Issue: I have a 2001 E320 with 254k miles. Lately the engine has been overheating, normally the temperature sits around 80 degrees but it has been getting up to 95-97 at which point the engine shuts off and wont start again till the temperature drops back to 80.
Symptoms: While driving the freeway maintianing speeds 60+ mph, the temp will stay between 80-85. When in stop-and-go traffic the engine temp go up.
What I have checked:
The radiator fluid level is good, up to the full line.
The coolant return hose gets HOT to the touch.
The engine fan turns on when AC is on however it did not turn on when the engine temp reached 85-87. I'm not sure at which point it should turn itself on. I have not looked at the fan at higher temperatures.

 

Sounds like its time for a new thermostat !

 

As I noted, when maintaining high speeds the temperature stays down, when in stop-and-go traffic(low speeds) the engine temp goes up. To me this sounds like the air flow at the higher speeds through the radiator is helping keep the engine cool but wouldn't the engine fan produce the same effect at the lower speeds?

 

I just checked the fan after having the engine temp reach 95 and it was not on. Is there a fuse or relay for the radiator fan?