At about freezing, I get a knock from the serpentine belt tensioner on my 2000 XJR. It only lasts 20 seconds or so. I can see the tensioner move 1/2" or so, snap back (KNOCK!) and repeat.

My guess is that one of the accessories is tough to turn when cold and I'm seeing the belt tension go up and down until it settles out. Other thoughts are a stretched belt allowing the tensioner to reach a limit it wouldnt see otherwise or a problem with the tensioner itself. the belt never squeals BTW.

Thoughts? I have a new belt to go in when I find the time for the SC coupler but if there are any other parts I should be checking, I can plan to replace them too.

 

I'm gonna subscribe to your post Finnell, as the tensioner on my daughter's car is doing the same thing. I can't see that the belt is slipping to sticking and the only sound I hear, is what I believe to be the tensioner knocking as it ratchets back and forth.

 

I gather this isn't an unusual problem but haven't heard any solutions yet. I haven't had an opportunity to look at my car yet though. Busy with garage upgrades.

 

There have been a couple cold weather belt tensioner threads in the past several days. At least one was resolved with a new belt.

 

It seems that we both have the same problem only mine is on a 99xk8. Shame on Tom not to tell you or me that!!!! Take a look at my post https://www.jaguarforums.com/forum/s...ad.php?t=29520 I replaced the belt for the second time the other day and still have the problem. I am going to replace the tensioner and idler tonight and see what takes place. I will let you know!