Odd '97 GT Heater Problem

[r_willy]

Got something strange going on with the heater and/or cooling system in my '97 GT wagon. A few weeks ago, I noticed I wasn't getting any heat after the typical amount of morning commmute time. Watching the temp guage, it would climb above the mid-point (which it has NEVER done before) and then drop suddenly. My two-bit diagnosis was the thermostat, so I swapped it out and am having the same symptoms. Sometimes you get warm air from the vents and then the air temp will get cool again. I'd suspect a door in the inside/outside air ducting was stuck, but then I go back to the weirdness with the temp guage. Is there something besides the thermostat in the Sube cooling system that regulates coolant flow? The system was flushed and refilled last fall, so my list of the obvious cures is pretty short. Thanks much!

[Reason]

How many miles? You could have blown head gaskets. You can do a compression test (cylinders)or chemical test (coolant fluid). 2.5's are known for blown HG's.

[NewGenSTi]

Sounds like a bad thermostat to me.(edit) sorry didnt read you replaced it...

[NewGenSTi]

there is a heater control valve I believe too but its a dealer only item could be the problem. but I cant see that causing your temp to go over midpoint. the thermostat should be opening around 170. if you replaced that it doesnt make sense really Are your fans working as well?

[r_willy]

How many miles? You could have blown head gaskets. You can do a compression test (cylinders)or chemical test (coolant fluid). 2.5's are known for blown HG's.


Car has 93k on it.

Arrgh . . . hadn't thought about a head gasket! But would the coolant temp go down as well as up? About time for an oil change, so I'll see what comes out of the pan. In the meantime, I'm open to any less-dramatic diagnoses out there!

[r_willy]

Are your fans working as well?


Wondered about this one -- fan thermostat maybe? When I was refilling the rad after changing thermostats, I watched the fans to see if they were running when the engine came up to operating temperature. But could they move enough air to cause an obvious drop in air temp coming through the vents when the car is thoroughly warmed up?

[Reason]

When my T -stat went (at around 85k miles) The readings where up, down middle. Hot air blew out, cold air blew out (when set on heater). I changed my T stat 4 times. Not sure what brand the first one was, but 2nd 2 where auto zone specials and 1 Subaru. Radiator flush twice and new coolant. New water pump and timing belt. Then said eff it and went to Subaru. Compression was low and my coolant had oil in it. They took it apart and showed my the coolant in the cylinders.

Do a compression test and chemical test before you spend money are parts you may not need.

[Kelly]

Uh oh, 93K on a 97 DOHC. Bad news reguardless.

Easiest way to check for headgaskets, stick your nose right in the coolant resivoir bottle. I mean really stick it in there, get it nice and hot, and rev the motor.

If you smell exhaust, you gotta bad head gasket. Probablly drivers side.

The heat just doesnt stop working without an air bubble. Possably a bad rad cap, but I've never seen a DOHC gasket make it past 100K.

[Legacy4Life]

Well there's lots of explinations for possible head gasket issues, but at 93K that's pretty low mileage. Unfortunately I'd have to say that a head gasket is a good explination for what you're seeing tthough. It will presurize the cooling system and you won't get flow through the rad. That will drive the temp up inside the block. As soon as it flows again it will drop but then it can rise again.

It's definately worth having this possibility looked into ASAP because a head gasket doesn't go away, it just get's worse... fast. You don't want to damage anything else, plus is oil is getting in the coolant that does wonders for the cooling system too!

And by the way, this is the experience speaking of one who waited too long on his car! :( Although mine has 250K on it at the time.

[r_willy]

Just to put a cap on this thread -- dealer confirmed a leaky head gasket. They advise rodding-out the radiator when this is done as deposits apparently contribute to the problem and can't be remedied with the routine system flushing. With the engine out, the list suddenly got much more complicated and expensive, going with timing belt and misc. hardware and seals from the front of the engine as well as clutch parts and flywheel (can't resurface the flywheel -- nice!) at the back. Presently bleeding from every orifice but it looks like I'll own this car for a few more years -- now.

Thanks for the excellent diagnosis and discussion -- hope this serves someone else as well.