I have Jaguar 01 XJR with no heat, yet after running for a while and driving on the highway on a cold day the heat works, yet when i come off the highway and run around town it blows cooler air. Sounds like aux pump is working but haven't tested it yet any thoughts on what else could be the problem. Doesn't car overheat and coolant temp gauge stays in the middle. Any help appreciated

 

The motor in the aux pump might 'hum' but the impeller might not be turning?

I flushed a few heater cores when I worked at the dealer.
Jaguar issued a TSB for the earlier sedans.

I used some clear 'poly-tubing' and some HOLTS flushing chemical.
Let it soak overnight.

 

To make the heater pump more understandable, what Bob said was true. The pump can hum and impeller may not be. How is that? The impeller turns via magnets. The impeller isn’t physically connected to the electric motor. Just today I flushed my heater core with white vinegar. Pay attention to what comes out of the core when you flush it.

 

Okay im going to give it a try and see how I make out thank you for the feedback

 

check pump

otherwise do a full flush of the cooling system with CLR

 

If the impeller gets clogged, the motor will be turning but the impeller will not. If you get the pump out, it is easy to detach the pump head with impeller and inspect/clean it (see the attached document).

 

This is the electric motor side with the magnet.

This is the backside of the impeller to show it’s not physically connected to the electric motor.

 

I am having a similar issue myself. Feels like the heat is only partially hot. My aux pump is spinning but since it’s a mag drive possibly not pumping so I need to dig into that.

 

my pump does not work and it blows the fuse. Cannot find it here pump!
ryejag

 

Under the hood drivers side right near top of wheel around there, fixing mine over Christmas break.