Actually it is the thermostat. There is gunk in the radiator, as I found when topping it off. My guy suggests waiting for warm weather so the gunk is softer and can be flushed out. Then he'll replace the thermostat also.
Maybe the door is broken too, because the coolant temp was normal before and there wasn't much heat then.
Crap in the system... NOT good. Try an reverse acid flush on the heater core. If he has a flushing machine it would be an easy option. Or DIY with the proper cleaner and a small pump to circulate the cleaner.
Easy check for the doors. Switch to floor heat, turn the fan to high. Cycle the temp control. You should hear the fans tone change as the door moves from hot/cold/hot. You may also hear the door itself because the fan will tend to force it closed to either side.
So that's a "no" vote for waiting, right? He said flushing it while it is cold and viscous will just get it stopped up worse. Or, I realize, the temperature reading might be wrong because flow is already restricted.
If a bad thermostat makes it run so cool, then there must be feedback. How does that work? Just by controlling the fan, or part of the circulation?
Not sure how waiting till it's warm is going to change anything. You need to start the engine, drive the car to the shop then wait for it to cool down before you can work on it anyway. Unless you are working outside in the cold it's not going to make any real difference.
The system looks at the coolant temp, ambient air temp, intake air temp and looks at a chart that basically says something like "If the outside temp is 30 degrees, the intake air temp. is 30 degrees and the coolant temp is 30 degrees it should take the engine 8.3 minutes to reach operating temp. of 195 - 220 degrees."
The heater core isn't monitored. In your case you say the engine does warm up when you were stopped but that it was cooling down while driving. Once the temp crosses the operating temp the ECM assumes it will stay there with some fluctuation.
If the engine cools down the thermostat closes down and reduces coolant flow, raising engine temp. The actual passage in the thermostat is also designed to restrict flow once the thermostat fully opens. This ensures that the coolant dwells in the block long enough to transfer the heat from the engine into the coolant, preventing steam pockets.
If the engine starts heating up it turns on the cooling fan(s)
If it's the door you'll have problem on the other side too, when it's time for A/C. Mixing other brands of anti-freeze with Dexcool can gunk the radiator. So can putting stop-leak in the cooling system. I wouldn't wait, because with the 3800 on that car it could be a leaking plenum or intake gasket. Pretty common. Don't know if those would gunk the system with oil.
And on some years, the intake leak would let coolant run onto the cam, washing the oil away. You then have a round cam lobe.
It has a slight leak, but the head of maintenance at the Buick dealer talked me out of fixing that because the car is 12 years old and he said it might open a can of worms.
Another great place for plastic.... Some day's I'd love to find the engineer and the bean counters that made the decisions on some of these things...
Plastic snap in coolant transfer lines, Those lovely POS heater connections, Plastic intake manifold, right next to the damn EGR tube, NAA that tube never gets that hot....
Bad advice.
Agreed. Not fixing it could cause a bigger can of worms. Much bigger.
Have you looked at the inside of the oil cap?
"GM Sweats the Details"
I could tell you stories...
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.