At 100,000 miles my 1998 XJ8 has developed a pronounced tap in the engine at startup, whether cold or hot. I can't hear it from inside the car, but after driving a few miles if I pull over and listen it's gone.I had the timing chain and all tensioners replaced around 65,000 miles. This latest noise sounds just like a bad hydraulic lifter. Do these engines do that?
Any advice welcomed.
The noise might be the Variable Valve Timing units [VVT]. One way to prove it is to open your bonnet and start the engine WITHOUT TOUCHING THE THROTTLE. Listen for the noise and let the engine settle down from the initial high idle. Once you are certain the noise is present, goose the throttle quickly ONCE, about half way down. Doing that forces the VVT's to be exercised and charged with oil. If the noise shuts up right then, they are the source of the sound. If that's it, that means taking the front of the engine down again to replace them.
If that doesn't narrow it down, a little more detective work is in order. Let us know if that helps.
Thanks Steven. As it happened, I took the car in for100,000 mile service and the Jaguar serviceman agrees it is the VVTs. I'd had them replaced about 35k miles ago, at the same time as the timing chain and tensioners. The Jag guy suggested I don't replace them - any thoughts on that?
Gee, I think that's a little unusual for them to be noisy again already, but I'm inclined to agree. Generally it's only on startup or a period of extended idling that the noise shows up. If it's not really objectionable, let 'em alone and just keep an eye on 'em.