I had a similar problem with my 1999 XJ8. I had coolant running everywhere and at first I could not trace the leak. Odds are either your thermostat housing is shot (it's a composite plastic) or the bottom housing seal has failed. Best thing is to remove the plastic ornamental covers that go over the valve covers, start the engine and see where the coolant is spraying from. The thermo housing is the tall black thing sitting at the front of the engine with hoses running into it. The housing cap is flat and round with a slot for a 10mm Allen wrench. You can also check around the base of the housing with the engine off and see if there is coolant in the depressions right next to it. If so, you have probably found your problem. Mine started spewing with no warning.

If that is what your problem is, I can give you a complete parts list for the job, plus a couple of tools you will need. You will probably want to replace the housing, thermostat and all the associated gaskets and caps, as well as the coolant rail. All the parts for the job cost me about $175 from Motorcars, Ltd. (http://www.motorcarsltd.com). The job took me about an hour to complete and after having done one and having all the tools on hand I could probably cut 15-20 minutes off that now. It's not a hard job (the dealer wanted a grand for this job).

 

Orca, his car is supercharged and is configured quite a bit differently.

Gavin, your car is not user-friendly when it comes to repairs. Your time will be better invested if spent looking for recommendations from Jaguar owners in your area who have a trusted mechanic.

 

Sorry about that...

 

well i just had an issue with my 98 xjr and it turned out to be the pump. Mine would over heat and sometimes the overflow tank at the front of the engine on the driver side would spill out. Not too much tho, good luck man.