Cadillac Repair/overheating


1990 Eldorado radiator fan not working. Changed motor & cooling fan relays. Both motors come on when heater/airconditioner turned on though. Stumped!

Hello Larry,

Your problem is so common to the Cadillac aluminum engines introduced in 1982. You may be dealing with a lost cause. This engine cannot be driven over 220 degrees or with the hot light on. If not shut off immediately the engine is literally melting!

By design, the engine does not need to be running for the fans to operate. If the ignition is in the ON position and a/c or defrost is turned on, fans come on.
The fans are not needed for highway driving ad only city driving when huge volumes of air are put through the radiator when driving on highway.

At this point, you need to perform  pressure test of the radiator cap which should hold at 15 pounds. The cooling system must be checked for any types of leaks. The common result of overheating this engine is blown head gaskets or a cracked engine block. If the tester does not hold pressure, you need to find the leak. Start with the tester applied at the heads down looking for external leaks. Check the oil dipstick and make sure it is not milky white. If so, there is an internal coolant leak in the engine.

If all good, have the engine warm up. Feel the top and lower radiator hoses for consistent warmth between the two. Place your hand on the radiator in all 4 corners and in the middle. Heats should be consistent. If not, there is a circulation issue that may be in the engine or the radiator.

These engines have very small water jackets and are plugged easily. If a water pump is replaced and a mere small piece of old gasket is left in the engine, that will plug the cooling system.

I suspect a circulation issue and if the coolant sensor does not see coolant, the fans will not turn on. If there are n leaks and heating to the hoses and radiator is consistent, you may want to have the system professionally flushed in hope that whatever is stuck in the water jacket or radiator will be dislodged.

As stated, something as minor as a radiator cap not holding pressure could be your problem.

These engines are not available in the junk yard because they have all been over heated. A GM crate engine was about $4k. You now have what is known as Pandora's box.
I hope my information will assist you.

Good luck!  

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Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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