Thread: 180* T-stat

There is nothing wrong with looking for the balance between performance and efficiency.
The Road and Track take (you can find similar non Internet forum articles everywhere).

Engine-management computers rely on the as-designed coolant temperature (typically 193 degrees F) to better atomize fuel, maintain heat-exchanger efficiency, provide lower emissions, optimize fuel economy and other factors, so running the engine colder than designed can have multiple ill effects. These are the sort of effects that are not immediately apparent, so such issues are more long-term durability concerns.

Tuners often fit 180-degree F thermostats to give hot-rodded engines a larger cooling margin for when they’re making tons of heat (horsepower) at full throttle. This is a bona fide need on an engine that has sprouted a supercharger, but simply fitting a cooler thermostat to a stock engine will not lower the intake air temperature enough to matter and will not support a meaningful timing increase.

Cooler than 180-degree thermostats are not recommended on modern cars. Most domestic automakers’ engine-management systems go into open loop at 168 degrees F, meaning the engine is operating in its warm-up mode with perhaps an overly rich mixture and un-optimized ignition timing. Eventually the computer will consider such long warm-up times abnormal and could trip the Check Engine Light.

Furthermore, higher coolant temperatures promote engine efficiency, especially for fuel economy and emissions, and reduce cylinder wear (a cold block wears faster than a warm block), and the engine internal dimensions have been set for the designed operating temperature. If you’re really beating on your car in the summer and figure it’s overheating, then a 180-degree thermostat could be the answer to return your coolant temps to as-designed levels, but anything colder is counterproductive.


another related thought. If you are running an IC or going to, most rely on the radiator puller fan(s) to cool the FMHE. Typical fans settings with a 180* thermostat is 176 -182* whereas the stock fans settings with the 195* is 208 - 212*.

I'm again going to recommend reading Greg Bannish (GM OEM calibration engineer and performance tuner/teacher) book Engine Management Advanced Tuning, and any other books you can get your hands on.

Originally Posted by TDCRacing

Not true.Not for us anyway. I have never ever seen any .bin file where a car stays in closed loop untill any where NEAR that tempeture.The ECT for closed loop on a stock 2000 GTP is about 50*F, and a stock 98 GTP is about 76.1*F. Even for corvette's ect...The cupple .bin files I have seen for them the Closed Loop ECT is no where near that. I can also promise you that by installing a 160 thermostat will not wash down your cylinders because of excessive fuel or colder block temps.


I would have to agree on the mpg loss. Even though I have not seen any concreate results from myself mostly because I have not been keeping a close eye on it.....

Stock 99 GTP is 68* before allowing open loop. I should have posted where that quote came from. I can't see it in a 3.8 bin but IIRC the knock sensor don't operate until a given temp, which I thought was real close, if not too close the 160* range.

I believe you are very worng on the cyclinder wash running a 160* tstat, and unless you are loaded with money, I wouldn't promise anyone that running a 160 won't cause cyclinder wash. The only place I've seen anyone saying that a 160* on a daily driver car is a good idea is on Internet forums, where people are guessing. In the book I mentioned above, it was stated that most OEM systems are calibrated to 200* for best emissions and combustion. However dropping 20* allows for cooler CCtemps and will let you run a few more degrees of timing thus making more HP. It was also stated that intentially running too cold ETC was reserved for drag racing engines where emmissions and cylinder wash from raw fuel isn't a concern.

Go over to HPTuners ( I know you are a member there, because I've see your questions) and see what the consensus is. fwiw I assume you know Greg is a member there as well.

fwiw, I really don't care whether someone runs a 195 or 180 tstat as it won't harm their engine. I really hate to see some one, who is tight on cash, doing soemthing as from everything I've seen could potential and unknowingly damage their engine.