Reducing Underhood Temperatures 101: M45, M35

[M4point5]

I wanted to start a thread dedicated to reducing underhood temps for the M series - more specifically the M45. Anyone who owns one knows that it is like an oven under the hood after driving for any decent amount of time - "heatsoaked" we can say. I can't speak firsthand about the M35 getting as hot under the hood, but any info here can most definitely be beneficial.

First thing's first - heat robs power. Period. You may notice when it is colder outside, your car will feel like it has more power than if it is hot out. Generally, for every 10 degree temperature drop, you free up 1% horsepower. It doesn't sound like much, but let's throw an example out there. Say your car is making 250hp to the wheels at an underhood temp of 180* (who knows if it gets that high but this is theoretical). If you are able to reduce temps by 30* (at the intake manifold), you have just now freed up 3% more power which equates to 7.5hp. So just by reducing your IAT by 30*, you gained 7.5hp. Not bad right?

Aside from the exhaust manifolds, the radiator, radiator hoses, etc. all radiate a good amount of heat. Heat is transferred from the head to plenum and throttle body, thus robbing you of power EVEN IF you have a cold air intake sucking in 70* air from outside. The cold air you are taking in will be much hotter once it hits your combustion chamber - it doesn't matter WHAT car you have. We know this already. So in order to reduce these IAT's, reducing the amount of heat that is radiated will help tremendously.

Thermal wrap or tape on the radiator hoses, radiator heat shield, fuel line insulating (wrap or tape), plenum spacers, throttle body spacers and exhaust manifold wrapping will reduce the amount of heat radiated and held in the engine bay. With the way the M engine bay is set up (specifically the 45), the upper radiator hoses run pretty close to the throttle body. Any heat radiated from the hoses will essentially be trapped under the engine cover and of course cause heatsoak on the throttle body. Being aluminum, that heat transfers to the lower plenum and ultimately the upper plenum.

We want to eliminate as much radiated heat as possible here. I will be providing real-world tests and record them in this thread. I will be using an infrared thermometer to note the temperatures of the radiator hoses, throttle body, upper plenum, lower plenum, exhaust manifolds, etc.

In addition to that, I will then be wrapping all components, adding throttle body and plenum spacers (these are currently NOT mass produced aftermarket, but I am having some made at a local shop) and also getting the upper plenum thermal coated. After this, I will be performing the same driving tests and conditions and recording the temperature results. I know underhood temperatures will be reduced - my MAIN point of wanting to do these tests is to see if the plenum spacers will REALLY reduce temperatures as they are supposed to.

Additionally, I will be getting retuned after these "mods" are done. I have the dyno graph from when my car was initially tuned, so any improvement on those numbers will be the direct result of plenum and throttle body spacers and heat reduction. Further tuning may improve power output as well - we will see.

Feel free to discuss.

[M4point5]

As promised, here are the "before" temperatures. Vehicle was driven for 20 minutes in the city, turned off for 5 minutes then driven back home 20 minutes, taking the highway. The last ~10 minutes were back to city driving. Car was shut off and temps recorded after approximately 3 minutes (had to find the infrared thermometer).


Throttle Body Elbow



Right Radiator Hose



Intake Pipe



Left Radiator Hose



Throttle Body



Front Of Plenum



Rear Of Plenum

[M4point5]

Updated 06/20/13:
Results after Throttle Body Coolant Bypass AND Intake Plenum Performance Thermal Coating

Vehicle was driven for 15 minutes, idled for 5 minutes, turned off for 15 minutes (Sea Foam treatment) then driven for 15 minutes. Speeds of up to 60mph were achieved. Car was then turned off and temperatures were immediately recorded.

Throttle Body Elbow - 28* Cooler
Right Radiator Hose - Remains Same
Intake Pipe - 24* Cooler
Left Radiator Hose - 1* Warmer
Throttle Body - 26* Cooler
Front of Plenum - 42.5* Cooler
Rear of Plenum - 30.5* Cooler

I am pretty sure that the coolant bypass alone is responsible for the elbow, throttle body and intake pipe temperature reduction. There is no 180* coolant flowing through the elbow anymore, thus resulting in lower temps. The thermal coating on the plenum reduced temps a whopping 42* up front and 30* in the rear!!


Throttle Body Elbow



Right Radiator Hose



Intake Pipe



Left Radiator Hose



Throttle Body



Front of Plenum



Rear of Plenum

[svard75]

Sounds like a good plan. I used the thermal wrap on headers on my past projects and it made a significant difference. The only issue was because the thermal wrap was prone to trapping moisture my headers corroded and rusted quicker. Your pipes won't rust so that's a great start and I believe our headers already have heat shields ( unconfirmed ).

If you live in a warmer climate place you can perform the tb coolant bypass mod. For the m35 VQ35 engines the thermal lower plenum gasket helps a bit and the upper spacer. I Removed all of the engine covers and am leaving them off. That plastic keeps plenty of heat in the engine bay. Any air intake system will get hot as well so try and wrap that up with the thermal wrap. One more thing that makes a big difference is replacing your thermostat with a lower temp rated unit. This essentially forces the coolant to circulated more frequently at lower temps. The drawback is if you are in colder Climates it takes longer for the cabin to heat up.

[Ilya]

In addition to that, I will then be wrapping all components, adding throttle body and plenum spacers (these are currently NOT mass produced aftermarket, but I am having some made at a local shop)

They are mass produced. Motordyne and a couple of other places sell them. I have the Motordyne 5/16" Copper Iso Thermal Spacers.

Good thread though, good luck.

[mexillis]

Good stuff. How much of an advantage is it to lower the thermostats? I know someone previously did that and found out we have two thermostats. I have added the tb bypass and have had zero issues in winter environments. I also put in the additive from royal purple to lower the temp of the radiator. I know everyone says colder air coming in from a cai is good but all the data I've seen is it doesn't work for our car (45). Some lost power when adding the injen and I don't understand that. As for heat soak I don't think we have it that bad, when I go to the track after a few runs I run consistent times back to back. (Maybe I don't fully understand heat soak???)

[svard75]

http://www.rhdjapan.com/nismo-low-temp- ... 35de-55791 Very nice! Very expensive for a thermostat!!!

mexillis a thermostat will open up much sooner allowing the coolant for flow from the rad to the engine and back reducing the engine temps. According to the link I posted it reduces the engine temps from 76 to 68C.

Here is a great article which explains our cooling systems. http://vq35.com/2010/07/go-with-the-flo ... ng-system/

I believe you are right in that the VH45 has two thermostats. But I think you guys are more in luck because it appears they are standard looking. The stupid VQ35 thermostat is part of the housing. According to the cooling system article regardless of the thermostat temps the rear of the VQ35 engine does not get proper cooling regardless. Sux for us.

[Double E]

+1 on the TB coolant bypass mod. It's easy to do and gives an opportunity to clean out the TB if you want...just don't move the butterfly valve AT ALL and disconnect the battery before removing it.

[M4point5]

In addition to that, I will then be wrapping all components, adding throttle body and plenum spacers (these are currently NOT mass produced aftermarket, but I am having some made at a local shop)

They are mass produced. Motordyne and a couple of other places sell them. I have the Motordyne 5/16" Copper Iso Thermal Spacers.

Good thread though, good luck.

Right - mass produced for the VQ35, not VK45 as I was talking about

[M4point5]

+1 on the TB coolant bypass mod. It's easy to do and gives an opportunity to clean out the TB if you want...just don't move the butterfly valve AT ALL and disconnect the battery before removing it.

When I put my intake on, I cleaned the throttle body and opened it up manually. Nothing happened?

[Ilya]

Right - mass produced for the VQ35, not VK45 as I was talking about

Fail on my part. Early morning reading fail to be exact

[M4point5]

Its all good brother, soon there will be a spacer for the VK. I actually contacted several different companies and none were willing to do it based on the fact that there isnt enough interest. The one company I did find didnt know pricing. So I am taking the liberty to have them made myself. If any real world results and gains are found, it will surely be updated in this thread (and even if results are negative)

[M4point5]

Updated POST #2 with "before" results.

[DeanM45]

It would help if you list the ambient temperature as well. Another good temp point is the side of the strut tower (next to the exhaust manifold). Also, if you have a scanner, record what the IAT (intake air temp) is. When cruising, the car runs "lean" so the exhaust manifolds heat up a good deal more (this is information more for the driver's side where the heat can propagate to the intake piping/tb).

[M4point5]

68* out at the time. Dont have a scanner and the plenum is off now so no more driving until its put back together.

Also, factory tune runs lean...I was Osiris tuned so I dont think it will be the same. I will get the strut tower when everything is back together.

[svard75]

M4point5 - what grade gas did you use when getting tuned vs what you use now? I used 91 and found when I filled up with 94 the car stopped knocking. I guess I was running lean?

[M4point5]

M4point5 - what grade gas did you use when getting tuned vs what you use now? I used 91 and found when I filled up with 94 the car stopped knocking. I guess I was running lean?

Factory settings run lean - it isnt really good to run too lean for too long. You run leaner, you make more power...dangerous power. They probably did that to achieve the hit certain numbers (which are crap to me). I am on 92, tuned on 92. But I hate my tune due to the experience. After the plenum gasket, etc. I will be retuned by another shop.

[bejjutsu]

Great thread! (bookmarked)

[Double E]

+1 on the TB coolant bypass mod. It's easy to do and gives an opportunity to clean out the TB if you want...just don't move the butterfly valve AT ALL and disconnect the battery before removing it.

When I put my intake on, I cleaned the throttle body and opened it up manually. Nothing happened?

Hmmm, battery was connected? Did you disconnect the TB wiring as well? I sucessfully cleaned mine and didn't move the B valve and it was fine. Did it again on another M45 (same year), moved the valve slightly and it required a re-learn procedure.

Maybe I never disconnected it completely the first time?

[M4point5]

Battery was connected and I left the tb wiring connected. I opened it all the way up and cleaned.

But NOW I took it off since I took my plenum off and I am going to do the entire relearn procedure after everything is back together. The 45 has the same relearn procedure as the 35, correct?

[Larz]

I find this thread to be quite interestng and I'm learning by reading it. I have a question though. If you wrap rad hoses, couldn't that harm the hose itself by preventing it from being able to shed its own heat? Wouldn't that cause the hose to dry out and become brittle?
The reason I never upgraded the intaken pipe is that I reckon the heat in the engine bay will undo any reduction in air temp by the time it reaches the TB, so why can't we just wrap the intake pipe to preserve the cooler air going through it?
OK that was 2 questions and forgive me if I seem daft for asking, but seriously it seems to make sense to a non-mechanic like myself.

[M4point5]

That is one thing I was contemplating - whether or not the hose itself would be affected by doing it that way. One thing would be to use silicone radiator hoses THEN wrap them. Problem solved. Unfortunately, there are no silicone radiator hoses for the M

[svard75]

Hey guys. In support of this I bought the nismo 62 degree thermostat for the vq35. Ill do a small test once it arrives. I am afraid that this could cause my emissions to fail. Hope not lol

[M4point5]

Lets specify Celcius...whoch is 142* Fahrenheit. Quite a bit lower than stock, but do remember that the engine is built around running most efficiently at 180-190* which is why the thermostats are made as such. Lowering the coolant temperatures will cause efficiency issues. Cuttinf down radiated heat and cutting down coolant temperatures are two different things, but I am interested for your results.

[svard75]

Well this sums it up well. Lowering engine temps will not necessarily increase performance as long as its within normal operating a temps. Read this very comprehensive article.

http://www.tuneruniversity.com/blog/201 ... advantage/

[DeanM45]

Correct, lowering engine operating temperature (coolant) will not necessarily increase power unless the engine is running too hot producing pre-ignition (detonation), fuel vaporization in the lines, and/or raising the intake air temp. Lowering the engine operating temperature can and often does increase friction (higher viscosity for the fluids --thicker, also because of different expansion rates of the various materials in the motor - more mechanical friction). The key to more power is to get the intake air and the fuel to the coolest possible level. The most power on on a dyno is usually achieved with an operating temperature around 190 F, lowest combined emissions around 200F and greatest efficiency (mileage) at 195. All of this is geared around computer controlled, normally aspirated, fuel injected cars.

[M4point5]

Post #3 has been updated with "after" results. This is NOT including plenum and throttle body spacers, as I have yet to have these made. Results are pretty impressive so far.

[pedsemdoc]

Updated 06/20/13:
Results after Throttle Body Coolant Bypass AND Intake Plenum Performance Thermal Coating

what performance thermal coating did you use, if I might ask?

about to install my R2C intake and have thermal wrap for my intake tube (Dean's already done that) and some heat barrier i'm gonna put on the air box facing the plenum, so looking to really minimize temps under the hood.

thanks for all this research you've been doing.

Craig

[M4point5]

There is a local shop I use that specializes in thermal coatings for exhausts and such. The coating itself is Chromex....I know there are places online that sell it BUT I am not sure if you could apply it yourself, as it needs to be baked in the oven several times to cure, in excess of 500*.

[EniGmA1987]

That is one thing I was contemplating - whether or not the hose itself would be affected by doing it that way. One thing would be to use silicone radiator hoses THEN wrap them. Problem solved. Unfortunately, there are no silicone radiator hoses for the M

Why cant you just buy a 25' roll (or whatever) of silicon tubing in the size you need and then do it all yourself?
http://www.usplastic.com/catalog/item.a ... &catid=799