I suspect my problem may be something as simple as a weak cooling system pressure cap(cap on overflow tank).

'91 300-SEL equipped with MB pressure cap 124-500-04-06. Cap is about 2 yrs. old.

At highway speed, temp. gauge reads normal - about 87 degrees centigrade. In stop-n-go, it runs between 90-100C.
Running temps are no different than they've ever been.

After coming to a stop and shutting off engine, I hear all sorts of gurgitation under the hood. Coolant is overflowing rapidly into the expansion tank. I'm seeing some come out from around the cap. It also appears that there may be some seeping out along the seams of the tank.

If it were the T-stat, I would expect to see high temps while driving. - this doesn't happen.

This situation came on out of the blue. Thanks for your time.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"