Hey everybody, I have a pretty substantial coolant leak coming from the thermostat cap on my 2001 XJ8. I upgraded the thermostat a few years ago to the new metal one. I filled my coolant resovoir up this morning and within 5 min of driving I was getting low coolant messages. Looked around and it is definitely the metal thermostat cap. Can this cap be removed? O-rings failed? Any help would be greatly appreciated.

 

Replace that metal cap with a OEM plastic one. I know it seems like a downgrade but, they at least seal. It's kinda cool looking for a removable part but, I think it should be welded closed after the seal is removed if you ask me.

 

I had a problem with one right out of the box. The o_ring wouldn't seal. I took a piece of solid rubber and cut a disc and used it to replace the o-ring. No more leaks.