Why Cyl #4 Overheats on Subaru EJ-Series Engines
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- เผยแพร่เมื่อ 1 ต.ค. 2024
- This Subaru DiY video dives into why cylinder #4 overheats in Subaru EJ-series engines. This is a common issue that often leads to preignition and internal damage. This video is the fourth video in a series on coolant flow through Subaru EJ-series engines and why you should consider installing a ‘reverse coolant' (aka 'coolant balance') modification kit.
This video is part of a "Build Series" (see "Playlists" tab for all videos) for my 1998 Rally Blue Pearl RSTi Coupe (Impreza 2.5RS swapped with a EJ205 turbo engine), which is 1 of only 720 sold in the USDM for 1998. This RSTi Build has come a long way and includes a full archive of videos documenting how to: (1) Pull a EJ-series turbo engine, (2) Replace the head gaskets, (3) Add key upgrades to increase long-term reliability, and (4) Restore the interior to OEM specifications.
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When you have symmetrical AWD, you gotta balance that with some asymmetrical exhaust headers.
YES! Exactly - thanks and sorry for the late reply!
well STI has assymetrical awd #iamboringatparties
What about the H6 or the Porsche configuration?
Great information! I didn't know the ports were placed like that.
Like you said, it inspires me want to make a custom performance head. What other things would you change on a newly designed head? (like direct injection, more space for larger cam lobes)
And I wonder if this extra heat in the head is a contributing factor to head gasket failures?
Just purchased a 2021 STI and was told about a mod on cylinder #4 and asked to watch this video. First ever STI and trying to learn more. Coming from a six year WRX driver.
Nice. It’s a good mod for sure. Lots of new STI owners use it.
I think you have good points about heat transfer to the wall of the cylinder heads. I also believe the main reason that no. 4 has more of an issue is the coolant flow. No. 3 has the benefit of the coolant return from the turbo. No. 1 doesn't have the problems because of the coolant flow path and some heat transfer from the flow of air from the radiator fan
Good point buddy! Totally agree. Cheers!
Interesting point! Anyone else notice that early head-gasket leaks seem to occur most at.... Cylinders 1 & 4?
Cyl #4 is always the one that loses compression on ej257's that I've worked on.
I keep running across your channel I have to give you your props I love it. I like to work on my two subaru' 07 Sti and 06 2.5I lol I have a thing for the GD Hawkeye gen. But today's video is very informative and totally makes sense. Looking forward to some more great videos as I'm looking to expand my knowledge with these engines.
Sweet rides! 07 sti is a bit unique with it's "v" head castings.
my fully rebuilt heads on a brand new block = after 4,000klm i fitted the number 4 water by-pass kit = instant differance - and it is winter now = really worth it !
Interesting theory, but why doesn't the 1st cylinder have the same issues with temps as the 4th one? The exhaust ports on them have the same layout.
It’s because that side sees cooler temps because there is an addition path for coolant to flow. He mentioned it but didn’t go to detail in this video. The 4th cyl doesn’t have that additional coolant path unless you do the cyl 4 cooling mod
I see people talking about cylinder # 4 all the time. But I had an 06 WRX with 190,000 miles on the original short block and it’s still going down the road with the next owner. So I wonder why there’s so many complaints.
Lots of tuners see issues with increased cylinder pressures.
Awesome video tons of info love your channel keep it up!🤘🏻
Cylinder 4 cooling mod?
I want proof that it helps. I hear conflicting reports.
What could be done to reduce block and head flex when hot thus compromising head gasket seL integrity?
check out subi-performance, that guys is milling grooves on top of the cylinder and imbedding copper wires in it help HG sealing.
Luke, you kinda remind me of the mad scientist off Fast and the Furious. Making me think of shit I never thought about. Good insight.
Thanks. I like getting people thinking. 😁
Extremely interesting, I have a question, on idle is it normal to have the right side of the exhaust to get heat up faster than the left. I have a 2008 subaru wrxsti.
So wouldn't cylinder one have heating issues too ? If it's designed the same. Or does it have better coolant flow than #4?
Great question man!!! It doesn’t have the same issues, but you’re on the right track thinking it should. I think the reason it doesn’t is due to the timing maps used, they use cyl 4 to to determine where the limit is for timing advance by having a bit more advance for that cyl compared to others. Plus, I think the coolant enters from the from have of the short block which may create better for for cyl 1 vs cyl 4, even though the exhaust port path is compromised for both cylinders. Hope that makes sense, cheers man!!! Greet question too!!!
@@SubaruONLY It's also at the front of the engine where cool air is constantly circulating, but the back two cylinders up against the firewall definitely live in a hotter place to begin with.
Would be good to remake some heads out of billet
You are truly one of the best DIY channels!💪
Well that’s a hell of a complement - thank you big time!!! 👍
... If not designed right down the middle of each cylinder, but even moved closer to the middle of the two cylinders so the flow is the same, with the same deviations into the manifold to keep the manifold pipes close together. Air in, air out, as smooth and as fast as possible should be the goal. Yes?
Yep. Pretty much! 🤙
Why does he only say right turns when clearly cylinder one is making a left turn out, same thing with the other side. I get what he’s getting at but two rights just make a 180 degree turn back into the engine 🙄
Hmm. I’ll have to take a closer look, maybe I mis-spoke…. Thanks for the comment, cheers!
Do you always wear sunglasses due to the kinetic energy your eyes emit?
interesting theory Luke. I appreciate your thoughtfulness
Looks like your eyebrow is making a rightbangle above your sunshades
lol...
Is this a problem with the FA or 3.6R engines?
Not sure tbh. Don’t have much experience with those engines.
Ever had any problems with coolant flow after installing this mod? Ever since mine was installed, by a Subaru specialist shop, I’ve had problems with overheating at the track. And when I turn the heat on full blast it’s blowing cool air. I’ve burped the system several times but still seems like coolants not flowing as it should.
Haven’t heard of this happening, it does sound like something is wrong. I’d double check the routing or maybe even remove it.
Probably still has air trapped in the system. Lots of channels report the STI is extremely hard to purge. I think we have to go with a pressurized coolant refill system to force the air out. The flatirons racing channel is currently dealing with this issue.
Of course it's a trade off, The developer never thought people today are pushing 400whp on this thing. The rally 22b only has 345hp and longevity of that engine is not a concern. EJ20 is pretty much designed as a 200hp engine.
Ej have no problem with overheat 4th cyl, thay have problem with deformatoion.
Hmm. I’m listening - how so? And what causes it?
@@SubaruONLY rotation moments adds from each cylinder and accumulate near 4th cylinder.
#4 generally gets less oil pressure in it as well with the stock oil pump ... and the stock fuel system may contribute to it as well ... I tend to protect number #3 more because of the turbo but #4 does seem to be more of an issue due to heat/oil pressure.
Is this issue is equally relevant for ALL revisions of EJ20 EJ25?
Very well explained, you should hashtag STi, wrx, subaru engineers
So if we build an ej engine and cylinder heads, we should most likely get our heads ported and better heated treated intake&exhaust vavles. Makes sense that way heat can flow out better
Is there any room at all for a bit of a port job per say? Is there enough material to try to somewhat round that corner anymore without getting into or compromising the coolant jacket? I know its like a 99% chance youve already thought of this because you obviously know what youre doing lol but i figured hey you never know.
Having 2 exhaust ports that close surely creates a hot spot. Can't be good for the metal in the long term...
That makes sense but theres more. Subaru made cyl #4 run hotter by giving the head less coolant flow and less fuel, since the knock sensor is located closest to cyl #4 , that cylinder's knock will be detected more. So other cylinders being cooler will have less knock by nature. Subaru fixed this issue with their FA engines by giving it 2 knock sensors. But no worries for those EJ25 owners, theres a fix for cyl #4 to run cooler, i will be making a video on it in a few weeks, I just had my lucky #4 crack on me during a trackday session. Also Subaru been using pistons that have more silicon then usual, that makes the piston hard but brittle, those pistons dont expand as much as say forged pistons, a lot less actually so subaru can go for tight clearances to avoid piston slap when cold, but they crack when beat on, mine went at 37K miles. check out my last video. Cheers boys! Subscribed! great channel, thanks!
how does it have less fuel lol? makes no sense.
Do you know if the SOHC heads have the same issue with #4. I was trying to figure out if I need/want the coolant mod on my supercharged 253.
that is why i left ej and slam in to iron block 4g hihi..
Great channel and content. where are you located I want to bring my Subi to you to work on.
Does this also affect single port ej22e engines too?
Late model engines have all 4 or even 6 or 8 all going into 1 single exhaust port 🙈
Hey bro, I have a 1997 impreza uk turbo which is overheating but only when on boost, leaks coolant from the overflow tank, would this always be headgasket? What checks could I do? Thank you for any response.
Yes, very possible it could be the head gasket. Can use a solution to test the gases in the coolant for combustion by-products.
Everyone could use the 4th Cylinder Cooling Mod that Dom makes. This flaw is big and the mod resolves a lot of cooling issues
Yep, totally agree. Thanks bud! 👊
I completely agree. I use a different brand and now see a lower overall engine running temp of 84 degrees Celsius
Hell yea, great real-world feedback! Thanks! 👍
I installed mine yesterday💪🏽
Here's what I don't understand about the cyl 4 cooling mod. So, once installed the hot water from cyl 4 is then connected to a heater core hose. Wouldn't it need to go instead to the radiator to be cooled? Essentially, the hot water is mixed with the hot water in the system. Am I making sense?
@subaruOnly will the killer B oil pan, pick up and baffle kit fit a 2004 Subaru Outback 2.5 Limited
Yes - should fit!! 👍
It might also be because of the header design. With the ports closer, the headers are more compact.
So do you think it’s even worth doing a cylinder 4 cooling mod at all? Since it’s a bad design in a first place?
def worth doing as it helps!
great theroy bud, thank you #subarudoctor gold coast
Straight and to the point makes lots of sense.
You are right
Thanks for the info Luke, it was really good to know.
Cheers buddy! 🍻
Is the intake side the same?
Time 4 bilet heads
Hell yea!!! 🤙
Did the aftermarket billet head/block manufacturers redesign to fix this issue?
great informative video!
Luke love your videos!!!
Would it be possible to get into port 4 with a die grinder and smooth out some of those sharp corners? Give it a bit better flow??
Yes, def. There are some masters out there for sure!!!
@@SubaruONLY You wouldn't by any chance have a video on that would you? LoL
Sorry, don’t. Don’t know of any videos specifically either. Prob find plenty of LS porting videos tho.
@@SubaruONLY No worries, i'll do some searching. Thanks for the replies you earned a sub.
Thanks for the support! 👍
Thx!
Engine mounts in the way
Nice video
Thanks man! 😁
Just had head gaskets replaced on my 2002 legacy outback,2.5,sohc,awd I think the mechanic didn't do such a good job.I think he rushed through it.I told him I wanted multi layer gaskets,not fellpro or graphene and I'm not sure if he did that.Also,I was told he could have put them in backwards.Is there any way to tell without taking the heads off?
Yes, usually there’s a little of the head gasket material sticking out on the sides. Find a spot where you can inspect it and you should be able to see if it’s a MLS (multi layer steel) design - they’re easy to spot as they are just a stack of thin metal vs some solid composite material. Good luck buddy! 👊
So would it be more beneficial for the turbo to be on cylinder 3 i stead? I know someone said the turbo being by 4 could also be causing heat on 4. Just curious.
Might be. Interesting thought. Like it 👍