2004 US version XJ8 with 4.2. 49,000 miles, always perfectly maintained and always with Mobile 1. Loud noise only occurs at morning start up after sitting overnight. Noise does not repeat once started and restarted during the day. Sounds like tappets and only lasts a second but it is loud. Seems like lubricant is draining overnight and upon starting things are back to normal. Have been told tensioners but 2004 are not known for tensioner issues and the $3500 quote is a lot to swallow. And have been told by others that they have same problem, replaced tensioner but still have same noise. Had engine flush to clean out carbon buildup but no change. Post on another section of forum had same problem quite awhile ago but they never posted a final resolution.

 

The 3rd gen tensioners have a ratchet mechanism to maintain tension overnight that occasionally fails, according to some members. This would allow the chain to rattle on startup, and I expect it could allow the chain to skip a tooth.

Replacing the upper tensioners only will remove that risk. The quote for that is usually in the $600-$800 range, or as a DIY using the zip tie method less than $200 if you can reuse the valve cover gasket.

It is not difficult to remove the covers when the engine has not been started (overnight) and see if the tensioners have collapsed and the chain is slack.

 

But, he is on the wrong forum (X350 for the 4.2 mills).

 

Jim,
I get the impression he checked the X350 forum and didn't find an answer, then came here. This is the same engine used in the 4.2 XK8, isn't it?
Ron

 

NO, it isn't. X308s use the 4.0 liter variant.

Try the XK8 forum

 

No, Jim, I meant he has the same engine used in the 4.2 XK8. Anyway, suggesting he go to the XK8 forum is something I should have done, so thanks.