I just recently bought a 1985 Mercedes-Benz 190E 2.3 8V Grey Market with 105k on it. I had it for a week before I had a slight transmission issue where as I had to replace the transmission coolant lines and the transmission filter and gasket because previous owner wasn't very honest (previous vehicle was a 1991 Mazda Miata with 93 Eunos Roadster swap purchased from General David Petraeus, story for another time).

Anyways, I then had the same issue of my '85 Baby Benz slightly starting to reach past the 85 Celsius mark in traffic. So with the hood propped, I noticed that the main cooling fan (large 5 bladed yellowish fan) was running but not so fast as if I would put my hand in it, it would stop. So being unfamiliar with the Mercedes-Benz w201, I had a friend who knows more about them tell me it needs a fan clutch and water pump.

So I ordered aftermarket replacement parts $70 for water pump Autozone, $40 for electromagnetic fan clutch, $25 thermostat, $25 Mercedes Blue Coolant. and $100 to a local mobile mechanic (he told me $100 before looking how long it would take and boy was he pissed when he left 4 hours later).

So all parts installed, found that the factory Engine Cooling Fan Sensor that screws into the side of the water pump, didn't fit the new water pump that did happen to be an exact replacement for the factory one. So now I have to go buy a Engine Cooling Fan Sensor for $35. I guess its better than having blown motor.

My question is, does the Engine Cooling Fan Sensor that screws into the side of the water pump actuate the fant clutch to engage or is there another sensor that actuates it to engage? After installing all these brand new parts, the car ran better, but the main yellowish coloured fan didn't seem to spin at a solid (you don't want to put your hand in there) kind of pace.

My other car (1966 Ford Mustang Fastback with '03 SVT Cobra S/C swap has same issue with water pump, but when water pump replaced, car and fan were fine)