Any ideas on why the the car won't blow hot air at idle. Once I get going it starts to heat. However, once back at idle - no heat. Kind of a bummer since its been cold lately.

My 98 Vanden Plas heat is awesome. its like night and day between the two. However, the XJ8 is my daily driver and better overall.

Appreciate any thoughts.

 

These models are equipped with an electric heater pump which is mounted just below the expansion tank.
This will not operate until a certain coolant temp. is reached and then circulates the coolant through the heating matrix inside the car.
There is also an electronic valve system sited just below the pump.
These two control the fluid flow.
Seems strange that you start to get heat when on the move but not at idle, which tends to rule out faulty thermostat.
Do you know when was the last time the cooling system was serviced?
Have you gone through the full functions of the heating system including while on A/C?

 

Start the car and set to the highest temp at idle. You should feel the heater pump running. If not, check for voltage at it's connector. If you have power, then the brushes are probably worn. If you are handy you can replace them. There are threads that show how. You purchase slightly oversize brushes and file them to fit and solder in place. While it is out, you can test the flow with a bucket of water.

If the pump is working, if may be the heater valve, but is more likely one or both of the one-way valves.

Of course, make sure that the cooling system is full before doing anything else.

Good luck.
Bill

 

Thanks!

Coolant is good and was replaced when the engine was removed 500 miles ago. I also just replaced the reservoir which was leaking where the sensor plugs in. Also, the A/C was inop, but had the temp sensor replaced and everything's working fine with that. I also replaced the right blower which had seen it's last days. Other than that, nothing else done with the heat or A/C.

Is this the Part your referring too? I don't know if this is considered the valve or the pump. Doesn't look too hard to get to. I was thinking if that's it, I could swap it out with the parts car I bought. Then as mentioned, fix the other one if the brushes are bad.

The manual didn't seem to have much on this guy. At least what i could find.

 

Yes, that is the heater pump. When running, you will feel it vibrate. Double check yourself by feeling it with the heater switched off.

 

Thanks! I'll check it out when i get home tonight.

 

Heater pump is getting power. Doesn't feel like it's vibrating. If it is it's very subtle compared to my other car. Seems like that could be the problem. I'll have to swap it and update afterwards. Thanks for everyone's help so far.

 

It's been a little while, but I wanted to update. Today I swapped the heater pump with the one from my vanden plas. Works great now!!! I finally have heat at idle. Now, time to dissect the non-operating pump and swap brushes if needed.

Thanks again everyone for your helpful input.

 

Before we close this thread, can I ask a somewhat related heat question? Why does my heat cut out when I am clicking along at 50 or 60 mph in cold weather? Water pump and thermo are new in the last year or two. A/C steadily blows cold in the summer. Usually I shut if off, wait a few mins, and restart and heat will resume.

Ideas?

 

When I replaced the brushes on my heater pump, I used these brushes.
They had to be filed down to fit, but not too much.


Good luck
Bill

 

Looks like they're sold out. I had to order form SourcingMap. Hard to find in stock for some reason.

Did you cut and resolder the wires or did you add connectors for easy replacement next time? I was thinking connectors would be good.


Dan

 

I cut out and resoldered in the new pigtails.
My car has 77000 now. I expect the brushes to last at least half as many miles more.
That will be a couple years until I have to do it again, if ever.

Bill