Overheating XJR

[BigD]

Hi All,

Any light you can throw on the below or any advice you can offer would be greatly appreciated.

My 2006 XJR is driven from London to Ayrshire, West Coast of Scotland without any problems. Car is MoT'd, a clean bill of health in that respect.
10 minutes after leaving the MoT station to take the car for a service the temperature gauge shoots up into the red. I pull over and switch off the engine. Checking under the bonnet all seems to be ok, no hissing or clouds of steam. I get back in the car after 5 mins and the temp gauge is back to normal so I try to continue. 5 mins later the same issue. As it's raining like hell I call the RAC and have the car trailered to my local Jag specialist around midday. I call them at 4:30 pm and they say they have been running the car all afternoon and can't get it to overheat!! Service is done the next morning and the car tested again by them, again no overheating, so I pick up the car late afternoon.
I have the car 10 mins and the previous morning's issue returns, I'm getting a bit paranoid now, so straight back to the specialist. This time coolant appears to be being forced out of the expansion tank pressure cap over the top of the engine. A replacement pressure cap is fitted, the coolant topped up, engine run for a while and all seems ok. It runs ok for the rest of the day. The following day I drive on the motorway for around 5 hrs then the problem returns, fortunately close to a service station, so I pull in and inspect the car. Same problem with the coolant appearing to be forced out of the pressure cap. So I gently release the cap, top up the fluid and wait for 20 mins. Temp gauge is now normal so I gingerly set off, being prepared at any moment to have to call the RAC once again. I drive 3 hrs with no problem then 200m from the end of the journey it happens again.

Apologies for the ramble but I wanted to try to convey all the events. Any ideas??

Many thanks,
Dave

[BrianG]

Hi Dave,
Your problem sounds very much like the one I had with a Rover SD1 V8 EFi I had some years ago. On the SD1 the pressure cap can vent into a catch tank and syphon it back when cooling. My car would periodically show high temperature on the gauge for a few minutes and then cool down to normal, regardless of driving style at the time. Performance seemed normal during this event but on viewing the catch tank after such an event this had clearly overflowed through its dump hose onto the floor, so as a bodge I then added a second catch tank (old plastic bottle) on the end of the dump hose so that the coolant was not repeatedly lost. This still left the problem of the occasional temperature gauge high reading. I eventually found that there was corrosion creepage under one head gasket that would pressurise the system seemingly at random. This was not to be found with the usual tests for a head gasket fault.

[J44EAG]

I have several posts in the Engine.coolant sections on S-type and X350(R) on this site on similar issues. In addition my cases on both cars were reported in recent magazine pages.

As the car is an R, turn the ignition key to position 1. Squat down at bumper level below the OS main beam head light. Listen for the tell tale sound of the intercooler electric pump running. It should operate at all times once the key is in position 1. If not operating check the fuse which I recall is F27 or 32 in the underbonnet fuse box. If the fuse is intact, the Hella make circulation pump may have failed. If it has, replace with the cheaper and higher flow Bosch unit available via ebay for AVT Tuneing in Essex.

You should also look towards replacing the thermostat which is a unit known to become troublesome from about 80k miles. A duff stat causes similar issues to the ones you describe. Note there are several different stats fitted to the 350R dependent on model year. You might also look to replacing the cylinder head temperature sensor as it is also a unit which can fail at 80k miles. I`ve done two now at those mileages. Use only genuine OE Jaguar parts for this critical location.

Mike K

[BigD]

Brian, Mike,

Many thanks indeed, that gives me a number of things to go on. I had fears of a head gasket problem but let's see!!
Cheers,
Dave