How the VQ35DE cooling system works - reverse engineered by taking apart an engine I have on a stand: The two hose barbs bolted to the side of the block, behind the thermostat, are the bypass hose (the one you are removing) attached to the front barb, and the hard line combining the coolant return from the heater core and the return from the throttle body warmer, both going to the rear barb. I pulled the thermostat to look at the internal routing. The front barb (the bypass you removed) is routed internally to flow directly over the thermostat - obviously using hot coolant from the cylinder heads to control thermostat opening. The oil cooler hose, while it enters the front of the housing, flows parallel to the thermostat, not directly over - perhaps it's "in the mix" but the oil may heat it hotter than the average coolant temperature and thus they don't want it opening the thermostat prematurely. The oil cooler bypasses the radiator so that the oil temperature is regulated even when the thermostat is closed. The combined throttle body coolant return / heater core return are actually *shielded* from the back of the thermostat - likely the heater core cools the coolant enough that it would result in the thermostat remaining closed until the block gets too hot. Remember, this isn't just about emissions but also thermal expansion and mechanical tolerances like bearings and piston-to-cylinder, which incidentally might increase emissions if it gets too hot. Now, there are track cars which run without this front bypass hose, without the OEM oil cooler, without a heater core, bypass the throttle body, and "seem to be" OK... That's not the same as going 200k miles without replacing otherwise low maintenance items like the water pump or crank bearings or piston rings... I have heard you absolutely must keep a bypass line from the back pipe to an inlet on the water pump side if you delete this hose *and* the throttle body heat and/or heater core - if you delete all 3 and have no bypass back to the thermostat, most likely your thermostat will not open before the block is overheating, the coolant is boiling over, and you are killing your pump from cavitation. According to the factory service manual, the only way coolant enters the pump is through the back side of the thermostat cavity, and those 3 barbs are the only circulation when the thermostat is closed. TBD: I have not (yet) removed my heater core to know if it has any valves to stop flow through it - a thermostat for the heater core would speed warmup for emissions but I don't see one on the engine side of the firewall and it wouldn't be consumer friendly to deny you air even a couple degrees warmer when it's cold outside (but I could see them doing it for emissions). I also can't find a mention of a heater core valve / thermostat online or in the factory service manual, so unless there's one as a non-replaceable part of the OEM assembly, there's not one. Everything I can see from the outside of the heater core unit suggests they control air flow through the core to turn off the cabin heat. On the other hand, I've heard you need to turn the heat up when you are bleeding the coolant, which wouldn't make much difference if there's no valve for the coolant - so one of these things is wrong...
@@latenightgarage7895 Why? Running your engine cooler will mean tighter clearances, shorter bearing life, more friction, less power, etc. The thermostat changes the operating temperature - it doesn't increase maximum cooling. You want a bigger radiator if you want more maximum cooling. If overheating is a problem and you aren't using forced induction, you have a different problem (probably a coolant leak, not allowing pressure to build, air in the system, or improperly modified coolant routing).
@justtheotherdave took the words right off my fingertips. Nissan engineers spent alot of $ to configure this engine. Which has been used for decades, in many different Nissan and Infiniti automobiles. Kinda like the air intake, and straight piping the car. If you don't know what you are doing, you will lower the horsepower, and even worse, damage components. There are vids out there of stock G35 on dyno, then same G35 is straight piped, with a pop charger and the car lost 14 horse. But 😂 sounds good 🤮
Na, but you can find the parts at autozone for a few bucks, I think I show the number and what there called in the video. Just remember to buy some clamps.
I'm sure it's for cars that are running during the winter, it's a bypass for the thermostat so that the engine will warm up quicker. If your like me and don't drive during winter it's not a problem, plus you can buy a thermostat that opens at a lower temp to circulate coolant through the motor sooner.
All it does is bypass warm coolant past the thermostat to warm the car up during cold temps. I drive during the summer so I don't worry about it. I plan on adding a low temp thermostat, it opens at a low temp helping the motor say cooler.
@@justinrb2918 From what I read up on is that this hose is ment for warming up the oil, for example like on a cold morning. So if you drive your car in cold conditions I would put it back on, and then take it back off during summer, same can be done with the coolant lines running through your upper plenum by the TB.
If you live somewhere north of Florida I don't recommend this, the oil cooler runs to the front of the thermostat but it can't keep up with the flow of coolant and without this bypass hose at colder times the rad cools faster then the motor and the thermostat doesn't open and you over heat. Side note you're super lucky you didn't get air trapped in your system it's a nightmare to bleed this sucker.
How the VQ35DE cooling system works - reverse engineered by taking apart an engine I have on a stand: The two hose barbs bolted to the side of the block, behind the thermostat, are the bypass hose (the one you are removing) attached to the front barb, and the hard line combining the coolant return from the heater core and the return from the throttle body warmer, both going to the rear barb. I pulled the thermostat to look at the internal routing. The front barb (the bypass you removed) is routed internally to flow directly over the thermostat - obviously using hot coolant from the cylinder heads to control thermostat opening. The oil cooler hose, while it enters the front of the housing, flows parallel to the thermostat, not directly over - perhaps it's "in the mix" but the oil may heat it hotter than the average coolant temperature and thus they don't want it opening the thermostat prematurely. The oil cooler bypasses the radiator so that the oil temperature is regulated even when the thermostat is closed. The combined throttle body coolant return / heater core return are actually *shielded* from the back of the thermostat - likely the heater core cools the coolant enough that it would result in the thermostat remaining closed until the block gets too hot. Remember, this isn't just about emissions but also thermal expansion and mechanical tolerances like bearings and piston-to-cylinder, which incidentally might increase emissions if it gets too hot.
Now, there are track cars which run without this front bypass hose, without the OEM oil cooler, without a heater core, bypass the throttle body, and "seem to be" OK... That's not the same as going 200k miles without replacing otherwise low maintenance items like the water pump or crank bearings or piston rings... I have heard you absolutely must keep a bypass line from the back pipe to an inlet on the water pump side if you delete this hose *and* the throttle body heat and/or heater core - if you delete all 3 and have no bypass back to the thermostat, most likely your thermostat will not open before the block is overheating, the coolant is boiling over, and you are killing your pump from cavitation. According to the factory service manual, the only way coolant enters the pump is through the back side of the thermostat cavity, and those 3 barbs are the only circulation when the thermostat is closed.
TBD: I have not (yet) removed my heater core to know if it has any valves to stop flow through it - a thermostat for the heater core would speed warmup for emissions but I don't see one on the engine side of the firewall and it wouldn't be consumer friendly to deny you air even a couple degrees warmer when it's cold outside (but I could see them doing it for emissions). I also can't find a mention of a heater core valve / thermostat online or in the factory service manual, so unless there's one as a non-replaceable part of the OEM assembly, there's not one. Everything I can see from the outside of the heater core unit suggests they control air flow through the core to turn off the cabin heat. On the other hand, I've heard you need to turn the heat up when you are bleeding the coolant, which wouldn't make much difference if there's no valve for the coolant - so one of these things is wrong...
You could get a low temp thermostat to help it open faster.
@@latenightgarage7895 Why? Running your engine cooler will mean tighter clearances, shorter bearing life, more friction, less power, etc. The thermostat changes the operating temperature - it doesn't increase maximum cooling. You want a bigger radiator if you want more maximum cooling. If overheating is a problem and you aren't using forced induction, you have a different problem (probably a coolant leak, not allowing pressure to build, air in the system, or improperly modified coolant routing).
@justtheotherdave took the words right off my fingertips. Nissan engineers spent alot of $ to configure this engine. Which has been used for decades, in many different Nissan and Infiniti automobiles. Kinda like the air intake, and straight piping the car. If you don't know what you are doing, you will lower the horsepower, and even worse, damage components. There are vids out there of stock G35 on dyno, then same G35 is straight piped, with a pop charger and the car lost 14 horse. But 😂 sounds good 🤮
@@speedracer2831 Nissan removed the hose that's in this video on the newer engines.
@@TurboV8boi removed, or moved? There is a specific reason for that hose.
Are the caps 3/4s or 5/8s
3/4s part# 02251
Any links to the parts on Amazon or eBay ?
Na, but you can find the parts at autozone for a few bucks, I think I show the number and what there called in the video. Just remember to buy some clamps.
There's a reason why engineers meet the coolant system for that the way it is.........😮
Why
Over engineered motor
I'm sure it's for cars that are running during the winter, it's a bypass for the thermostat so that the engine will warm up quicker. If your like me and don't drive during winter it's not a problem, plus you can buy a thermostat that opens at a lower temp to circulate coolant through the motor sooner.
@@latenightgarage7895 Yeah ik , mostly for colder climates too. I live in florida So doesn’t get that cold for me anyway
how is the car still running? i want to do this mod but im worried
All it does is bypass warm coolant past the thermostat to warm the car up during cold temps. I drive during the summer so I don't worry about it. I plan on adding a low temp thermostat, it opens at a low temp helping the motor say cooler.
@@latenightgarage7895 thankyou for the reply!! Really appreciate it!! Everyone else not so helpful
How is the car doing so far ?
It's still good
@@latenightgarage7895 what state are you in ??
Why?
@@latenightgarage7895 just curious if you are in a hot or cold climate
Oh I'm in CO, last weekend it was cold out and the heater worked fine, the temp on the dash is where it's always been at
did you tune it after you got the kinetix plenum ?
No, doesn't really need a tune to add performance
Still running good ?
Yeah
Cool I'm going to do mine
@@justinrb2918 From what I read up on is that this hose is ment for warming up the oil, for example like on a cold morning. So if you drive your car in cold conditions I would put it back on, and then take it back off during summer, same can be done with the coolant lines running through your upper plenum by the TB.
If you live somewhere north of Florida I don't recommend this, the oil cooler runs to the front of the thermostat but it can't keep up with the flow of coolant and without this bypass hose at colder times the rad cools faster then the motor and the thermostat doesn't open and you over heat. Side note you're super lucky you didn't get air trapped in your system it's a nightmare to bleed this sucker.