I'm not a tech, but here is what I would look at if it were happening to me.

1. Flush coolant and replace with original mb coolant at the correct water to coolant ratio.

2. Check thermostat for proper operation.

3. check for bad hoses.

4. check radiator water filler cap and replace if necessary.

5. check for proper operation of the water pump

6. check that fan and fan clutch are operatng properly.

7. check for worn or slipping belt.

I wouldn't do it necessarily in the order I listed.

I would start with checking everything, then flushing, then checking more mechanical items like cap, thermostat, pump, etc.

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U