Hope this helps someone.


My car has been making this knocking noise when cold since I've bought it one year ago. The noise would go away when hot so my worst fear was that it was piston slap, but it just didn't have that metalic note to it that I've heard from other vehicles with piston slap. When I finaly used a stethoscope on the engine I traced the noise down to the tensioner shock on the fan belt assembly. After searching this forum I found a post where a member found that there was too much clearance between the bolt that mounts the tensioner and the eye of the tensioner. I checked mine and found the identical situation. He used Teflon tape wrapped around the bolt ot take up the slack but I tried a length of shrink tube over the bolt instead. Sure enough the noise is gone. It's hard to believe it could have made so much noise. I spent a year wondering if my motor needed a rebuild and in the end I fixed it in 10 minutes for free.

Jorg

I have something similar at cold startup.... I think I will take a look at this in the near future.. 1989 300e

What's shrink tube?

Shrink tube is typically used for wiring insulation.

It shrinks down snugly when you apply heat.

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2012 E350
2006 Callaway SC560