Thermostat temps

[whrdnsx]

Just curious, are different temperature thermostats available? OEM or aftermarket?

I'd like to put a slightly lower temp in my NSX maybe an 80 or 85 degree (C) not sure what that is in Farenheit.

 

[Daedalus]

I'd like to put a slightly lower temp in my NSX maybe an 80 or 85 degree (C) not sure what that is in Farenheit.

What's the purpose of running a cooler thermostat? Stock thermostat begins to open at 78*C and is fully open by 90*C.

 

[whrdnsx]

Running a Turbo & thought a slightly lower operating temperature might help avoid detonation. Since the OEM opens at 78 D(c) maybe a 70-80 D(c) might be the go.

 

[Daedalus]

That seems like a fairly inefficient way to address the issue...like using wood to reinforce a steel structure. The cooling system is there to extract energy after combustion, not before. An extra 10* in coolant temp will hardly matter to the mix, as there just isn't enough time or surface area to make a big difference to the intake charge.

The best way to address knock is by lowering intake air temps with an intercooler. Even adding a little duration to the injector pulse has more leverage on safety margin than coolant temps.

 

[Honcho]

These types of thermostats are really intended for circuit racing, where 99% of the time is spent over 6000rpm. All they do is open at a lower temperature, which allows the coolant to reach the radiator earlier in the process. So, when you hit the track, you're using your car's cooling system earlier in the process, which helps prevent the danger of an overheat while the stat is closed. They don't cool your engine any more than a OEM thermostat, so unless you're racing I wouldn't do it.

 

[whrdnsx]

Thanks for the replys, I'm not a newbie. & i know how an engine works. & i know what causes detonation.

I just asked if a lower thermostat is available. Cause I want to maintain a slightly lower operating temperature. I live in a very hot area of Australia.

 

[Honcho]

Low temp stats are available from Mugen and Spoon. Probably a few others too.

 

[Daedalus]

Thanks for the replys, I'm not a newbie. & i know how an engine works. & i know what causes detonation.

I just asked if a lower thermostat is available. Cause I want to maintain a slightly lower operating temperature. I live in a very hot area of Australia.

I'm still unclear on the benefit. If the coolant temp with a stock thermostat is over 90*C, a lower-temp thermostat will not help; in both cases the thermostat is fully open and the coolant is over 90*C. If the coolant temp is below 90* then the car is well within its safe temp range for the engine. If the car's running hot I would suggest a product like Water Wetter might be what you're looking for. It reduces the surface tension of the coolant and enables the cooling system to move more heat into the coolant from the engine and into the radiator from the coolant.

 

[96cxt]

I am running a lower temp theromstat in my NSX. I installed this when I was installing the BBSC kit on my NSX. Everyone that lives here in Houston TX knows it gets really hot in summer so I figured I would run a lower temp thermostat. From my research I bought one from Mishimoto, and it costs about $50 to $60 max.

Acura NSX Racing Thermostat, 1993-2005
The Mishimoto racing thermostat for the Acura NSX will promote greater cooling efficiency throughout your engine. The Mishimoto racing thermostat will significantly lower high engine temperature produced by modified and upgraded turbo applications. Once the engine is fully warmed up the Mishimoto racing thermostat will open up at a lower temperature than standard thermostats, also allowing the coolant to flow through the engine sooner thus reducing and maintaining cooler engine temperatures.

Model: MMTS-S2K-00
MSRP: $60.00

http://www.mishimoto.com/acura-nsx-racing-thermostat-93-99.html

You can also find one from Spoon and Mugen.

After my install along with the BBSC kit, the temp is definely lower on the gauge, but now that it is cold out the car runs cold, the gauge shows significantly lower temp. The bad side to this is that the heater in the car is not hot/warm enough and I'm freezing my tail off. lol So be ready for that.

Good luck and hope this helped you.

Rahim

 

[OLDMNSX]

Don't forget that there are products out there that will lower the coolant temps too. I think that Royal Purple makes a product called "Water Wetter" or the likes there of. I have never used any of these, but know "Street Rodders" that swear by it. Check it out.
Brad

 

[whrdnsx]

Thanks for the info.
Much appreciated.

 

[rsevo6]

With a Turbo, it is certainly a good mod to install a lower temp thermostat.
It will prevent heatsoak of the cooling system when pushing the Turbo as it gives full cooling capacity faster by opening earlier.
With a Turbo the temp rise can be very quick and because of this overheating can occur as it may take a OE thermostat too long to open as it starts from a higher temp.
Lots of Turbokit builders recommend using a lower temp thermostat

 

[Daedalus]

With a Turbo, it is certainly a good mod to install a lower temp thermostat.
It will prevent heatsoak of the cooling system when pushing the Turbo as it gives full cooling capacity faster by opening earlier.
With a Turbo the temp rise can be very quick and because of this overheating can occur as it may take a OE thermostat too long to open as it starts from a higher temp.
Lots of Turbokit builders recommend using a lower temp thermostat

Cooling systems on modern cars are plumbed to ensure the thermostat (and temp sensor!) are kept current with coolant temps at the head. On the NSX there are 3 bypass paths from the rear head to the thermostat chamber, one of which is a short leg solely dedicated to heating the thermostat with coolant directly from the rear head exit passage. Even doubling the stock power output, I strongly doubt you would see a 5*C temp gradient between the thermostat and the head, let alone the 40*C temp gradient that would be needed for the engine to be at risk of overheating with the thermostat closed.

Besides that, "pushing the turbo" should only be done on a car at operating temps, which means the thermostat is already at least partially open. At idle from a cold start, you can put your hand on the coolant hose and feel the rapid heating up of coolant when the thermostat opens.

 

[rsevo6]

Besides that, "pushing the turbo" should only be done on a car at operating temps, which means the thermostat is already at least partially open. At idle from a cold start, you can put your hand on the coolant hose and feel the rapid heating up of coolant when the thermostat opens.

And that is exactly the point of putting in a lowtemp thermostat.
The thermostat is constantly opening and closing dependant on the cooling capacity needed to keep good operating temp, this again dependant on the outside airtemp/radiator cooling ALL the time the engine is running, also when "warm".
The temp addition of a watercooled turbo to the OE cooling system when the turbo is pushed for a short time can be soo great that it may spike way too high before the OE temp reacts, the cooling system "overflows" with too quick temp rise. A lowtemp thermostat opens earlier, thus flattening out the temp spike so it cannot get to a dangerous level

 

[Daedalus]

And that is exactly the point of putting in a lowtemp thermostat.
The thermostat is constantly opening and closing dependant on the cooling capacity needed to keep good operating temp, this again dependant on the outside airtemp/radiator cooling ALL the time the engine is running, also when "warm".
The temp addition of a watercooled turbo to the OE cooling system when the turbo is pushed for a short time can be soo great that it may spike way too high before the OE temp reacts, the cooling system "overflows" with too quick temp rise. A lowtemp thermostat opens earlier, thus flattening out the temp spike so it cannot get to a dangerous level

So now we're talking water cooled turbos. They can be problematic simply because they're adding heat to a system not designed for it. But even these are plumbed off bypass routes that go straight back to the thermostat chamber. The thermostat itself is not an issue. It remains completely open at temps well below overheat. Where, specifically, do you think temperature is a problem? What area gets so hot that it is overheating while the thermostat remains partially closed? How high a termperature are we talking about here?

 

[rsevo6]

I wouldn't expect that any respectable Turbokit builder will use other than a watercooled Turbo, afaik all modern turbo's are watercooled!?

The point is that this when pushed, will add a temp spike to the cooling system and the reaction of a partially closed thermostat will just be too slow so by the time the full cooling capacity is available, the system will be already be in overheating mode. As a low temp thermostat will react earlier, the temp spike will be flattened off faster thus preventing overheating.
Ask me how I know... I have a turboed MX-5/Miata

 

[Daedalus]

Ask me how I know... I have a turboed MX-5/Miata

Well, in *that* case, you MUST be the expert! I have installed/owned a turbo car. Does that make me an expert too? How about the mechanical engineering degree, the A in heat transfer, the straight As in auto tech? How about the project I manage, in which I personally oversee the requirements definition, design and fabrication of many obscenely expensive items, including several dozen that exist solely for the purpose of keeping things at the right temperature under very challenging environments? How about Corky Bell? Is he an expert? I've read one of his books on forced induction cover to cover, and he doesn't mention thermostats at all.

Resumes can be worth the paper they're printed on. How about a technical analysis?
-Assume an impossibly worst case example of an NSX driving with coolant @ 78*C, and thermostat closed
-Driver stomps on the pedal, immediately unleashing 335KW at the crank
-Typical cooling system absorbs 28% of this energy, or 94KW
-Cp of coolant mix is 3.6 KJ/Kg-*C
-Of the 17kg of coolant in the system, about 8kg is trapped by the thermostat on the engine side

At WOT the coolant will rise about 3.3*C per second. Is this what you mean by "spike"? Is it a problem? It will take about 10 seconds before the coolant approaches an overheat" temp (assuming a closed thermostat). If you've ever dropped a thermostat in boiling water, you know it opens in about 3 seconds.

*** The thermostat can react much faster than the coolant temperature can change! This is really all that matters.

As stated, this is an impossibly worst case scenario. The thermostat starts off closed. The problem statement ignores the benefit of the bypass paths. As soon as the coolant rises above 78*C the thermostat will begin to open. The pump, with the engine at 8000 RPMs, moves upwards of 8kg/s of coolant, increasingly through the radiator as the thermostat opens, which will immediatly begin to slow the temp rise of the coolant.

As far as all modern turbos being water cooled, from comments on this site I believe most turbo NSX owners are running oil cooled turbos. I certainly believe most of the kits sold are sold by "respectable" vendors/fabricators.

 

[NSXGeek!]

As far as all modern turbos being water cooled, from comments on this site I believe most turbo NSX owners are running oil cooled turbos. I certainly believe most of the kits sold are sold by "respectable" vendors/fabricators.

No, most are using water cooled turbochargers. While there is thermal transfer between the turbo and the oil around the bearings, the oil's purpose is lubrication. A water jacket turbocharger uses chambers around the bearing to extract heat from the center housing (reducing transfer to the turbo's compressor side). This water jacket shares the engine's coolant circuit in most applications.

 

[NSXGeek!]

What's the purpose of running a cooler thermostat? Stock thermostat begins to open at 78*C and is fully open by 90*C.

The NSX like most road cars will operate well above 172 deg F (78 deg F) - more around 185-190 deg F regulated by the factory thermostat. This is slightly less than optimal for performance, but well suited for reducing emissions. Like most road cars, the stock thermostat uses less radiator capacity than what is available under most conditions (meaning that the radiator can extract more heat than the engine car put in unencumbered by the thermostat). By allowing the thermostat to open fully at a lower temperature, more capacity of the radiator can be used to reduce coolant temperature resulting in lower cylinder temperatures.

This is of course assuming there is radiator overhead capacity which may be reduced by thermal input from ambient temperatures or other inputs like a water jacket turbocharger. Verifying radiator capacity would be easy by monitoring coolant temperature, then changing or eliminating the thermostat. If there is no change in coolant temperature, you need more radiator capacity.

 

[whrdnsx]

I knew this would open a can of worms!

Here's one for you. why do 99% of purpose built race engines (not OEM based) do not use Thermostats?

 

[Daedalus]

The NSX like most road cars will operate well above 172 deg F (78 deg F) - more around 185-190 deg F regulated by the factory thermostat. This is slightly less than optimal for performance, but well suited for reducing emissions. Like most road cars, the stock thermostat uses less radiator capacity than what is available under most conditions (meaning that the radiator can extract more heat than the engine car put in unencumbered by the thermostat). By allowing the thermostat to open fully at a lower temperature, more capacity of the radiator can be used to reduce coolant temperature resulting in lower cylinder temperatures.

If you're adding a turbo to a car, and presumably trying to enhance performance, why would you want lower cylinder temperatures? You're not going to pass an emissions test while driving the car hard, with or without a turbo. And if you're driving the car hard, the stock thermostat is fully open.

I knew this would open a can of worms!

Here's one for you. why do 99% of purpose built race engines (not OEM based) do not use Thermostats?

Probably because they're not concerned about emissions or the time it takes for the engine to warm up. Purpose built race engines have purpose built cooling systems. Why do you use a thermostat?

 

[rsevo6]

@ Daedalus:
I know and am expert because I have personal real world experience with the result of changing thermostats to a lower temp version on both supercharged and turbo kitted Miata's.

From your manner of writing it is clear that you on the other hand are theoretically 100 % certain of your own opinion that this useless.

So please stay with your opinion, I have no intention of entering into a pointless discussion with someone who is clearly unbendable in his opinion and when someone else (like me) differs from that opinion and has REAL world experience telling different, you start writing in a sarcastic tone attempting to put the other person down.
Your reaction on the input of NSXgeek confirms this.

Whell on me this doesn't work in any way.
End of discussion afaic, will not be reacting on this any further, is clearly useless.

 

[rsevo6]

Last addition:
I wonder why so many tuning parts suppliers and tuning companies are offering lower temp thermostats as according to YOUR opinion they are completely useless anyway

 

[Daedalus]

Last addition:
I wonder why so many tuning parts suppliers and tuning companies are offering lower temp thermostats as according to YOUR opinion they are completely useless anyway

Well, at $60 each they're extremely profitable...as are fuel line magnets, electronic rust protectors, and the Vornado.

What I can't figure out is how someone can have so many posts in this thread yet not be able to relate anything particularly useful from their personal real world experience. Surely this personal real world experience contains hard data, from which objective decisions can be made.

My personal real world experience involves wrenching on cars for over 15 years. It involves a 4-car garage full of tools and instruments. It involves a LOT of measurements. As I said, I know how long it takes for a thermostat to open. I've measured the decibel levels my car makes at every 1000 RPMs inside the cabin, with and without headers. I've measured the temperature profile of my cats at idle from a cold start. I've measured my coolant temperature at idle and after a spirited drive (after verifying the calibration of the temp sensor). I've measured my oil pressure throughout the powerband. I've measured my fuel pressure. I know how long it takes before my O2 sensors start to kick in. I know how many kV my coils generate. I know my cylinder compression. I've measured the size of each of my cam lobes. I know the temperature of my rotors after a single panic stop. On another car I know how much vacuum it takes to work the EGR valve. On that car as well I know how many amps a new fuel pump requires vs. one that has 120k on it. I measure the runout of all my rotors after every brake pad change. I even know how many watts most electrical things in my house consume. And believe me, I'll be spending many hours at work this year and next for qual testing things after they're built. Did you honestly go through this type of rigor in understanding cause and effects when changing thermostats?

I'm more than theoretical, but theory is very important. If we only relied on experience imagine how many bridges and skyscrapers would collapse each year. If you want to disagree with theory, be prepared to back it up with useful info. Vendor marketing BS doesn't count.

 

[96cxt]

Well, in *that* case, you MUST be the expert! I have installed/owned a turbo car. Does that make me an expert too? How about the mechanical engineering degree, the A in heat transfer, the straight As in auto tech? How about the project I manage, in which I personally oversee the requirements definition, design and fabrication of many obscenely expensive items, including several dozen that exist solely for the purpose of keeping things at the right temperature under very challenging environments? How about Corky Bell? Is he an expert? I've read one of his books on forced induction cover to cover, and he doesn't mention thermostats at all.

Resumes can be worth the paper they're printed on. How about a technical analysis?
-Assume an impossibly worst case example of an NSX driving with coolant @ 78*C, and thermostat closed
-Driver stomps on the pedal, immediately unleashing 335KW at the crank
-Typical cooling system absorbs 28% of this energy, or 94KW
-Cp of coolant mix is 3.6 KJ/Kg-*C
-Of the 17kg of coolant in the system, about 8kg is trapped by the thermostat on the engine side

At WOT the coolant will rise about 3.3*C per second. Is this what you mean by "spike"? Is it a problem? It will take about 10 seconds before the coolant approaches an overheat" temp (assuming a closed thermostat). If you've ever dropped a thermostat in boiling water, you know it opens in about 3 seconds.

*** The thermostat can react much faster than the coolant temperature can change! This is really all that matters.

As stated, this is an impossibly worst case scenario. The thermostat starts off closed. The problem statement ignores the benefit of the bypass paths. As soon as the coolant rises above 78*C the thermostat will begin to open. The pump, with the engine at 8000 RPMs, moves upwards of 8kg/s of coolant, increasingly through the radiator as the thermostat opens, which will immediatly begin to slow the temp rise of the coolant.

As far as all modern turbos being water cooled, from comments on this site I believe most turbo NSX owners are running oil cooled turbos. I certainly believe most of the kits sold are sold by "respectable" vendors/fabricators.

I like the way you think. I would like to ask you a few question please:smile:
Ok so an NSX was built as an all motor car and the cooling system was made for the NA motor. Now we are adding a turbo charger to the mix.

As you already know:

1)The turbo runs off the exhaust gases of an engine creating back pressure between the heads and the turbo to push the wheel on the turbo, now the back pressure in the headers have more energy causing more heat then stock, therefor the heads of the car are at a higher temp now.

2) Since the turbo runs from the exhaust gasses the turbo spools up causing it to reach very high temps (i think over 1500 degrees), being it a watercooled turbo the coolant temps are pretty high now.

You stated that the coolant temp will increase at 3.3*c at WOT is this the same for NA motors and FI motor? Then is it same for FI motors at low boost as to high boost as to extreme high boost? I would like to know this because I have a turbocharged honda civic 2.0 GSR motor and I can go from making 300 whp to 800whp with a flip of a switch on the boost controller. It makes 800whp at about 32-34 psi of boost on a fairly large turbo so does the equation stay the same? The more air and fuel I pack in the cyclinder the the more power I make creating more energy that needs to be absorbed by the coolant.

I'm quoting this directly from Garrett http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html

Oil & Water Plumbing

The intake and exhaust plumbing often receives the focus leaving the oil and water plumbing neglected.

Garrett ball bearing turbochargers require less oil than journal bearing turbos. Therefore an oil inlet restrictor is recommended if you have oil pressure over about 60 psig. The oil outlet should be plumbed to the oil pan above the oil level (for wet sump systems). Since the oil drain is gravity fed, it is important that the oil outlet points downward, and that the drain tube does not become horizontal or go “uphill” at any point.

Following a hot shutdown of a turbocharger, heat soak begins. This means that the heat in the head, exhaust manifold, and turbine housing finds it way to the turbo’s center housing, raising its temperature. These extreme temperatures in the center housing can result in oil coking.

To minimize the effects of heat soak-back, water-cooled center housings were introduced. These use coolant from the engine to act as a heat sink after engine shutdown, preventing the oil from coking. The water lines utilize a thermal siphon effect to reduce the peak heat soak-back temperature after engine shut down . The layout of the pipes should minimize peaks and troughs with the (cool) water inlet on the low side. To help this along, it is advantageous to tilt the turbocharger about 25° about the axis of shaft rotation.

Many Garrett turbos are water-cooled for enhanced durability

You stated above about using oil cooled turbos, the oil going to the turbo is not for cooling purposes, but the oil supply is for the bearing in the center of the turbo.

Now lets just take into account all the extra heat/energy we have added to the mix of a stock cooling system. So accordingly the cooling system need to be brought up to par, which would mean upgrading to a larger/more coolant capacity radiator and what ever else it takes to keep everything under good operating condition.

I agree that just changing the thermo to a lower *thermo is not enough but I think it gives many a peace of mind, also does having a lower temp thermo hurt the engine in any way? if not then its phycological insurance for the driver or builder and is worth the $50 or $60 to them.

P.S. I don't have a degree in anything yet but have alot of hands on experience (not intended towards anyone):tongue:

Thanks
Rahim