Hello -

I have a 1995 S500 with 53k miles. The car runs excellent, however, I have a few questions with respect to "normal" operating temperature. The conditions I notice are as follows:

1) During prolonged idling in traffic coolant temp approaches 100C at ambient temp of 50F.(The electric fans do not turn on as I assume the engine is not hot enough)

2)While driving (moving) the coolant temp is stable just above the 80C mark.

I am new to the S-Class and do not remember my prior 300E reaching 100C at such a low ambient temperature. I know that the thermostat is 80C which tells me that at anything above 80C means that the full cooling capacity is being used due to the fact that the thermostat is allowing full unimpeded coolant flow. Also, I expected that since the engine is all Aluminum (higher heat conductivity)the engine would run cooler not to mention the high oil capacity. Needless to say I am confused:

Should I be nervous idling in traffic and believe my thermostat is sticking or are these observations normal?

Any response would be appreciated since I have not even reached the 90F days with the AC on in traffic.

Hopefully I will soon be able to sleep better and not think that I am a heartbeat away from burning up a Mercedes 5 liter engine.

Thank you in advance -

Hynek