I drive a 99' E320 and Recently i've been driving around and i noticed that the temperature of the car rises to the 100 mark and just keeps getting higher very gradually, i have checked my coolant fluid and check for leaks in my radiator, and those where fine but then i noticed that the engine fan doesn't kick on. so i resorted to checking if the fuses where okay and they where, so now I'm left clueless i had no luck on finding an answer on this question. Was wondering if anyone had any ideas on what could be wrong? thanks

 

Welcome to the forum -

First, I am assuming you or anyone else hasn't added any water. If so, as you dilute out the 50:50 ratio you lose a little cooling efficiency. Also, no additives have been added to the coolant system?

1) Most common cause of overheating is fouling of the radiator with corrosion products. If you replace the coolant every three years with the correct ratio of MB antifreeze and the old coolant looks the same as the new coolant, that should not be the problem. Although, radiators like other automotive parts don't last forever.

2) Examine the coolant for contamination. Either oil or automatic transmission fluid. Oil fouls the heat exchange surfaces and greatly reduces the radiator's efficiency.

3) Your thermostat could be failing. Failure to open all the way will result in a hotter running engine.

4) The coolant temperature gauge on the instrument panel could be failing. Run the onboard diagnostics in the CC unit and compare.

5) For the fans - confirm that they actually come on. A fuse check only means that have a voltage supply available. Also, always check fuses with a DMM or continuity checker as they don't always look 'blown'.

 

Thanks RichardM98
i've checked the fluids in my return tank and the fluid is very clean and show no oil or contaminants. so now im gonna check the thermostats, and get that replaced. and probably get the temp sensor checked out. Thanks again.