My '94 E220 is a bit noise until it reaches full temperature. It's some kind of hard rattle that disappears when either the RPM is brought over 2000 RPM or the engine reaches normal temperature.

I was starting to believe that something was wrong with the camshaft bearings or some lifter machanism until I used the stetoscope. The noise most certainly seems to origin from the thermostat.

The thermostat is only 6 months old. When opened, it seems OK. Nothing loose and the spring is also OK.

Could it be the thermostat and what should I do with it?

Rgds,
Gunnar Woldmo