Ok my Mom'* Park Ave the temp was running about 201-205 degs so I chgd the t-sat with a new recommended 195 and it stayed the same. So.. I went to a 180 stat and now it runs about 180 - 183 with an outside temp of about 56 degs. My question is this, is that too cold for this engine to run for best gas mileage ?? What will it run in the dead of summer ?Thank you

where are you located?

i run a 180 year round, works great. if your engine doesnt get up to temp in a certain amount of time, it will turn on the check engine light. If that continues to happen it might be best to put the 195 back in.

We live in Central New York State, what do you mean if it doesn't get up to temp ? Isn't 180 up to temp for a 180 t-stat ? The 195 was keeping it over 200 degs . The digital readout in the dash says 181 degs "normal" is this * problem ? I drove it about 200 miles today and no CEL. I'm confused what does yours run with a 180 stat ?

mine runs 180-185 with a 180.

the problem i mentioned that is during cold winter temps, if the engine does not get to 180* within the first 10 minutes (just a guess) of running, it will throw the CEL - DTC P0128 Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

dont be worried about it unless it happens

That doesn't sound right. On mine, it stays between 185-189F on an 80F day in stop and go traffic. On the same 80F day it'll go down to 176F when it catches a lot of air like on a freeway. It will hit 200F at times, but only in triple digit heat; and even then, it'* just for a short period of time.

You may be wondering why mine stays so cool. Well, I change out the Dex-Cool every 6 months and mix it 50/50 with distilled water. Some people will say that'* overkill; it may be however, but I never have to worry about my cooling system staying cool. I also check to make sure there'* no bugs stuck to the radiator. I use a 195F AC Delco thermostat.

There are alot of factors. Condition of the coolant (DEX goes 'sour' over time), condition of the radiator, was the AC on (if it is, the fans are on), and the condition of the coolant sensor.

The best bet overall is to drop in a 180 stat. Do that first, then we'll go after any issues that may remain.

Ok I have kept the rad flushed out every 2 years and used Dex compatabile antifreeze. I did switch to a 180 stat this week and it now runs 180 - 183, but the weather here now is only in the 50'*, when I was running the 195 a week ago it was 80 degs. So, is 180 - 183 in 50'* temps too cold or will it rise when it is hotter out ? I saved the 195 it is a Stant t-stat but if you think I should I could go to a GM dealer and get a 195 I will. My brothers Bonnie runs around 205 all the time I just wanted Ma'* running a little cooler but maybe its not a good idea. She does pull a small trailer with a garden tractor sometimes.
So I guess the real question is , is 180 degs too cool to run that stat ? Thanks guys !

Oh yea, the a/c/ on or off didn't seem to make a diff in the temp.

The temperature gauges on the 00+ Bonnevilles are not very accurate, and do not vary like previous years. If it was, you would be able to tell as the car warms up when the thermostat opens, and closes by the temperature variation. From what I've read on it, many customers became concerned by the swings of the gauge, so GM designed it to hold pretty steady around the 200 mark. It may be just a little above, but usually just a little below.

I run a slightly drilled (1/16th) thermostat in my car year round without an issue, and it gets pretty cold here. The only time I had a problem was when I had 2 larger holes in it, and that was just in the winter. You should be fine with the 180.

Unfortunately, oil pressure gauges in other GM models have fallen victim to this. As long as some cars have over 6 or 8 psi oil pressure, they just read a "happy medium", which is as bad as an idiot light.

so leave the 180 that is showing 180-183 on the digital readout ? The 195 was running at 203-207 on the digital readout in the dash. I towed her trailer with her John deere garden tractor on it and outside temp was 57 degs and it held steady at 181 degs