Heater blowing warm then cold then.....?

[sandman]

I have a weird heating problem. Driving down the road the guage will go into the read and then drop back down again. I searched and saw that this could be a result of the digi dash. OK, I can live with that, but it does it in junction with how the heater performs. It will put out warm air and as the guage goes up, the heater starts blowing cold air. I'm guessing that the water pump must be dying but I'm looking for other input as I just finished changing out the oil pump seals and would love to tear apart the front of the engine again.

 

This is on an '87 GL10 Wagon Turbo.

 

Thanks.

[Subi81]

Could be a termostat problem if the temperature is being effected? maybe someone out a low temp themostat in there?

[mcbrat]

my dad had that problem. his thermostat was stuck open....

[Turbone]

Make sure you replace it with a OEM thermostat.

[idosubaru]

AH! always assume it's overheating unless you're positive that gauge is inaccurate. heat is too damaging to mess with.

 

these guys got you on the trail, replace that thermostat. have you drained any coolant lately? it's doubtful, but you could have some air pockets in your cooling system.

 

questions:

any coolant loss?

any coolant leaks?

is your radiator old (possibly clogged)?

has it ever been flushed?

 

this should not cause overheating but can easily cause no heat, so i doubt it's your problem but if you're looking for something to tackel - pull your heater hoses out (should have hoses going to your firewall for heat), pull one out and blow it out with a water hose.

[Skip]

check the belt tension first

[thealleyboy]

The "hot-cold" condition could also simply be caused by low coolant level.

 

All the suggestions offered above are good ones. Just go thru the system meticulously, testing all the components along the way. The t-stat, and rad cap are two likely culprits.

 

good luck, John

[sandman]

I'll go with the thermostate first but I really think its the water pump.

 

The car was fine untill this problem gradually started. I begane burping the system and it seems to be topped off although an air buble could still be doing this. I dont think its the thermostate as the engine is hot and the heater so not putting out any heat. It was my understanding that the heating circute was behind the thermostate with the engine.

 

I'll spend some time this morning doing some burping on the jackstands and see what happens.

 

Thanks for the reply's.

[WJM]

cant go wrong replacing the t stat AND doing a fresh coolant change.

[sandman]

OK, I was in the process of trying to burp it when I noticed that the waterpump pulley was vibrating around pretty good. So I said to hell with it and pulled it out. The bearing in it is totally shot. The whole shaft is loose and when you turn it by hand, you can feel it grinding away. So, new water pump, radiator cap, and some fresh coolant. I'm going to go and put it together now and see what happens.....