2003 XJ8 X308 engine donor car options

I have a 2003 XJ8 with 150,000 miles on it. It is a wonderful car and runs very well but the engine sounds rather rattley up top (Oil changed every 5K miles with Mobile1) I would like to either install a low mileage engine in it or rebuild the current engine. Can anyone make any suggestions as to which way to go here? I have a transmission question as well but will post it separately.

Are you certain that your timing chains and tensioners are OK?

While your 2003 should have improved chain tensioners, I’m not sure if those were the final, reliable design. If the tensioners are going bad and you keep driving it, you’ll be looking for the replacement engine most likely (or at least a top-end rebuild.)

Like any engine, diagnose the problem first. It could be just worn (as opposed to failing/defective) timing chains. Those could be replaced for maybe $1,000 if you farm out the work to a dealer, less for an independent, half that if you do it yourself.

Check the compression and leakdown of the cylinders, trying to isolate if it’s the bottom end, the top end, both, or neither that need work. Perhaps just the valve guides and/or seats are worn and it needs only the heads rebuilt. That wouldn’t be as expensive as a full rebuild. Is it burning oil? Lots of things to check on. Good luck.


Hi Dave,
Thanks for your reply. The engine in mine is the AJ26 and is original, which I believe means it has the updated timing tensioner.
I will look into the other things you mentioned.
Thanks again,

I’m going to go ahead and replace the tensioners. I’m seeing tensioners available everywhere online. Is there one brand that is best?

Your engine is AJ27. AJ26 was installed in the X100 and X308 up to 1998 Normally Aspirated and up to 1999 in the SC X308.

From engine engine SN 0108130000 onward the timing components were upgraded to the Morse style silent running with metal body tensioners.

Basically any 4.0 AJ27 from 2000 to 2003 (1999 NA) will work in you car (X100 or X308)
Engines prior to engine SN 0108130000 will need to have the timing components checked and/or replaced.

Thanks for that information! What year did engine #0108130000 come out?


00=zero minutes

Now THATS service! Thank you sir!!!