Overheating 1995 E220

When running hot, does the aux fan come on? Have you been good about the type of water and coolant used in your radiator? Open the cap on the top of the radiator, when cold, and look at the tubes inside--any white deposits? Now with the cap off, start it up and when it's hot see how well the water flows. If it's an anemic flow rate, could be the thermostat.

Thanks for the reply John. No I haven't been particularly careful about the coolant. Have done regular agency services though. Regarding the auxiliary fan. This remains something of a mystery to me. My reading (Haynes manual) has lead me to believe that the auxiliary fan comes on when the temperature of THE AIR behind the radiator passes some given temperature. The operation of mine follows this rule as when I stop. for example to open my driveway gate, the auxiliary fan almost always goes on but when the car is travelling along (and overheating) it doesn't. I'm sure the operation is entirely logical but I've never really undrstood why it wouldn't come on under a straightforward overheating scenario. Presumeably white deposits indicate less than optimal flow? regards

The gas engines typically run warmer under the conditions that you describe - no harm so long as the temp. is below the dreaded red zone. Diesels typically never exceed 80 degrees C except when climbing long hills.

Radiator cleaning is required when the engine runs hot at speed - lots of air flow so that excludes the fans leaving only the thermostat or radiator to blame.

Usually the fan temp sensor is in the coolant. But your fan is working so I'd check to see about radiator deposits restricting flow. Radiator shops can do a flow test but that's a last resort for me. Your eyes can tell you what you need to know.

Sounds like a fan clutch to me...? Those things only do anything when putting around town. Low airflow and little fan assist... my best guess.

-Mike