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Cadillac Repair/1986 Sedan Deville Coolant fan light comes on intermittently

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Expert: - 7/9/2011


Question
I had a water pump put on a few months ago and the person put it on wrong. I have to put antifreeze in everyday and today I noticed a hesitation and then the coolant fan light came on. Can you help me figure this out and what does it mean when the service soon light come on. The car has about 102,000 miles on it and runs good for the most part.

Answer
Hello,

Service engine soon tells you there is a diagnostic code set off in your computer. I no longer have the codes for these cars or even remember how to obtain them. It did not require special equipment in a car that old. As I said, it been too long to remember. The coolant fan light may relate to that.

Here is what I can tell you. If you have a leak (and you do not ever run one of these aluminum engines hot because you will destroy it instantly), you are lacking cooling system pressure. For the coolant/antifreeze to circulate, you are required to have 15 pounds of pressure. When the cooling system is not circulating properly, the cooling fans will not work properly, and the engine will potentially over heat in city driving situations.
Fix the water pump, you coolant sensor will work properly and your fans will work properly.
Do not put stop leak in this engine either because it is known to cover the coolant sensor in the engine that controls the fans.
See, there is a sensor in the engine that determines the engine temperature and when the fans can come on.

These water pumps are not hard to install and I don't know what the guy could have done wrong short of breaking a bolt or not getting all the old gasket off.

When you do change/repair whatever, make darn sure there is no old gasket falling into the engine because something as minor as leaving old gasket material in this particular finely engineered (sarcastic) 4.1 aluminum engine is a major problem.

I am pretty sure once you get your leak fixed, your fan problem will go away and you can have the computer reset and the service engine soon light will go out for good. At least for that issue. In other words, all your symptoms are related.

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?

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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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