It uses a hydraulic tensioner. Looking at the MB manuals, Steves insight is interesting. It is very reliant on oil be pushed through it and there being pressure. I am very curious to see if my change to mobil one 10w-30 will affect it from thicker 20w50. On paper it looks like it could I think. I also wonder what affect sitting for days has on the chain sound versus overnight. It seems to only do it sometimes and lightly after sitting for days. A new tensioner wil arrive monday but i think I might wait and observe a bit more before I change it myself, still havent decided. It looks like an easy job but I have learned to not touch this car unless I have to. On the other hand, any chain sound at all is scary. The tensioner in there is 2 years old and has 6000 miles on it.