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Heater Question

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Grady

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I've a '95 XJ6 and while the auto a/c seems to work fine I discovered this week that the heat doesn't come on, only cold a/c. At the same time, I noticed that my temperature gauge hardly moves off the C of cold.

My thought was it would be some kind of sensor related problem but my post on Piston-Head brought back a number of "bad thermostat" responses. That seem unlikely as the car isn't overheating.

What do you all think? Thanks Grady
 
One of the possible issues is not enough coolant either getting to the heater core and also the temp sensor. You could be overheating the lump and not know until it's fatal. Check the fluids fast before you melt the engine.
 
I agree. Start by checking the coolant level.

Next check the vacuum controlled heater wvalve to make sure that the vacuum line is connected.

With engine at temp, outlet side of valve should get warm when the valve is open. Check the feel of the temp on both sides of the valve to see if it feels the same.
 
> ..."bad thermostat" ... That seem unlikely as the car isn't overheating.

A bad thermostat could be stuck open so the engine does not heat up.

The symptoms would be exactly as you described - no heat and temperature gauge reading too low.

It is an easy and worthwhile job to change the thermostat to be sure.
 
I never thought about it failing open - most of my problems have been with them failing closed. Got an new one and will install tonight - and the coolant is full. Thanks Grady
 
Hard to believe something so simple could lead to a broken bolt ear. Anyway one thermostat housing later, all is together and the temperature gauge seem to work again - but not the heater with or w/o the compressor on.

Next I'll try the vacuum controlled heater valve.
 
Anyone have an idea on how to test the water (heater) valve?

It a very interesting piece of Denso valve work and I think it may be my problem with the heater. At least the hose is cold on the far side.

But vey expensive for a test of a new (used) one. Grady
 
re: XJ-S V12 Heater valve - MIGHT be similar to XJ6

Autozone part #5939 is the exact replacement for the OEM V12 valve for $53.

Factory Air Part #74803 is a plastic replacement for $15.

I used the FA valve in my XJ-S and its been working for 5 years now. IIRC, the vacuum hose size was a slightly different diameter.
 
Thanks for the suggestions, I think you may be a vacuum valve as was suggested above. Mine is an electrical (solenoid-type) valve. I found one on eBay so we'll see...

It's about time for the weather to warm up here anyway. Grady
 
IIRC, your car, like many other newer ones, does not have a heater valve. Coolant flows through the heater core at all times. Flapper doors control the air flow. I don't know if your flappers are controlled by vacuum or electric, but that's where I'd look.
 
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