Cadillac Repair: 92 eldorado is overheating,straight wired the fan and works. what is wrong?, mileage engines, high mileage

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Answer
Hi Patrick, It would help me to know what engine you have but here's what might be happening.

         Not knowing where or how you wired the fan sounds like its safe to say the fan motor isn't the problem of the overheating. Maybe the fan fuse is blown. On older vehicles the fan relay contacts can get worn and not allow voltage across the contacts which requires the relay to be replaced. Temperature sensors can go out of range and tell the computor the engine is colder that it is and the fans won't turn on. If the anti freeze level is low then the sensor can't acurately tell the temp. Normally the fans should turn on at around 106 degrees C for the 4.9liter and 217 degrees F for the northstar. To get an accurate engine temperature sears makes an inexpensive infrared temp gun that you point at things and it will show the temp. That way you will know if the engine really is overheating or if a sensor is defective. If the car were in my shop a quick test would be to test the differant temp sensors the computor sees before starting the engine after sitting overnight and if one is say 3 degrees or more off than the others that one should be replaced and that could fix the "problem". What is happening with older high mileage engines is a head bold threads pull out of the engine block and that will cause overheating but the fans should still run.

        Let me know if I can be of anymore help. Bill