Ok so my 1997 xk8 has had an issue since i bought it. When i turn on my heat, it starts getting warm air within a half mile from the house, then it gets nice and toasty for about 10-15 minutes. Then all of a sudden like, it seems like the heat drops down and doesn't usually pick back up again. Ive searched the archives, but usually people have no heat at all. Just thought I'd put it out there for ideas

 

It could be the solenoid sticking .I suggest you unplug it as it fails open. If you can see the pump put a stethoscope on it and you will /should hear it running. The solenoid valve usually cuts off the water when the air con is ON . The pump also goes off. Check wiring diagram at jagrepair.com for the colours

 

Check the reading of outside temp. When it breaks, it shows high temp (120 deg F?) and might turn the heat down.

Check with the temp control on HI. It should bypass the cabin air temp sensor.

Check the "aspirator" by the cabin sensor (it moves cabin air over the sensor for a more accurate reading).

Check with recirc on case there is an air leak with fresh air.

Disconnect the water valve at the firewall. It defaults open and should give you _plenty_ of heat.

Check water temp over OBDII in case you have a faulty thermostat.

Best of luck, keep us posted.

 

So i unplugged the valve and finally got to drive it today! HOLY COW! Constant toastiness! The wife actually commented "wow your car gets really warm!" I told her the whole story too. Ill look into the temp readings at a little bit later date, but for now ill just enjoy the heat!

 

Remember this valve turns off the water when you want to use the air con so you may consider a winter summer switch.
Replacing the valve is a pig.

 

Gotcha. So not to sound stupid, but if something is malfunctioning with the valve, or whatever tells it to open and close, could that be why my a/c doesn't seem to cool as well as i think it should? Like maybe something is telling it to open in the summer when it should be closed? On the other hand, mostof the cars that ive ever owned havent had a water valve and have been just fine. Does this system blow constantly through the heater core? I would have thought the blend doors would have blocked the air from blowing through it anyway

 

There are two circuits . One is for the valve and when it gets 12v it closes and cuts off the water. At the same time the pump is switched off. Clearly for the air con you need the valve closed and the pump off. The pump is almost impossible to reach or even see so be grateful yours is working.

 

To me, it means the valve is just fine, it's been shown to open and close. This is good news ($250?). The pump is best thought as always on, and it seems to work (another $250?). There is a magnetic coupling with the impeller so it does not cavitate when the valve is closed. As you have tons of heat, there is no issue with the heater core or one-way valves, etc. Boils down to the control of the valve. To my knowledge, the valve is cycled on and off by the controller on a low frequency (a few times a min). How many cycles are on vs how many are off determines the quantity of heat to the core. I'd say continue with the tests I listed above and go from there.

Best of luck, keep us posted.

 

Fmertz ..I would like to see some paperwork on the magnetic coupling ...from the dismantle videos I have seen it solid to the motor shaft and i see no evidence it runs 24/7

 

This thread has a lot of detail. This posts shows the pump in some detail.

Heater Pump

The motor basically spins a dry magnet. The impeller resides in a wet housing, with an inlet and outlet of coolant as you would expect. To my knowledge, the motor runs "all the time", as soon as the key is on (engine can be off). The a/c control panel may have to be on for this.

 

Yes, my OE pump was definitely mag coupled.
I intend to pull the relay this summer and see how it goes. Give the pump a break.