reves up the engine really high, makes me think it’s going to explode. Also it shows worse current mpg
Search if there's a 'hold' button.
Finally a video about this, its always depends on the scenario!
Never seen so many experts and specialists in one place at once
Long story short in older cars (carbureted & earlier EFI) cars coasting is more efficient because it doosen't shut off fuel, in modern EFI cars engine braking is more efficient because the ECU will shut off fuel. Better answer than 'it depends'? XD
Armour Shooter what do you mean by earlier efi? Im curious cause my car is produced in 2001 and i wanna know because im engine braking everywhere😂
Armour Shooter i think marc’s question was how can he determine if his car (a 2001 model) has ‘modern’ efi or ‘early’ efi technology
RJ J oh mb, best way is to do some research on the current model. im not an expert so this is the only advice i can give
80s - early 90s
I agree, was thinking the same thing while watching the video
"Ignoring all the negative consequences of doing either of these. Whichever one's safer, that isn't the place for that discussion"
Oh?! Then the most efficient is the car in neutral with the engine off. You'll get downhill pretty fast and spend 0 gas.
ROUGHLY SPEAKING
Arkaid D GG brake pads
As he shows in the video, you also spend 0 gas with the vehicle in gear without turning the engine off.
@@joemilton7552 but you gotta turn it on
@@isitmichaelormicheal1263 it's already on, you'd have to turn it off for it to be off, then turn it back on again, not to mention your brakes and steering won't work right with the car off.
Three scenarios where I can confirm by myself that this is true:
1) I've done the example used by Jason of reading the km/L showed by the car's computer by costing and in gear, BUT with the A/C on and fucusing when the compressor is on and off. So, when I'm in neutral and the compressor kicks in, the km/L drops dramatically. For example, when I'm doing 70km/h and reading +50km/L and the compressor kicks in, the km/L drops to about 20-25km/L and when it shuts off, it gets back to +50km/L. Now, when I'm in gear, the km/L literally never moves and stays in +50. I need to be going really slowly (below 30km/h) to start it dropping.
2) In the particular case of my car, a Suzuki Swift 2018 1.2L, you can feel this cut off of gas. If you're slowing down in gear and you get near 1200-1100rpm, you feel a gentle acceleration. Likewise, when you're speeding up and the engine pass that threshold, you can feel how it no longer accelerates.
3) I was a "coast in neutral" guy. Doing so, I got about 16-17 km/L off my Swift. Then, after I noticed the second scenario and watched the previous video, I started coasting in gear and now I'm getting 17-18 and funny enough, when I use the A/C, sometimes I get 19 in city ☺️
I tested everything regarding car coasting. And here's what i found: I have an automatic sports car and according to my trials and the fuel economy meter, putting the car in N or D makes NO difference in fuel consumption while the car is moving as long as your foot is not touching the gas pedal. But if the car is stationary, idling (stopping) in N will decrease your fuel economy. But putting the car at N and removing your foot from the gas will help the car glide smoother and for longer distances, therefore reducing the need to step on the gas which will make difference in your fuel economy. Consider it a skill to know how to coast the right way. Hope i helped you guys.
that right there is why I love manual transmissions. the control they give u over ur own car is unbeatable.
But everything here can be done with most autos, including my 2000 BMW. Not saying manuals aren't great but nothing in this video can't be done with an auto
But did you account for that thundercloud near the bottom?
My man Jason is trending 😏🤑
As much as I love these science videos, we need more s2k content!
Coming very soon, probably this Wednesday!
I use to think about this all the time. great video
I just love how you answer questions I didn't even know I wanted answered
A caveat here: Fueling GENERALLY only cuts in the top 2/3 of the rev range. In the bottom 1/3, fueling will cut back on, which is why you'll get some gurgles towards the bottom of the rev range. So if you leave in high gear, you won't see as big a difference as when by putting it in a lower gear. Which also means you need to underline rev matching. Rev matching uses fuel. WAY more than you're going to save. So you'd have to granny shift it to see any benefit. Granny shifts wear out your trans. Transmissions are way more expensive than gasoline. But the easiest thing of all to replace (besides gasoline) is the brake pads. So you kinda have to decide what your maintenance strategy is and go with it.
tailgating a semi gives you the best fuel economy LMAO!
Jake Maningding lol I use to draft off semis in my 3cylinder Daihatsu just to be able to maintain high way speed.
Always had this question in my mind. But wait, if the engine RPM is more than idle RPM (cuz of downhill), it doesn't inject fuel, but when it's at idle(neutral), it starts injecting?? Is that what it is?
Sanderen X Yes
Yes, in one the engine turns fast because the wheels turn fast, because the wheels are connected to the ground AND connected to the transmission/engine, in the other the engine is not connected to the transmission so it's consuming fuel.
coscorrodrift Thanks. So the ECU senses it and makes the decision to stop injecting, I presume?
Sanderen X yeah, it sees that you are applying 0% throttle with the TPS or gas pedal sensor and stops injecting, this is how engine braking works
The Real Santa Claus That makes sense. Damn I knew this when I was in college. I'm forgetting things 😅😅
Finally an analysis that takes subsequent hills into account. I live outside of Denver and have been dropping 3,000 ft down I-70 every day for 25 years. Most of the time it’s been in the same car! Due to this specific terrain the best is a hybrid approach. Leave it in gear until approaching “Dead man’s curve” then go to neutral to build up an illegal amount of speed to coast over the long small hill with reasonable speed before the final drop. Stay in neutral to allow for the farthest coast once you hit the flats in town.
Don’t do this in a big rig though. Always stay in gear. At least once a week there is a rig on the side of the road with its brakes on fire, and several times a year the flames take out the whole truck!
Now I have an electric car which takes all the mental gymnastics out of the drive. Set it and forget it.
Engine braking FTW! My instructor told me to always use engine braking when possible. If you're just coasting the vehicle tends to accelerate when the hill get steeper and it quickly becomes unpredictable. With engine braking you are able to maintain constant speed more precisely and your driving is safer and smooth.
Even given the limits of this discussion, it was about fuel efficiency. There are other things to consider, like, would you rather wear out your brakes or your engine?
i think you have to know the roads , to decide if you coast or leave in gear. when i know the roads i would prefer to coast in a higher speed. but in unknown roads i would prefer to hold the gear , cuz its much slower
Engine brake, because i notice the engine cooling off when engine braking down long stretches, meaning no combustion to generate heat
high rpm engine = high rpm on the water pump
Georgi Popov not really , just the normal 3-4 k revs
Stuck open thermostat
If you leave it in neutral down hill it will get cooler
BO4wd yes it will.
Instead of putting it in neutral in the hill scenario, why not just change to a very high gear (like 5th or 6th)? You'll still be in gear but the engine braking will be almost none.
Try it out in your car. There's a significant difference. Especially noticeable once the road starts to get flatter.
I don't really think that's any better. If you're in a high gear and going slow (while momentum builds up) you still have significantly reduced control of the car than if you were in an appropriate gear for the speed.
My Car is around 3000 rpm in the highest gear at 120km/h it is a huge difference to shift to neutral. I have to stay on the accelerator to hold the speed downhill. I i shift to neutral i can just roll down the hill and the car will accelerate
@Engineering Explained, engine braking is the lowest when engine RPM is low, and low RPM is what you expect to happen when you use high gears ( 5th or 6th).
Congratulations on your Engagement!
You should have shown a engine ecu fuel map table live, you can see when using engine braking it goes into the far left lowest value, whereas in neutral it just sits at idle (which has a higher value than engine braking)
It would be interesting if you could do a test run of that hill, or a different one, where you go down once coasting and once with engine braking, always at the same speed ~30mph and see what is the difference between the two. While you are using engine brake there are times that you need to use the gas pedal and that lowers you MPG to 20-30-ish while when coasting at a stable 30mph it will stay at 80mpg... It would be interesting to see what is the most efficient average =)
80 sounds awfully low coasting down a hill lol
Hey EngineeringExplained, this picked up my exact question from a videos back. But I have to ask something more: If there is no hill - so just a horizontal piece of road - what is more efficient? You don't roll as far, but you dont use fuel - or you roll further, but keep your engine idling. Any idea in this scenario?
I'm pretty sure it's fully dependent on the car. The rolling resistance, wind resistance inertia, compression ratio, gear ratios, idle fuel consumption all comes into play when figuring that out. I'm willing to bet a lot of cars are more fuel efficient coasting and a lot of them aren't.
Depends on the distance covered at speeds low enough for neutral to inject fuel. Not really a scenario where you should be doing either blindly
Stay in gear. Your 100% of the time using fuel to keep your engine idling while coasting. But even backing off the throttle in gear will stop using fuel in small scenarios. Plus engine braking greatly reduces wear on the brakes, more control over the vehicle, and short breaking distances. More pros than cons
Edit: throw into the mix that a lot of cars has cylinder shut off too now. So you may be running on 2/3 cylinders (depending on engine configuration) but you’ll be idling on all cylinders as they don’t cylinder shutoff on idle.
Engine-off neutral coasting 😈
And then the steering lock kicks in while u r turning
@@hussnainsamee2603 lol true. My car stalled out once while I was exiting a highway. Steering locked and I almost shat myself. No idea how my car stalled first and only time it randomly shut off young 45 mph.
My grandpa used to do that a lot in his old Skoda. It didn't have power steering so he had no power steering to lose
My jeep Patriot reads MPG forever. On a loooong downhill desert gravel road run, I shut off the engine and kept it in neutral. What a hoot to see 2,200 MPG on the dash! Just imitating a Prius, Polish style.
I manly clicked on this video to support you, i already knew the answer (more or less) but were i live only staying in gear will allow you to save gas.
Have a good night (morning in the us)
Hi EE, loved your videos! Been watching them all the time. I have a question regarding rev-matching and throttle blipping. I found it easier to blip and rev-match a petrol-powered car than a diesel-powered ones.
I know that diesel engines generally have more torque at low-end and use higher compression ratio than petrol engines. In those senses, what makes the diesel engine 'lazier' to rev and petrol engine 'more eager' to do so?
I have found it equally easy (or difficult) to rev-match when changing gear, for either petrol or diesel. What makes the biggest difference is not the engine but the gearbox. My Peugeot has always been more forgiving of slight mismatch when gradually increasing/decreasing the revs until the gear slips in, compaed with my wife's Honda. The Peugeot has now done 190,000 miles so I imagine there's a bit more wear on the synchromesh that makes it more forgiving, but this was true even at 18,000 miles when I bought the car.
I find as a very rough estimate, in my car I need to increase or decrease the engine speed by *about* 500 rpm when going from one gear to the next higher or lower gear. *Any* change in the correct direction will be a bonus, compared with a) keeping the engine revs constant, or b) returning the engine to idling speed and then letting the clutch up on an idling engine (!!!!). I did actually get a lift with a person who did the latter. It was a difficult situation because she was my boss. Should I offer her advice? When she actually apologised for a particularly jerky gearchange, I very tentatively suggested that there might be a different way that would make her gearchanges smoother. Apparently her instructor had taught her to let the clutch up on an idling engine, and no-one had every told her about rev-matching. When she tried it and found how much smoother the gearchanges were, she said "I'll murder that driving instructor!" She still lifted her clutch foot right off the floor, rather than pivoting on her heel, but that may have been because of the size of her feet in relation to the position of hte clutch pedal off the floor. She was about 5'3", driving a VW Jetta, so maybe she needed the seat that bit closer and also her feet weren't as long as mine; I've never found a car where I have to lift my heel off the floor to let the clutch right in - even on my Pug which has a high bite point becaue the clutch has used up all its auto-adjustment range (though 190,000 miles on its original clurch is pretty damn good compared with previous cars I've had).
Having a rev counter makes it easier to rev-match than when you are having to rely on engine note to judge the correct speed for the new gear.
Do all EFI cars cut fuel while engine braking? Regardless of the year it was made
yes all, efi was universal in all new engineered engines since 80'
No. it's a rather new feature. My 2007 Pontiac doesn't and neither does my 1990 f150, but most engines within the last few years do.
Robert Short Pontiac doesn't exist anymore for a reason.
I don't think that is why though ;)
It depends. My Scooter doesnt cut off fuel while Cold and rolling downhill and also around 2000 rpms where it expects to detach the flyclutch so the engine doesnt stall while rolling to a stop.
No whiteboard math to support it? How can we believe you? We've come to learn that when something is true, you show us on a whiteboard.
My son had the same question. His 2015 patriot is a manual and I put in a odb2 monitor that showed gallons per hour usage. Going down a big hill in the Sierra - idle/neutral was 0.38 gph and in 5th gear at 65mph it was 0.54. So coasting in neutral was much better. Dangerous and don't try that at home but it's the answer we got. I didn't think it would be that high since the injectors should be shut off but apparently they aren't really 'shut-off', otherwise the engine would be the same as the key off.
I think neutral saves gas on flat level ground because leaving it in gear slows the vehicle down so much. Neutral means you should be able to coast much farther.
So could you do a video about using the tow/haul mode in an unloaded truck vs. using the standard transmission mode for efficiency? I was told that the transmission will shift less often in T/H therefore reducing fuel consumption, but I thought the standard mode was programmed to always find the most efficient gear to be in, even if it has to hunt gears more often.
So why are there signs posted in my state that say "no engine brake"
They are for trucks. Jake Brakes are pretty loud, and in cities or suburbs where braking is common, They don't want trunk drivers using them.
because trucks have a special engine brake, that close the exhaust valve, increase a lot engine brake compared to cars or light duty trucks but is noticeably loud so is banned in towns
It doesn't actually mean "engine braking is prohibited." It means "unmuffled compression release engine retarders are prohibited".
Mark Spelman you don’t know the purpose of road signs?
How does the engine know to shut off fuel when coasting in gear? Wouldn’t it be the same as just idling in neutral? Unless the speed sensor is at work? Confused on that bit
It knows because you took the foot off the accelerator. That means no more fuel injection, except when the engine rpm drops below idle rpm, then it injects enough fuel to maintain idling.
Event Horizon But how does it know? Which sensor/s is it going off of? And does this apply to all manual cars? Or just newer ones
mrsemifixit If it is above idle speed it shuts off. When your RPMs were to drop below idle speed it starts injecting again, to keep RPMs up.
Stefan S Nope, for example there is the engine speed sensor. Without that the engine speed would drop below neutral because the ECU wouldn't know it has to inject fuel now.
There are several possible sensors an ECU could use to work out if it's necessary to inject fuel into the cylinders or not. Like camshaft and crankshaft sensors, gearbox speed sensor and at a push you could theoretically use wheel speed sensors too as long as the ECU knows what gear the vehicle's in (though wouldn't be ideal). As long as the ECU knows the engine speed is above idle then it knows it doesn't need to inject any fuel.
Thank you. You clarified that issue for me . I used to coast in neutral on a manual transmission car. As I saw the revs going to a low number, as opposed to having the gears engaged would show higher revolutions. I thought those revs were coming from the engine burning fuel. Now I know they are just from the engine being engaged.
My wife does the same. I will let her know.
Thanks.
In Germany this is taught as basic knowledge in driving school.
Driver's education in America (and much of the rest of the world) continues to baffle and disappoint me...
Yo man loved you in that GMC Acadia commercial, no joke I love to see my favorite content creators getting recognized by big brands, keep up the good work with any luck you'll big super big in no time, the quality of your videos is already there so I know the audience will come.
Novice petrol head comments in 3, 2, 1...
Hondurr
Since you said petrol head I'm guessing you're on the other side of a large body of water...
In which case I have to complain about how you say Nissan. You're doing it wrong.
Don b What Nissan
Brits also can't pronounce Chevrolet correctly, they always say Opel.
Buddy Clem no your still not saying it right, you have to roll the tongue in Australia, "Holden"
So if i want to break, i use engine breaking.
mhm
SteelVsMetal No, you use engine braking - not engine breaking
SteelVsMetal if you want to maintain a speed downhill without going over and applying foot brake then yes, use engine brake. You still need to use the brake pedal to stop.
Like I said. Yeah, use engine braking when you want to brake.
so if i want to use engine **breaking** it will break my engine
At Subaru 99.9 means 0
that's why L/100km is better, 0L/100km means 0
Tony x, I would say, L/hectoclick is useful for calculating how many litres of fuel you need for a road trip. km/l is useful for calculating how long your tank will last with a known number of litres.
ok but L/100 is more precise, on my car for example lowest indicated consumption in km/l is 30 but lowest indicated consumption in L/100km is 0.0
It doesn’t mean 0, since it is number of miles per gallon; and outside hybrids, cars don’t need the extra significant digit as most cars under most conditions just can’t reach triple digit figures with any consistency. What is weird though, is some cars have it cap at 120 mpg, iirc my 05 civic hybrid did just that; now that is a programmer/engineering decision for whatever reason.
So for the most part, 99.9 with fuel cut = unlimited (miles per unit fuel consumed) - because infinity is a concept, not an actual number, you can trend to it, but in concept you have infinities that are greater than others, so it could never have a single value anyway.
Now, working at a dealership, I’ve seen a car read 0 mpg under acceleration; hummer h2, it had single digit averages for tanks in the 4-9 mpg range and the brakes felt like you were driving an overloaded semi, panic stopping because of idiots in front of you was scary, I had to drive it in town a couple times for them and I couldn’t figure out why someone would buy one after taking a test drive, expensive and dangerous for the street.
Useful knowledge, glad somebody did a video on it to help educate people.
Most energy efficient way: neutral, turn engine off (careful, depening on how your main braking system works you'll have to restart the engine before braking after a few times)
If you need to loose speed, then use engine braking. Same if you need the engine for the brakes, air conditioning or excessive use of electrical systems.
Just go neutral, then you just need to replace brakes more often !-_•
just use reverse. i dare ya
If you are a typical lazy fanatic that drives automatic you can, since they have so modern ECU's they wont switch your gear to reverse even if you move the shifter to R. However, i double dare you. Try it on a manual. *and say good bye to your transmisson :)*
The TeddyBear I tried this in my old corolla manual to prove a point to a friend. The gear for reverse is cut the opposite direct, you could be going walking speed and try to put it in reverse, it will just give you a high pitch grind. Also look up myth busters, they tried it also.
Not first
Same i guess lmao
Just use 5th if you want to simulate the effect of neutral (or 4th depending on your speed)
Reza Grans he meant first comment lol
Me too!
Last.
(For now.)
I have been wondering this for so long. Thank you for your help!
I read an old article about economical driving competition. Both were driving petrol 2015 Mazda, one was using neutral coasting (also using engine braking some cases), one was not using neutral coasting. Neutral coaster won the competition by over 0.1L/100Km.
Engine breaking of course. Coasting down hills in neutral is illegal in california.
seems like breathing is illegal in califuckingfornia
Well yeah obviously your polluting the atmosphere with CO2
Well giving someone aids is just a misdemeanor now
7evenb smfh
It is illegal to let a vehicle coast freely downhill in neutral in many states. The way the laws can state that the vehicle coasting downhill in neutral the driver doesn't not have control of the vehicle.
Nice answer - knew this one but you do a great job explaining it as well.
I've wondered about this so many times glad to finally know the answer.
I would like to generalize Jason's point here. The goal of coasting in neutral is to conserve your vehicle speed (momentum). Even you don't have another small hill to climb, but have another 500 ft to a stop. It is more fuel efficient to coast in neutral first, rather than to coast in gear, and find that your car has slowed down too much and you have to accelerate again.
Dude this is crazy I was legit just wondering this exact question last night on my drive home and I came to a similar conclusion. Thanks for the confirmation!
I do the following with a manual transmission. If I need the car to continue rolling and there is no stop or speed limit I coast by pressing the clutch. If I need to stop or respect the speed limit I use the engine break as much as possible before using the breaks. To really save fuel using engine break the driver needs to think always what comes ahead. Most modern cars with automatic transmission and CVT also use a mild engine break when lightly pressing the breaks but the driver needs to anticipate stops and be pacient. In a manual transmission, engine break in a lower gear is also very nice before turning at high speed.
Nice explanation.
So basically if you have hill to climb after the down-slope, then put it in neutral. Otherwise, use engine braking.
i agree with this. my grandpa always taught me that acceleration is the largest use of fuel especially from a complete stop. neutral if its a long hill and safe to do so, engine brake to help stop if its a stop sign comin up. of course, he wasnt used to fuel injection. he was still right
Great. Just a got a new car and wondered why it maxed out on fuel usage when I took my foot off, you explained that. Thanks
That road reminds me of the trip down from Hurricane Ridge in Olympic National Park.
well edited video, as usual
What I have observed is coasting in gear is going to stop you quicker than in neutral if you are in a plane road, not steeped hill, and in that case it might be more fuel efficient to coast in neutral as you will be able to coast for longer. However, it is unsafe and illegal in some states like Tx. You can do that in a manual transmission car, though, by pressing the clutch pedal.
On a manual,sometimes i coast with the engine shut off when it's a long downhill and it takes like 6 miles till i will need the engine again. I just make sure the key is turned to the ON position to avoid steering wheel lock and to be able to bump start it,and the vacuum brake booster has a charge,if i brake like twice i bump start the engine to charge the booster and i shut it off again. Not practical but it's fun,the only problem is you don't save fuel unless you wont go uphill again,you might go down for free or less but going up takes let's say twice the come and go on a straight road.
Next thing i want to try is to coast downhill with the engine shut off and a gear engaged!
Easiest way to explain is that you have a certain amount of energy when you are on a hill and that keeping the engine at a certain RPM(idle, 800rpm) requires a set amount of energy. Coasting or energy braking use different methods of keeping the engine running but end result would be about the same. The difference being friction. You have air resistance as well as mechanical resistance inside the engine and transmission. When coasting, you are traveling slightly faster which would mean more aerodynamic drag than engine braking but engine braking means engine is spinning faster than idle as well as the transmission being spun.
When engine braking, you aren't using fuel to power the engine, you are using the speed from the car that stemmed from fuel, and slowing down the car in the process which then later requires the same amount of fuel to accelerate. I would just use the safest or most practical method. However, because there are special scenarios where one could be more efficient than the other, there is no definite answer.
Good recommended video choice.
Even without being in neutral, my old T-bird had a four speed automatic, and the fourth gear was an overdrive. When it was in that last gear, it would eagerly roll downhill, and it would pick up a lot of speed, without my foot on the pedal. My Honda SUV, which weighs a lot more will adjust the transmission, to keep it from going too fast, downhill. In fact, it caps the downhill speed at around 40 or so, whereas the T-bird could get above 50 on a good hill. When the speed limit is well above 40, then you are definitely using more fuel, because you have to keep on the pedal to maintain your speed.