1990 190E 2.6 When driving up hill for a half mile or more the heater comes on - not the fan. It does not matter what the temp dial is set on the heater comes on to the max. If the A/C is on, the center vents blow cool air while the side vents blow hot air. A dealer has looked at this on a couple occasions and has not been able to find anything to cause it. Once the load is off the engine, the temp returns to normal in 20-30 seconds.
Well that means the auxilary coolant pump is comming on somehow. I am assuming the engi...
Well that means the auxilary coolant pump is comming on somehow. I am assuming the engine is at a higher RPM than normal crusing speed. That is a very odd problem. Might want to check out your alternator and voltage regulator.
Plus side to your problem is that when you drive up a hill you won't have to worry about overheating! :) heh heh