Hello -

I have 1995 S500 with 106,000 miles. Just recently I noticed that the engine was running hotter than normal. Specifically, the temperature gage would rise up to 100C and even past 100C. This is without the AC running. Also the temperature would not go down rapidly even at highway speeds at an ambient temperature of 60F. In the past high rpm driving would reduce coolant temperatures. As a point of reference the engine used to run normally between the 80C and 100C mark only surpassing the 100C on the hottest days with the AC on. As a first guess I changed the thermostat with a new MB thermostat. Unfortunately, there was no change in the operating characteristics. It still runs hot even with a new MB thermostat.

Here are some more facts which I hope will help shed some light:

Water pump is not leaking (Water pump is original)
Radiator cap is original
Coolant level is good
Heater works fine
Coolant mixture is good with proper MB coolant
MB Thermostat is new and working
There is no evidence of coolant in the oil
There is no evidence of oil in the coolant
Engine runs fine overall

Last question - I assume a water pump is only bad if it is leaking through the weep hole to the outside, correct?

Thank you in advance for your help.

Regards.

Hynek

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1995 S500
1967 396 Chevelle
1963 Ford Falcon
1989 K5 Blazer
2000 Ford Ranger