Thread: Thermostat Curiosity

Stock GM 195 thermostat: is 195 the "full open" temperature or the "start to open" temperature? Reason I ask is my operating temp when at speed. I know the fans dont kick until well over 200, but when im cruising the temp (according to my OBD reader) goes up to 190 then starts to fall back, sometimes as low as 181 if its cold out and the heat is on full blast. On the highway, heat on or off, it stays between 186 and 190.

Im just wondering if the previous owner didnt slap a 180 in there, because i thought that the rated temperature was the point it started to open. If that be the case, it would make sense that by 190 its open enough to circulate coolant efficiently.

I believe it is the start to open temp

thought so too. I know Stant thermostats are like that, but wasnt sure about OE. I wonder if there is a reason the previous owner put a 180 in there or if i should switch it back to a 195. Perhaps he got weirded out by the gauge going past the center line when idle(fans come on at 220ish)? If a 195 is fully open at 210, then its plausible that on a hot day and under load, it might run closer to 220 (first line after the big middle mark)

typical GP for ya, they get hot while sitting

I'm positive that 195 is the temperature at which the thermostat begins to open. I wondered myself, so I once stuck a thermostat in a pot on the stove and watched the thermostat alongside a thermometer. Science geek here. lol

Just run a 180*

180* is not needed. Run stock 195*.

You can run a 180 no problem. A tune to turn the fans on earlier will help too.

No car should ever hit 220 while just driving around. Sitting in traffic on a super hot day I'm sure it could happen.

The 195 thermo in my car works like it should, car will sneek up to about 203-204 before the T-stat becomes fully open then drops back to 195-198 all the time and stays there.

Fans are 212 and 226 IIRC.

For the OP, just leave it as is, its been wokring fine for you from what I see.

195 vs 180 degree thermostats in our cars are still a subject of debate. Yes, you can run either temperature with no problems. Typically, a hotter thermostat will reduce engine wear, give you better fuel economy, reduce emissions (perhaps keep your catalytic converter healthier), and give you better heat. A colder thermostat can possibly reduce knock by a small amount, and give you a slightly larger safety cushion as far as overheating goes.

It's only a slight safety cushion because at 215*, both are completely open and protect your engine the same amount, provided they are working correctly. A 180 will simply open up first, but like fivefingerdeathpunch said, the fans don't even turn on until over 200 anyway. It will just take slightly longer to get overheated because the coolant is circulating sooner.

Either way, I think people lose sight of the true job of a thermostat. It's job isn't to cool off your engine... it is to control your engine's temperature. If "as cool as possible" was the only important factor, there would be no point to having a thermostat at all.

Every grand prix I had ran a 160* would rurun at 170 and change. But that was Florida in mid summer with dead cooling fans while rolling

Here we go LOL....

thank you all for your replies. I did not mean for this to be a big debate over 180 vs 195. There was plenty of that going on before I got here. I do like dsmuts idea of tuning the car to have the fans come on sooner, but im too cheap to get a tuning kit. Im assuming it is a 180 based on what y'all have said. I believe the car should run a little warmer esp during the winter, but stock settings are overkill, every other car i have driven runs between 180 and 200, maybe 210 under load when its 100 degrees out. I am considering switching it back to a 195. From all ive read, the gas mileage is better when the car is hotter and the 3.8s like being on the warm side.

Im posting up the pic from my other thread, the one about hitting 222,222 miles. I had been on the road for about 20 minutes with the heat on. Notice the temp gauge, that reading is appx 175 degrees. At 32 degrees outside, the gauge should not be falling that far. Since the weather started cooling off, and ive had a good water pump and elbows, my gas mileage has fallen to 21.5 average. It had been ~24 all summer. With a dodgy water pump and leaking elbows, it was running 200-215 all the time.

I run a 180* with fans tuned for it in Chicago. It gets cold here sometimes. No issues.

Your stock gauge isn't accurate. You can't really go by it for precise measurement.

these cars are designed to be cooled by the air while driving really well, my car has a stock t stat in it and never hits operating temperature unless im driving ovver 30miles typically. ive gone weeks without the t stat ever opening up and me driving it every day

Then your thermostat is stuck open or you don't drive far enough for it to open. My thermostat is open by the time i'm 2 miles down the road.

I am at full operating temp within 3-5 miles. Definitely sounds like a stuck open thermostat.