I'm having a strange heater-related overheating problem in my 1987 gl-10 turbo. When the heater is off, it runs at about half on the temperature gauge. With the heater on and the fan on 1 or 2, the temperature gauge stays about in the middle. If I turn the heater fan up to 3, the temp. gauge gets up to 1 or 2 bars below red (digi dash) and stays there for 30 seconds to a minute then abruptly drops back to the middle and slowly starts climbing again. With the fan on 4, the temp climbs into the red and stays there. The heater puts out heat, but the fan doesn't seem to be moving much air. The heater isn't near as hot as it was about a year ago, but it is still warm.

My question is, what could be causing this? If the heater core was plugged, I wouldn't expect the heater to get warm at all (or very little) and I would think it would run hot with the heater on regardless of the fan setting. Is there anything I should look at before I take it to a garage and pay big bucks to have it diagnosed/repaired? I've put about $700 into the car in the last month already (4 new tires, leaking intake manifold repaired).

Can anyone explain exactly how the heating system works in these cars? Does coolant flow through the heater core all of the time, or is there a valve that opens when the heater temp knob is moved to heat? Is it tied into the fan speed?

Thanks,

Tom

Bump

 

Maybe just a digidash thing?

i have had the exact same problem in my 87 Gl-10 TurboWagon. I decided its just a digidash thing.. I ran 2-3 extra grounds off the negative battery terminal and the problem has almost completely gone away.. now it just goes up one bar when the heat is cranked up.

 

I know steve was having the same problem when he cranked the fan up to 3-4 with the AC on. He also has an 87 GL-10 TurboWagon

I also agree its a digidash thing. It seems the more power drawn from the system the higher the gauge reads. But you also say the fan isnt moving much air either. I would check your ducts, make sure there arnt somethings in there plugging them(mouse nests and such).

Rob