I was smelling some hot coolant and could not find it. Looked today when cold and found orange residue in tstat cap. It was full to top and I cleaned most of it out. I'll have to watch this carefully.

 

It's probably time to replace the housing. The aluminum after market type is the preferred choice.

 

+1 on the Aluminum housing. I replaced mine last year with one from Welsh. One less thing to worry about. There are several write ups on how to get the back two bolts out.

 

Sure wish I had an aluminum option on my wife's 2006 4.2 engine. Had to replace the plastic coolant outlet duct / thermostat assembly just over a month ago. No aluminum alternative available, so I installed a new plastic one. Disappointing....

 

Don't watch carefully, REPLACE IT. These motors don't like getting over heated if you end up WATCHING it sitting along side the road. EASY REPAIR, fix it now.

 

It seems peculiar for a leak there. I wonder if I have a leak that shoots fluid over the cap.

I replaced this with an aluminum version on my other XK8 years ago. The quality of the AL part was poor. Who is making the best quality one or is there a single maker and it just gets rebranded?

 

Welsh Enterprises sells one that many forum members have used with good results. They often have a good price that includes the thermostat.

 

I wish these were avail for 03 and up.

 

That 10mm Allen wrench socket at the top is inviting but anyone that uses it to remove the cap is guaranteed to create a leak there. The cap should be removed with a strap wrench.