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Cadillac Repair/1998 CADILLAC DEVILLE

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Question
COOLANT FAN IS NOT WORKING CAUSES THE TEMP TO GO UP VERY HIGH.  BUT IF I TURN ON THE DEFROST OR A/C BOTH FANS TURN ON WHICH CAUSES THE CAR TO COOL DOWN.

Answer
Hello,

Well, as you are driving this vehicle with an aluminum engine, components are melting and imminent irreversible damage is occurring. Shortly, the result of overheating this engine will be blown head gaskets, potentially a cracked head or engine block.
If this engine reaches 220 degrees or higher or hot light comes on, if not shut down immediately, its going to be the demise of the engine to the point there is no return!
You will not find a good junkyard engine either because a majority have suffered from the same problem.

The only answer and I don't even know if they are even available anymore is a GM crate engine at $4k+.

These engines are not like the old cast iron Chevy engine where over heating rarely created any damage.

Your fans come on with the A/C and defrost by design. The engine does not have to be running for the fans to come on in this event. Only the ignition hs to be on.
What you are doing is using a bandaid that may not be preventing destruction of the engine.

These engines were great for performance and mileage, but the Achilles's heel was overheating.
I have been answering questions on these engines since first introduced in 1982. Check the archives.

These engines had very small water jackets and it did not take much to cause no circulation in the cooling system. Many think all they need to do is change the thermostat. The problem in this engine has almost never been the thermostat. Let's say a water pump is replaced. Possibly gasket remains were left in the engine inadvertently. That is enough to plug the cooling system!

The radiator is plugged just as easily. Blades (impellor) break off the water pump in these engines. A faulty radiator cap not keeping pressure up will cause lack of circulation.
I know why your fans are not coming on as they are supposed to. The cooling system is not circulating for whatever reason and the coolant sensor is not seeing that the fans need to be turned on in city driving. On the highway air rushes through the radiator and the fans are not needed.

I hope you have not destroyed this engine. Have the system checked with a cooling system pressure tester. If it holds pressure and is not leaking coolant from the block, heads externally and internally, the engine can be saved.

Next, have the coolant system professionally back flushed. Once engine is warmed up after running, feel the radiator top, bottom and sides. Temperature should be consistent. If not, you have a plugged radiator.

Check the temperature of the upper and lower hoses. If everything is good, you may need a coolant sensor.

One has to realize GM possibly did not leave a warning in these vehicles about overheating so they could sell engine and they sold lots!

The Renault Alliance with their aluminum engines also were overheated commonly and the pistons would melt. The difference was that they were much more inexpensive to repair because one could change the piston liner kit. Cadillac required an engine.

You could have Pandora's box here. You are not going to get away with running the A/C and the fans very long before the engine suffers substantial damage.

Good luck!

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Rob Painter

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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?

Experience

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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