One feature I really like about my '00 LeSabre is that the temperature gauge setting will show an actual number for engine coolant temperature. It'* made me aware of a possible problem anyway.

How hot should the coolant get when at full warm on these Buick'*? Mine has a hard time (or takes a really long time) reaching 150 degrees which seems pretty low. I would think these cars would run around 160-180. It hangs out in the 140'* during my daily commute, which is about 15 minutes of mixed city/highway driving. Should be plenty of time to get the engine to full operating temp I would think.

While a cool-running engine usually seems fine, 145-150 barely gets the HVAC heat blowing lukewarm air. It has been COLD where I live (right now -3 with -22 windchill) this winter! I have to leave the heat setting on HIGH constantly, just to barely (and slowly) warm the inside of the car. Air is noticeably warmer if/when the engine temp reached 155-160, but that has been rare.

I topped off the coolant level last week, so that'* fine (it was a bit low when I first noticed lack of heat). I'm thinking possible problem with heater core, but first I wanted to get a consensus on engine temps.

thermostat is stuck open, stock temp is 195, should come up to temp fast (within a few miles) and stay there even in this cold

Lower Intake Manifold (LIM) gasket failing is the most common reason a 3.8L or 4.3L GM engine runs cooler than it should. Replacing the thermostat typically masks the issue for a few days, them back to cooler running temperature.

You may want to do a cooling system pressure test.

While gasket failures are common, the first thing I would look at when the cooling sytem is not coming up to temperature is a failed thermostat. Replacing a failed thermostat does not mask the problem, it fixes it.

Always start with the easy stuff first.

i would think it would make it run hot more than cold. but neither my yukon nor my bonnie(either time of twice) made the temp do anything different. just got misfire codes and ran like crap. i have however had a number of stuck open thermostats over the years and it always made the temp do exactly as he states

Roy/ Justin,

Can't explain why, but on the 3.8L and 4.3L, with a failing LIM Gasket in a condition of not getting up to operating temperature in the winter, any changes to the cooling system mask the real issue for a few days. Change the thermostat, heats up good for a few days. Change the water pump, heats up good for a few days. Then the issue returns. Makese no sense to me, but I have seen it numerous times. Change the LIM gasket and no more issues with not running hot enough in the winter.

Post #10 and #13 of this thread is a good example of the above issue:
https://www.gmforum.com/chevrolet-17...-issue-306133/

guess it would be accompanied by coolant loss that you cant find

Or, it could be a failed thermostat. I like to start with the easy stuff first.

Well here'* what I can tell you all for now... I replaced the thermostat today, and the temp is much more normal (180'*-190'*) now after a full warm-up. I will say that it still took a good 5-10 minutes of idling and 5 minutes of driving to get the temp that high. Heat is working great for now. I'll see what happens the next few days.

I did notice a bit of moisture on the bottom side of the oil cap (I'm talking a few clear drops), and a bit of gunk that came out of the radiator when I pumped out coolant for the T-stat change, which I then later dumped back in. Here'* a couple photos of the residue left behind in the jug, after I poured the the coolant out... anything suspicious, or just typical brown Dexcool buildup?

One more bit of strangeness... the old thermostat appears to function properly. See images. It was closed at room temperature, and opened after I put it in water and boiled. (That was a test I always wanted to try and never had before.) So I'm not sure what the problem was when this thermostat was still in the Buick, since it'* working now...