Or is it only a 4.0 problem. I found replacement kits for early cars on-line but nothing offered for later cars (mine a 2004 XK8).

Ken

 

Yes they do fail, but there is no metal replacement.

 

Be sure to replace the entire black plastic assembly, not just the thermostat housing. That black plastic tends to get brittle and warp as the years and drive cycles go by. Jaguar calls that assembly the coolant outlet duct. There are a number of descriptive threads here on the forum that will ensure you do this job right. Remove the metal front manifold plate to gain access to the two rear bolts on the coolant outlet duct that give everyone so much trouble. Be sure to also buy the replacement gasket that goes behind the metal plate before you do the job. That gasket will be cooked from the heat cycles so you'll want to replace it to ensure no air leaks once the plate goes back on....

Good luck....

 

There is no metal T stat assembly for the 2003 and up models. Sure they are plastic but mine made it to 98k miles. I am good with that life span for the part. They don't make cars like they used to where that crap lasted for 25 years. Just how it is now days. made to fail.