I never checked heat when I purchased my car in April. I replaced all of the coolant hoses, flushed out the system and replaced the coolant. I did the bleed per the service manual, but I only get slightly warm air (on a warm day). I did unplug and remove the auxiliary coolant pump for the heater but put it back in (and am quite sure I plugged it back in correctly). My old X300 pump brushes went out and I had to replace them. Does the heater pump go out on this car fairly frequently? Is it the brushes? And is there a way to test/confirm if the pump is working (other than taking everything apart to get to it)? On the X300 it was openly visible and easy to work on. This one in the X350 is not really accessible from below, and you have to take all the hoses off to get at it from the top. Pretty much impossible to jump the pump to test it.

Or is there anything else I should check?

 

The aux heater pump is only really needed for idle and slow speeds, otherwise your main coolant pump should push enough to get heat. Especially in warm weather, there should be plenty of heat. I do not believe there is a heater control valve to stop water flow on these models, so the only other thing is a clogged heater core.

I think there are some old posts about this issue, you might be able to back flush the core to get it working better. You can test for this by feeling the inlet and outlet of the heater lines, if it's clogged the outlet will be much colder than the inlet.

 

Does it cool down OK ? Reason I ask is because the climate control system has fan control module sitting on top of the fan behind the glove box, and these are a well known failure point.

So check the climate control fan works. Of course the heater matrix may be blocked as this is another of the failure points.

 

When I changed all the hoses and flushed everything recently, I seemed to have decent flow through the heater core (when flushing). I will check the temp of the inlet and return and see if there is a big difference, although based on how it was flowing during flushing, I don't expect a big difference.

 

AC works great, blower works well, etc.

 

On my 3.5L V8 I can reach down and feel that the aux pump is running by the slight vibration but this may not be the case on the 4.2L engine.

I suspect that when the heater core gets blocked or partially blocked you can still get a good flow rate from the outlet but the core is short circuited.

Measuring the in and out temps should reveal the truth.

I have a little laser temperature gun (incredibly cheap ex Hong Kong) which is ideal for checking temps.

 

Please can anyone confirm the location of the heater circulator pump on my 2004 XJR. I cannot locate it. I have found the supercharger pump, and confirmed the heater pump blows fuses, so there is an issue looking for resolution.
thanks
Rye Jag

 

The Xjr Aux heater pump is in the right hand front corner of the engine bay. It is at the chassis rail level but unfortunately in the middle of a rats nest of pipes. The supercharger pump is very well hidden and I suspect you may have found the Aux pump and not the supercharger pump . The supercharger pump need the front bumper removing to get access to it, its at the front next to the radiator.

 

Joe

you are totally correct, I found the Aux pump and didn't know it.

Best wishes and thank you

RyeJag