Hi guys just joined so not to sure what I'm doing.any way I have a jag xj8 2001.when I'm driving the heaters are nice and hot when I slow down or stop they go cold.temperature is normal.pump was done 4yrs ago.could this be a internal heater matrix partial blockage. If so this would me a reverse flow flus. Now has any one know what else the problem could be plz .

When you say the pump was done 4 years ago are you talking about the water pump or the Auxillay pump which is used to augment the water flow at low RPM?

Heater problems can be normally 3 things:

1. Blocked matrix; will get some heat at idle, but getting colder if driving,
2. Aux. pump; will get colder at idle, but getting heat if driving,
3. Interior sensor; generally only getting heat with button at MAX.

I should suspect the pump again, especially as a blocked matrix should not give you much heat while driving.
First check; just lay your hand on it with key in pos II, it should vibrate.

Hi rob the main water pump on engine.why is there another one as I've never had a jag and only familiar with other vehicles.

The x308 has an auxiliary heater pump, to circulate coolant if the rpm's are low.
This pump fail if the brushes are worn, do a google and you will see what happens.
You can repair the pump with new brushes, or buy a new pump (where a Bosch pump is wayyyy cheaper than the original Jaguar one).
https://www.jaguarforums.com/forum/x...3/#post1795189

Hi all thanks for your help.well I can here tge pump prime when I turn ignition on quite loud it is..

Are you sure you don't hear the throttle body, the aux pump doesn't make noise (or should not at least).

PS. On a LHD car, the aux pump is on the left side, tucked between the wheel well and the engine, reachable from the top if you open the bonnet.
Not sure on a RHD, maybe same, maybe on the other side.

Hi it may very well be. It sounds like an electric aerial noise.

Locate the pump, feel it with engine off and key at II, then you know.

RHD car has the aux pump in the same place, the mag retrival tool is pointing to the end of the pump, the water flow is regulated by a solenoid valve so minimal fluid should escape.

Hi guys I have taken the second pump off car today and tested it and it's dead.so I have stripped it down and the brushes have gone but I can't get the motor end through the body.any suggestions. Plus were can I get the brushes from.I can post photo but can't fin how to do it .if any one can tell me I can post thanks u

The link below is for the brushes sourced from the US . Ensure you order 2 . They're a little long and can be filed to fit . European and rest of world source ? Can you elaborate on " I can't get the motor end through the body " ? If you pull the impeller housing off the common rubber O - ring is probably swelled and can't get it back in and a new one can be sourced from the hardware store . I have an extra one somewhere to get you the size if I can find it .

.15" x .15" x .35" BRUSH 33A

To post a photo go to the go advanced icon and then the manage attachments icon then pull from choose file icon hit the open icon then the upload icon , give it some time to upload . The last thing is the save changes icon .

Good you found the source.
This one will tell you more than you will ever need:
Heater pump repair.
If not, there are plenty of other threads on the subject, easy peasy with google or the in-forum search function.

Hi guys thanks for all your help I will up load photo so you can see what I mean.thanks.

Great to read this thread and know about the secondary pump. I'll put that in my file.

In my case, I think I may have a bad interior sensor. Any thought or advise on how top replace it?? Thanks for the help!

The interior sensor gets very very very did I mention very dirty and unresponsive , just a good cleanup from the backside is probably all it needs . To remove it you may have to remove the lower kick panel as mine is a X300 series , same setup .

Thank you Lady P. I will pull the sensor out this weekend and give it a good cleaning. I'll probably use some MAP Sensor cleaner and compressed air.

MAF cleaner may remove the oil in the fans motors bearings , yep it's got one . A dry brush works fine . Important is the thermistor bulb you will see that you leave no oil on it . Inspect , clean and protect the connector .

Good advice! I will be careful in my cleaning.

Hi rob I have fitted a secondhand pump .I did test it b4 I fitted it and all good. I have sat in car and started it got it to temperature and heaters still freezing cold .fine if you drive it but no heat at standstill what else could this be.thanks