I have a 91 350 SDL 175,000 mi that I have had for 2 yrs with few problems. The car seems to run hot now if the AC is off. I understand that that could be the fan clutch not engaging at 100c or the fan clutch switch. I have purchased a new switch but cannot find where it goes (do I want to have a mechanic do it or can a do-it-yourselfer handle it)...Am I on the right track? Please help...thanks

If it is running warm without the fan on, I would have to assume it is bacause of the lack of the auxillary fan. Therefore, I would think that the thermostat, or fan, or radiator could be at fault. Without the a/c fan on, the engine should not need the help of the auxillary fans to keep cool.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

The car only runs hot when it is over 80 degrees out with high humidity. If I drive on the highway, it cools down, if I drive with AC on it cools down. I explained the problem to a tech and he suggested that there is a switch that went bad (which I have an new one of and have not replaced yet). The part is a Cylinder that has a 1/2" screw in post on one side and 3 contacts on the other. Should I replace this? Is this something that I can do myself, or should I have it done? Where does it go? THANKS FOR YOUR HELP I APPRECIATE IT.

Had the same problem with mine. For $50 I had the radiator flushed and the problem disappeared.

I beleive if you can check the fan itself by unplugging the sensor on the block the fan will run constantly.

Your fan clutch isn't electric. It's got fluid in it.

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1991 350 SDL
114,000 miles