Noticing fans running pretty hard after turning off motor. Normal driving 80+ degree temp doesn't happen all the time.


sensor not telling fans to run right speed or sticking thermostat?

 

I had the same thing happen last summer & it wound up being a water pump & coolant temp sensor.

 

So was the coolant tank full?

 

What flavor, XK or XKR? XK's have fiberglass reinforced plastic housings, the XKR and aluminum one. The T-stat is not self contained on these cars. The plunger pushes against the housing to open the T-stat. The housing fail and the T-stat doesn't open correctly. Engine overheats.

 

I'd put an IR thermometer on the hoses next time it happens to confirm the fans should be running hard, then if they should...what Ranchero said.

But I'd also put an IR thermometer on the hoses as the thermostat approaches it's opening temp and confirm it's not stuck open or shut.

Should start opening @ 192.5 F if memory serves.

It would also be helpful if you put the model and year in your signature.

 

Had the same thing going on with my 08xk. The thermostat housing is plastic and will crack up and break internally due to thermal material breakdown around 40-50k miles. If your car is a 4.2xk then I'd bet you need to replace that (along with the thermostat, its avail as a full assy). The part isn't expensive (IIRC ~$150US) but it's a bitch to get to and replace. I gave up after a few hours and took it to my jag shop but other more handy members here have done it themselves.

 

I changed mine out late 2015

Initially I just purchased the thermostat however once I starting pulling the car apart I realised the whole thermostat housing was also needed

If memory serves me correctly the temp sender is also part of the housing

 

08 XK 4.2
Yes tank is full
No smell of antifreeze
Shop says thermostat easy job
I'm leaning to sensor issue but we'll see.
Interesting that Tstat pushes against housing to open.

 

You could read OBD live data and see what the car thinks (i.e. is being told by the sensor) is happening. Cheap and easy plus can rule in/out various things.

 

Yes, absolute **** design. They did the same thing in the Lincoln LS and I went through two sets before tossing the factory setup and installing a '60's Ford thermostat out of a spare 390 intake I had in the shed. Had to cut it to fit but once installed the fan running at high speed condition that car had since I bought it used a couple years before went away. Terrible design.

 

I have a new tstat and housing I bought from the Jag dealership here in Plano if you want a good deal on it. I bought the housing and stat and replaced them but then had to replace the other part of the setup and had to buy the whole piece which included the tstat and housing again. Will sell them to you for a good deal if you need them.

 

Thanks for the offer.
So here's the deal.
Inside the thermostat housing there's two stubs which hold the thermostat cap (crown) in place. This allow the thermostat to push against it to open. Both of these tabs broke off allowing the thermostat to sit in there cockeye. On cool days it was enough to keep the engine cool and the fans ran normal, but on warm days the fans ran excessive after shutting down
The shop took 1 hour to replace thermostat fixture.
Cost labor $100
Thermostat housing assembly which is quite a complex molded piece with sensor $169 from Jag but only needed T housing so still have the rest of assembly.
1 gallon of orange antifreeze $24
Total $320
Told common problem with 4.2L motors.

 

Yep, good deal that it wasn't terrible. Hopefully those broken tabs were accounted for and won't get in a fight with the plastic water pump impeller.

 

Ended up changing out water pump since some of the impellers were damaged.

 

How did you know the engine coolant pump was damaged?

I replaced the thermostat and thermostat housing on my 2007 XK (78K miles) this past weekend. One tab on the housing had broken off and that piece was sitting in the outlet tube so I could pluck it out.

I'm just wondering whether further work is needed on my car.
Thanks!

 

These cars are now coming up on 8-10 years old, the thermostats are due for replacement. I think we will see a lot more posts on this subject as time goes by.

I replaced the thermostat in my XJR at 10 years old, it the original one and it was stuffed, dropped it into a glass of boiling water and it didn't even open a fraction of an inch. Dropped the brand new replacement in and it sprung open.

Thermostats don't last forever, in the "good old days" we used to replace them every couple of years, seems like that has been forgotten with modern cars...

 

Even after changing the T stat and water pump still have an overheating issue when at idle. As long as the car is moving no issues but stop in traffic and the alarms start.

 

Without having a temp gauge how have you determined you have an overheating problem. If you can monitor your temp. what is it. It should run between 195*F -210*F. This would be normal. As for the fans turning on I don't have that range but I suspect it would be over 210*F. With a new thermostat and WP if you continue to have temps higher then normal it sounds like you may have a blocked radiator or some deteriorating hoses.

 

Have you changed the "pipe-outlet" yet, which is the complex black plastic assembly that the thermostat fits into? If not, maybe the engine coolant temperature sensor is reporting higher temperatures than correct. You have to remove the pipe-outlet for access to the sensor so you'd might as well replace the whole unit at once.

You might also use an instant-read IR thermometer to see what is the temperature of the radiator hose on the right side (passenger side in LHD models) of the pipe-outlet, and compare to the temperature of the radiator hose on the left side which is the cool side coming back from the radiator.

On hot days with 95 degrees F ambient air temp, I am measuring around 185 degrees F on the hot side and 155 degrees F on the return side, so I am assuming the system is working OK even though the radiator fans run for several minutes after the engine is turned off. At least they are not running as fast as they used to when the original failed thermostat was still installed.

I changed the pipe-outlet this past weekend on my 2007 XK and it wasn't that bad. You just have to remove the engine air intake duct and throttle body for access. This gave me an opportunity to clean the throttle body interior and throttle plate.