Mercedes: 300sl overheating, radiator shop, radiator cap

Question
I have a 1992 300sl that is overheating, I have replaced the radiator cap, upper and lower hoses, thermostat, fan bearing (it was shot), and had it pressure tested. I still hits into the red zone. What should my next checks be?

Answer
Brian,
I would have the radiator flushed with a chemical flush. Mercedes dealer may be able to recommend an DIY product. It may require removal of the radiator and service by a radiator shop.  With age the coolant causes gum in the system. The veins in modern radiators must be very clean to allow proper circulation.
You did not say what outside air temperatures you have. The coolant must be the right mixture to allow the system to rise in temperature without boiling over.  All engine cooling shrouds should be in place too.


Also Oil type and quantity will affect heat retention.

I would change to a 0 W 30. or 10 W 30 if the 'O' is not available. Also new filter.
As oil ages it gets thicker and that can effect engine cooling and performance.

The final remote possibility is leaking head gasket, but you would be loosing some coolant and moisture in the tail pipe or milky oil if that is the case.

Good Luck
Rob