I have been trying to track down a heating problem on my 190E 16v. I have noticed that after the car has heated up, if I turn the heat on full blast I get warm air out of the vents but then it gradually turns cold. I am pretty sure the heater valve is ok, I am suspecting the auxiliary water pump. What do you think?

It definitely sounds like a lack of coolant flow. I agree it could be a valve or pump.

There is a small, outside chance of a plugged heater core if the coolant wasn't changed at reasonable intervals, or ever, and corrosion build up is clogging the core.

Can you bypass the valve temporarily? If so, and the problem continues, the probably the pump isn't pumping.

Can you apply power to the pump and check for running?

BCingU, Jim

I have the same heat fading problem with my 190E. Did you solve your problem? What was issue? How did you solve it? Did you test the Auxiliary water pump?

Thanks,

Chris