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Expert: - 8/15/2010


Question
My 1984 cadillac eldorado overheats only when A/C is on.  What may be causing this?  Thanks!

Answer
Hello,

There is not one standard answer here and there are many that have to be considered including those I have not thought of.

Radiator, thermostat, plugged cooling system, fan clutch, too much water and not enough anti-freeze lowering boiling point, timing, computer etc. You need this vehicle looked at by a professional, otherwise you are going to replace good parts on a guess and could get very costly.

WARNING: This is the ht-4100 aluminum engine. If the temp gauge goes above 3/4 you are causing this engine to self destruct in a major way. Head gaskets, cracked heads, cracked block are very common from overheating and I handle about 3 engine damage questions a week on the aluminum engines put out from 1982 to present by Cadillac.

People think these are like the old Chevy cast iron engines you could get away with overheating. Worse yet, chances of finding a good used engine is slim to none!!

I know you won't like this, but please remember I did not engineer or build this problematic engine. Until you get it fixed, keep the temp gage between 1/2 and 3/4. If thus means you can't run the A/C so be it. Don't think I do not understand. I am in Texas and it has been over 100 forever it seems.

If it starts getting hot and keeping the A/C not running does not help, you can turn on the heat so it can circulate and keep the engine cooler. If the temp goes to the red, your engine WILL BE BEYOND REPAIR!

Good Luck!


If my answer assisted you, please rate it.

Thanks,

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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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