A couple weeks ago my heater would only work if the car was in motion. Then, a couple days ago, it doesnt work at all. Nothing but could air. Now, last night, my temp was getting a little too close to the H. Is the thermostat stuck shut? Anything else i should look into while i replace it?

 

thermostat and a Prestone Super Cleaner flush. if the thermostat is locked you usually still get heat (depends on the car). Pretty sure you have a nice buildup in there so teh supercleaner will free it up.

 

When was the last time your serviced your cooling system?

I doubt it is the thermostat but when they fail they fail in open position (stuck open). When the coolant indicator does go high, when does this happen, under hard acceleration or always.

I would suggest draining the radiator and seeing if the flow is consistent, the flow should be fast and then trickle down towards the end. If the drain is slow you have a clogged radiator. I would invest in a good after market radiator also send the present oil for analysis, it could show if your head gasket has been affected since your vehicle has overheated a couple of times!!!.

 

They stick in either position.

 

Absolutely not true.

By design, as the temperature sensitive spring gets weaker, it opens sooner. Also by design a thermostat door opens in the direction of coolant flow. This is all in place so as the thermostat ages, it doesn't make the enigne run hotter.

A thermostat installed in the wrong direction will cause an overheating condition as it gets older because the spring will not be able to pull the thermostat door open against the flow of coolant.

 

tell that to the tons of cars who have suffered from overheating due to properly installed thermostats that would not open.

 

All the t-stats that have gone out for me typically stay stuck open, not once had one stay closed.

 

machinehead: If you are on the original radiator, I would look at the radiator first before going to the thermostat.

First exercise: Open the radiator cap and check the flow from right to left, once the thermostat opens you should see a flow from right to left where the upper hose is connected to the radiator. If there is intermittent flow, you have a clogged radiator.

Second exercise: I would do a simple drain of the radiator and look at the flow as explained above, nice flow is essential as soon as u open the radiator drain plug. If not you have a clogged radiator.

 

Heat really has nothing to do with the thermostat coolant runs through the heater core whether the thermostat is open or not.

It could be low coolant Ive had this problem before when I would rev up the engine the water pump would spin faster and the heat would work and the car would not over heat. But when I was idling the heat would stop and the car would overheat due to the lack of coolant in the system. You could check the coolant level but I hate to say it it most likely is a clog somewhere.

 

Here is what I would check (recaps what others wrote above), in this order:

1. Air in the cooling system (or low coolant) can cause overheating and lack of cabin heat. Is your cooling system full? Any air in it? With engine cold your radiator should be full to the brim. Is there any coolant in the plastic overflow tank?

2. A clogging cooling system could do likewise. If #1 checks out ok then drain your radiator to inspect what comes out of it, noting flow rate as Love... wrote above. Refill, get the air out, and follow Love's suggestion above to check for flow. If there was any goop a flush may be in order. If the flush doesn't work you may need to replace the clogged radiator, and (better hope not) the heater core.

3. Thermostats usually stick open when they fail, making the engine run cold when you have a headwind (i.e. moving at any speed), and take longer to warm up in the first place. I haven't seen overheating from a failed OE thermostat installed correctly but anything is possible.

4. (This is a repeat of warning above) If you have overheated the engine several times you may have compromised the head gasket!

 

YES! this is all good advice. check for air in the system (empty overflow tank, gurgling sound under acceleration, low coolant level in cold radiator, etc) -- trapped air will absolutely cause poor heat & hot temp gauge. purge the system of air before doing anything else.

check out this thread for a recent adventure into the world of clogged heater cores....
http://forums.maxima.org/showthread.php?t=502762