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Well, here's the deal. Im driving. I have the heat on, and the engine temp on the dash is one notch below red. I turn the heat off, the engine temp drops to

about half. When I turn that gosh darn heater back on, the engine temp rises.

 

 

It scares me because when the heater is on it will sit at one notch below the red. I'm not liking that. My 21 year old Subie probably doesn't either.

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If you mean "turning the heater fan on" and the temp rises, I would *suspect* an electrical "issue" rather than a temperature issue.

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You have the digidash right? Me too, mine used to jump up hugely when I would turn my AC on, (yeah yeah I know its the ac not the heat) but right when I turned it off, about 3 seconds later, it would drop back down about 3-4 notches, so clearly it wasnt true that my coolant would heat up instantly and then cool off instantly. the digis are known to be sketchy when it comes to accuracy of the sensors.

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It's not the accuracy of the sensors, it's the solder joints on the digi-dash circuit boards. Just like the sketchy EA82 clocks, the solder they used had a lot of flux and they appear to have not been heated enough to burn it off. The joints crack away from the board and the connection is crappy. Different voltages through the bad connections result in different readings as the amount of resistance from the poor connection changes the voltage drop across the circuit.

 

GD

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My old digi dash did the same thing. It may be the dash, but check a couple of things. CHeck the alt output. CHeck the electric cooling fan and make sure the bearings are good.

 

Mine was a bad auxiliary fan, drawing too much current, pulling down the charging system.

 

 

nipper

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The screwey temp gauge problem, as I understand it, stems from either a bad ground on the gauge on the digi dash, or at the temp sensor itself.

 

Do you have a GL-10 or RX? If the car is a turbo, and you haven't already done so, you MUST (my command) replace the radiator with a dual core model. I blew two head gaskets, and several coolant hoses before I buckeled to someones advise on the board to do so. It will save you many $$$ on towing and parts for blown head gaskets.

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