Does my C230K need a new water pump and/or thermostat?
 

I have a 1999 C230K with 200,000 km (120,000 miles). It has the 2.3 litre supercharged 4 cylinder M111 engine. Runs well with great fuel economy.

This winter, in recent cold temperatures (-5 C or about 23-25 F) the car does not warm up to full operating temp of 90C - more like 70C to 80C. The air from the heater is warm enough but not really hot. When the car is idling the heater air cools noticeably and then warms as revs increase.

Is this normal? This doesn't happen with our other vehicles so I don't know if this is normal for this model or the pump/thermostat needs attention.

Also, the car has a difficult time keeping the side windows clear of condensation. I don't see any fluid loss at the water pump or loss in the amount of coolant.

Are these signs of a worn water pump or faulty thermostat? Anything else I should check?

Thanks,

Paul

Step one: Check coolant level and mixture. If that checks out proceed to step two.

Step two: Replace thermostat.

If the pump were going out you'd most likely be seeing overheating and/or leakage from the pump.

Thermostat
 

X2.

Out of curiosity, what antifreeze are you using in those frigid temps?

X3 Tstat

M111 thermostat
 

Thank you. Dealer has the thermostat (and very competitively priced). Will also flush cooling system as the existing coolant (Mercedes coolant) is 3 years old.

Thanks for your help!

Paul