friendlystart

Hello, I am currently getting a rattling noise on cold startup my 2001 996 cab for about 2 seconds and after the engine warms up the noise goes away on startup. I suspect it is failing timing chain tensioner and plan to get the 3 external timing chain tensioners replaced. However, my mechanic shop is telling me that I should replace the 2 internal Vario cam tensioners too which is a big job. There is no check engine light an as I mentioned the noise goes away when the engine warms up which makes sense being the 3 external tensioners are hydraulically actuated. What are signs of the Vario cam tensioners failing? Quoted $1,700 to replace the 3 tensioners and $8,400 for replacing all 5 tensioners. Thanks

plpete84

A good way of verifying the chain tensioners is to check the cam deviations with something like Durametric. Also, when changing oil, drop your sump cover and look there as well as your filter for small plastic bits. That would serve as a good confirmation. These engines can also rattle at start up if not driven often and quite often it's the hydraulic lifters making noise until they fill with oil again. That noise should go away rather quickly or once you tap the gas pedal a bit.

SimJen

Mine does the same, car is often left a week or so between weekend drives and will do it most times. If i leave it a day or two between starts then it wont, which indicates to me the hydraulic chain tensioners that can slowly lose oil over a period as they get older. They still work fine though and shouldn't cause other issues. Some people replace these if it annoys them.
Starters can also cause a similar noise from dry bushes and pinions not returning. It could also be as simple as one of the exhausts heat shielding!

sublm8

New tensioners, new variocam pads, new cam chains:

my car still does this on cold start.

De Jeeper

Meh....start up a mezger motor after its been sitting for a week. It sounds like a box of rocks in a tumbler.