I've noticed that a lot of Bonneville owners list a 180 degree thermostat as a performance mod on their cars and it has left me wondering. Maybe with a */C engine you want to go with a lower temp thermostat, but on normally aspirated I wouldn't think so. A little background, I'm old school (turned 63 today) and I used to think the cooler the better, but have changed my thinking for a couple of reasons. As long as your running appropriate octane and not running into pre-denotation, the hotter you can run your motor, the more power you will make and better mpg also. NASCAR crew chiefs want their drivers motors running anything over 220 up to 250, course they run 50 psi coolant pressure. On a more relevant personal note, a few years ago I threw the water pump/alternator belt on my 71 chevelle SS due to the A/C belt breaking. I was on a bridge and couldn't pull over until I got home and the temp gauge pegged out, judging by the exhaust tone and throttle response the engine had never been stronger. And yes, after letting it sit overnight to cool, the motor was just fine, alot to be said for iron blocks and heads. just my 2 cents worth. I'll stick with 195 thermostats.

on any computer controlled engine its tuned to run at the stock temp. so if you deviate from that its not going to run right. that being said if you have the ability to tune it you can adjust for lower settings. i think its more about getting cool air into the engine(your intake manifold is at engine temp too), like on my firebird i just have a open element air cleaner and a 160 thermostat, and its carb so i can adjust everything to make more power from cooler air. alot of people ice down the intake too between runs, i dont bother with all that either just usually leave my hood up some

Well said JW, especially the part about popping the hood, underhood temps are killers on belts, hoses, even starters especially during the summertime on modern cars with high operating temps and a/c, many of you may think your battery has been located under the rear passenger seat because of weight distribution or no under hood room, not so, main reason is protecting it from heat, helps with the cold starts too. On hot days I always have the wife back the bonne into the garage,pop the hood, open the side door to garage and hope for a breeze to disapate the heat.

The Gereral has wanted all of his newer engines to run hot 195' to 220'. Then again the General also wants your money every few years, the fewer the better.
The bits a pieces under you hood will last much longer if you keep the temp DOWN. Now there'* a happy medium here by running a 180' thermostat and having you fans come on sooner. Actually the 180' thermostat won't do any better than a 160' because that'* just a point where the thermostat opens.
If the engine is going to overheat then the cooling system is not doing it'* job. Everthing must be right to keep it COOL.
Now a boosted engine needs a lot of help as they tend to run hotter by nature. By reprograming the ECM to allow the fans to come on earleir and stay on longer helps a lot.

Maybe I'm getting one or two extra horsepower out of the cooler engine, but the main reason I did it was because I thought it would add a tiny bit of reliability. Plus, for $10, it'* easy enough to undo.

Keep in mind that changing the temp of the thermostat may not be as easy as just swapping it out. On the 2000+ you may get a SES light because the PCM will think the engine is heating up to slow. Also the fans will not come on until the engine is at the same temp as before. So changing the PCM set points is necessary.

I agree with Dan.

I changed the fan temp settings to a lower temp just to get the fans to come on a little sooner. It helps keep things a little cooler inside the bay when the car is sitting still. Yes, according to my temp gauge, the engine still sits at 195 degrees. But, it won't go past 200 now with the new fan settings.

Don't trust the dash gauges. At 180°, mine seems correct, but from 190-215°, my gauge is firmly planted at just under the 200° line. It'* been like that (at least) since I bought my first scan tool years ago.

My tach is about 200 RPM high, as well, and Dan has spoken out against the oil pressure gauge many times.

The only 100% accurate gauges in my car are the speedometer and voltmeter.

Ooops, sorry, failed to mention, I was scanning this morning on a 4 hour run. 2 hours out, 2 back. I scanned the first 50 minutes of the trip cause latptop battery started dying. Only gauge that isn't accurate is my RPM. Everything else is right on. Including my temp gauge. It stayed pretty much at 196.