Latelly I noticed that after I shut off the car the fans keep on running for 5 minutes on my 2006 xj8. This is a car my GF drives and women dont always look at the gauges.

It didn't seem right so today I hooked up my scanner and went for a ride.

With 68* outside, when driving the scanner shows about 215*. When I stop for a few minutes the temp goes up to 245* and the needle keeps climbing towards red. What is strange thou is that when I'm parked and the car seems like it will overheat, the needle will drop down and the temp will drop to 220-225 but only if I rev the car up past 2500 rpm for several seconds. Is this a sticky thermostat? Did these cars suffer from the plastic water pump impeller issue?

The car has 58,000 miles.

 

Run, do not walk, and replace the thermostat and housing. assy. The plastic housing may have internal leaks and the thermostats can intermittently stick. All told, it is about $100 in parts. Do not keep cyclng to 245...it is destructive.

Even in the unlikely case this is not the root cause problem, it is necessary preventative maintenance on these cars.

 

This is EXACTLY what my 04 XJR was doing, and yes it was the thermostat. I paid $12 for the thermostat from Oreilly Auto Parts, and it is German made.
As I have the XJR, I have a cast aluminum housing, so I didn't have to replace that. Very easy job.

 

Took it apart today.





What a POS desing

 

Just FYI--I had similar issues and had a failed tstat housing. Replaced that, everything was good. Then later on had the dealer do a PCM flash for light throttle pinging. Well, after months of going nuts trying to find out why my fan started to run after shutdown, it turns out that this PCM flash will run the fan on slow speed in warm weather (looks at fuel temp sensor) to solve a fuel percolation issue. I never had engine coolant temps over 205 F, so it was baffling as to why my fan was running.

The Jag tech I spoke with said it's better to leave it with the new software and not have the hot start issues, even though I'm annoyed whenever the fan runs (mostly in summer temps only).

 

When you replaced it did you dig into the system to make sure none of the broken pieces were restricting flow?

I reached where I could and pulled out a few pieces of plastic from the block where there is a passage to the water pump. If somethig was restricting flow to the sensor that would explain the goofy fans.