Ford Focus Forum, Ford Focus ST Forum - View Single Post - Changed almost everything but car still over heats!
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Old 07-09-2012, 03:44 PM   #4
sailor
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Sounds like the "normal" readings you'd see if the high speed fan circuit is working, and the low speed is not.

As the engine warms up, the thermostat opens enough to maintain temperature at the correct point - as long as the car is moving & the outside temp is reasonable this gives all the cooling needed & the gauge stays near the bottom of the "normal" range.

When it's warmer out, or the car isn't moving enough for air flow through the radiator, the "low speed" fan circuit kicks in - cooling the radiator 7 hence the coolant so the thermostat can do it's job (it's full open at this point) and the needle can go near the high mark on the gauge when this is happening.

High speed fan operation (when needed) usually doesn't kick in until the gauge is at or near the red zone, and if the low speed circuit isn't working temps will "spike" into the red zone B4 the high speed fan operation can "catch" the rapid heating & bring the temp back down....

You didn't happen to mention HOW you checked the low speed fan operation, OR whether this is a new symptom from a car you've owned - OR a worrisome gauge reading on a newly purchased vehicle.

High & low run off separate relays, so if you AREN'T getting low speed operation that might be another area to check...

Luck!
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