Very Little Heat in 2003 Buick Lesabre

It’s a very cold winter in Wisconsin, and I’m getting very little heat from my 2003 Buick Lesabre! The dashboard shows the engine heats to between 155 and 165 degrees F when I’m driving. If I park and idle for a while then the engine eventually heats up to 180+ degrees F (and the heater warms up the cabin nicely). I’m guessing that I have a stuck thermostat, but I was wondering if there could be other causes?

Thermostat could be stuck slightly open. Or it is just so cold the coolant never fully heats up even with the thermostat closed. Some comments here in other threads say the latter can sometimes be addressed by partially blocking the front surface of the radiator until the weather warm up. I’m not entirely sure why this would work, since if the thermostat is closed, no water is going to the radiator. But maybe a little coolant always goes to the radiator no matter what.

From what your’re describing being the issue, the thermostat is the first suspect.


I agree with thermostat. Working correctly, the thermostat will keep coolant circulating in the engine until the target temperature is reached. It will open and close to keep that temperature at that point by letting hot coolant go to the radiator and let cooler coolant get sucked in from the radiator. Temperature rising and falling as you drive and stop is almost always a bad thermostat. Changing out the thermostat is a good reason to change coolant if it is more than 5 years old.

I’d agree that you need a new thermostat.

But assuming the dash gauge is correct, 155-165 is still pretty warm for making heat though. Obviously “very little heat” is a perception thing and full temp (190+) will be warmer. But this is still not cold. So I also wonder whether you don’t need to try to flush your heater core or check out the blend door. If you have any kind of thermometer you can stick in a dash vent, measure the air temp coming out in relation to engine temp.

I’d also ask if the air is actually being blown out of the vents at a good clip. I.e. is the blower fan actually working.

How many miles are on this thing and how often has the cooling system been serviced? (If ever).

Either way, have a full cooling system service done with new thermostat and radiator cap and maybe ask the shop to just check that everything else related to heat is in order.

I’ll go with the thermostat too but you’re into minus 10-20 temperatures and some cars are loose enough that it may be hard getting it up to operating temperature. Try putting a piece of cardboard in front of the radiator and see if it warms up a little faster. It used to be SOP in Minnesota winters.

Those temps are way too low, agreeing with others above! I got a cel Check Engine Light at 5 degrees below for a time in the summer, then replaced theromostat, any CEL?

Classic symptom of a thermostat stuck open. If the heat is ample while parked the blend door isn’t likely the issue. It gets plenty cold here in Canada but I’ve never seen it so cold that a properly functioning coolant system doesn’t generate enough heat.

@Bing … I’ve always wondered why that cardboard over the radiator trick works. If the thermostat is fully closed, no coolant should even flow to the radiator. My only explanation is that there maybe is some kind of thermo-siphoning business going on where warm coolant from the engine cycles back into the radiator from below due to convection (warm water rises), and that makes this work? I think the radiator on old Ford Model T’s worked like that, there was no water pump at all, all the coolant movement though the radiator and engine was all driven by convection currents.

@GeorgeSanJose, big rigs use radiator blankets for the same reason. You will get unintended thermal transfer through the lower radiator hose if the coolant in the radiator is too much cooler than in the engine. This by-passes the operation of yhe thermostat. Temperatures have to be pretty darn cold to affect most cars this way. Big rigs have a much larger radiator capacity, and are much more susceptible.

Turns out 150-165 degrees F is enough to get heat. I took the car to my mechanic (found him through the Mechanic Files), and it turns out my heater core was somewhat plugged up. He flushed my cooling system, and now I have heat. I would’ve sworn I needed a new thermostat – shows how much I know! Thanks for your advice everyone!