Heater / Cooler / Thermostat help

I’ve got a 2000 Subaru Legacy Outback. The blower for the heater/cooler works, but the temperature doesn’t change no matter where the dial is. Most of the time it’s just cold air blowing out, but for a few days out of the month, it is hot air only. Sometimes it’ll be hot air for a day or two in a row, then it’ll go back to cold air for who knows how long. I haven’t been able to see an exact pattern. The engine temperature guage in the car is always normal. Heats up at a regular pace and sticks right in the middle.

Can anybody offer any advice and what I can do, before my mechanic tells me I’ve gotta spend 500 bucks with him to fix it?

Is this a thermostat valve problem? Thanks for your time.


We service a lot of Subarus at my shop, and we’ve never experienced this problem.

If your gauge is reading in the middle, then your thermostat is working.

I would suspect two possibile causes.

First a problem with the mixture control. The mixture flap may be broken, and getting flopping between full cold or full hot. Or the control operating the mixture flap could be broken.

Second, your car has common head gasket problems. Subarus solution to fix this, was to inspect every car, and it they were leaking externally, pull the engine and replace the head gaskets. If they aren’t leaking, flush the engine and put stop leak in to postpone the porblem. Stopleak is bad stuff. You put stopleak in a $500 car that isn’t worth fixing, or in a crisis situation. Stopleak floats around in your cooling system and can plug up a cooling passage instead of a leak. If your car has had that dealer campaign performed, it’s possible the heater core could have gotten plugged up. Reverse flushing the heater core most frequently will take of that.

there is another valve to have trouble shot.

there is a diverter valve which either turns on or off the radiator water loop to the heater core. (this is used when you have the AC on, it shuts off the hot so the AC can run full) this valve is located in the line of the heater hose, usually just before the hose goes through the fire wall into the passenger compartment.

try this test; turn on the AC does it blow cold, or is it intermittantly hot then cold. thats the valve sticking. have you had problems with the AC last summer, not blowing completely cold? same problem. same solution. put in a new diverter valve.

if you cant trouble shoot this yourself, go to a radiator shop, they can fix it alot quicker and cheaper than a dealership will.

also, you should look over the receipts for the previous mentioned warranty work if that was done. that may make a difference in the diagnosis. (and the cure)

Thanks for the help.

Thanks, I’ll look into these.