Thread: I think I just found my overheating problem .........

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Above about 20mph a running fan actually restricts air flow by "getting in the way" of the air being pushed through the radiator by the vehicle speed. Your electric fan will freewheel in the air stream, much like a mechanical fan with a thermostatic clutch does. For a coolant thermostat of 180F SPAL tells you to put your "fan on" setpoint at around 185 to 190, and your "max speed" setpoint at around 205 to 210 (15 to 20 degree delta). The fan only runs when idling hot, or when stuck in traffic at no/low speeds. A toggle switch works just fine as long as you remember to keep an eye on your temp when you're angry about the traffic jam you're stuck in. And yes, you pay for running the electric fan in lost efficiency of the engine cranking the alternator - the higher your amp draw the harder it is to turn, using HP that would otherwise be going to the rear wheels - nothing's free. The only reason I use the electric fan is clearance issues - not enough room for the fan/clutch off the water pump pulley.