Go with stock thermostat or a cooler thermostat?

Joel K

Supporter
I am a long way from go cart mode, but figure I’d throw this question out.

I plan to run a Gen V LT4 Engine with a Stock ECU, not a crate ECU due to emissions compliance. Also planning on using the stock ECU to control the brushless fans I picked up. Not sure what temperature they turn on but assume the programming is designed around the 212 degree thermostat. I don’t plan to mod the engine.

The question is, should I consider going with a cooler thermostat. The stock thermostat opens at 212 degrees. Many of the aftermarket companies offer a 160 degree thermostat. If I go in that direction I could modify the ECU program to turn on the fans sooner, or use the SPAL brushless fan switch that came with my kit which ramps the fan speed from min to max as temperature rises from 165 to 175 degrees.

Not sure if the stock engine programming will be happy operating at 160.

Appreciated the feedback.
 

Randy V

Admin
Lifetime Supporter
Joel, an engine will operate with higher efficiency at the higher thermostat temperature- providing you don't run into overheating problems from other cooling system deficiencies.
Exactly..... I’ve sang this song to some of my “old skool” friends until I was blue in the face... Now I just let them think they’re building more HP because of a cooler intake manifold, etc....
 
I probably wouldn't recommend going down to 160, but I think it's worth considering dropping to 185-190 range. This has nothing to do with engine performance and everything to do with engine bay and cockpit temps. The hotter your engine and cooling system runs, the more heat you have surrounding the cockpit. You can insulate until you're blue in the face, but in reality, all the insulation in the world is only slowing down the inevitable. You have the radiator heating up the front, the cooling tubes heating up the sides and the engine heating up the back. The cockpit is literally surrounded by heat....and I would much rather that heat be 195 degrees vs 220. You also have to consider that the engine bay is getting a small fraction of the airflow it would get in a front-engine car....so all of the engine components (fuel injectors, ignition coils, engine sensors, throttle body motor, spark plug wires, etc) are going to be running exponentially hotter than they would otherwise.
 
Unless I’m much mistaken the thermostat only remains closed at initial warm up. Therefore after that and the thermostat is open you’re at ‘system temperature’ which is independent of the thermostat. I’ve gone for a 160deg thermostat on the basis that I wanted a quick warm up period, hence the thermostat, but wanted the main system to take over quickly after that. It seems many GT40s are marginal on system cooling efficiency and mine needs two very high quality 24 Amp Kenlowe fans as fitted to the original cars to keep it cool. They work perfectly.
 

Terry Oxandale

Skinny Man
I think there is another consideration on lower temps, but I'm not sure how it applies to the surface of the cylinder wall (how well is the heat pulled from the wall surface?), but wear decreases significantly with an increase in temperature, up to a point.
 
Unless I’m much mistaken the thermostat only remains closed at initial warm up. Therefore after that and the thermostat is open you’re at ‘system temperature’ which is independent of the thermostat. I’ve gone for a 160deg thermostat on the basis that I wanted a quick warm up period, hence the thermostat, but wanted the main system to take over quickly after that. It seems many GT40s are marginal on system cooling efficiency and mine needs two very high quality 24 Amp Kenlowe fans as fitted to the original cars to keep it cool. They work perfectly.
If you have a sufficient cooling system, the operating temp is going to be just above the t-stat rating. If you install a 160 degree t-stat, your operating temp is going to be around 160-165. A 195 degree t-stat is going to give you an operating temp of around 195-200. If you have a 160 t-stat installed and your engine ends up operating at 200.....that means your cooling system does not have sufficient cooling capacity and eventually you will end up overheating. That is why you needed the high-amp fans....they are simply a crutch to try to compensate for an inadequate cooling system. You are now pulling 50 amps from your alternator, just to run the cooling fans, which is probably taking an extra 10hp just to run the alternator to keep the fans running to keep your engine from overheating.
 
The LT and LS engines were designed to run at higher temps than some people find comfy. Running them significantly lower than their design temp will likely decrease power and economy. I have the stock temp thermostat in my LS7, and am happy with it.

If the concern is with engine compartment temps, there are ways to mitigate that, starting with ducts and fans.

The key point is that temps in the 200-220 range for an LS engine are not "overheating"- they are completely within design temps.
 
Agreed....which is why I would not recommend going down to 160 t-stat. I doubt that would even get you into closed-loop operation...the engine would be constantly running in "warm-up" mode.
 
You are now pulling 50 amps from your alternator, just to run the cooling fans, which is probably taking an extra 10hp just to run the alternator to keep the fans running to keep your engine from overheating.
Great reminder that amperage from the alternator isn't 'free'.
 

Terry Oxandale

Skinny Man
The irony is (for my situation), that higher speeds drive the fans more than the 12v source does, and at the track, has resulted in the blades grenading due to overspeed. For street driving, the fans are needed for long red-lights, or consistent less-than 25 mph driving, which is when the engine is far from max heat output. Ducting for both the fans, and the inlet up to and immediately adjacent to the core are important to ensure you're using the fans/radiator to maximum efficiency.
My setup is probably overkill on the radiator size in that it runs just under the thermostat setting, and has a pronounce but regular hot/warm cycling while driving. That cycling being evident through both the temperature gauge fluctuations, as well as the sudden increase in hot air blowing in my face for about 20 seconds followed by about a minute of normally ambient air (thermostat opens, heats the radiator, then closes and radiator cools off). Only in the dead of summer at 95º plus temps does my system actually fluctuate just above the thermostat setting. On all but those kind of days, I can get away with leaving the fan assembly (both fans and shroud) off the car, even through normally timed red-lights. My core is about 27" x 16" x 3". A great margin but I may reduce it for weight and other reasons in the future.
 
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