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Question
I have a two door 1991 Cadillac Fleetwood that continues to run hot and it hasn't got that many miles on it.  Please help!!!!!!  It is an family airloom and I don't want to part with it.  It is in great condition body wise.  Suggestions please.

Thank you,

J.H.

Answer
Hello,

Overheating is a common symptom in Cadillac GM aluminum engines. Worse yet, since all aluminum, if over 220 degree or hot light on, serious damage is occurring. The component are literally melting!
Many think thee engine are like an old cast iron Chevy engine in which the mot serious damage that can occur is possibly blowing a head gasket.
Thee aluminum engines simply cannot be driven hot and if not hut down immediately, head gaskets will blow. Heads can warp, block can crack, pistons can melt.
Head gaskets are not ever the original problem, but the result.

There are many causes for over heating to these engines, but I will tell you for a fact, the first thing replaced by many I the thermostat and that is never the problem.
The aluminum engine ha small cooling jackets in the block. something as minor as old rtv gasket sealer (just a small piece) from changing a water pump will cause a restriction.

Fans not working city driving will cause over heating. A bad radiator cap where pressure is not held will cause coolant recirculation issues. A plugged radiator can cause over heating.

Circulation is the key in these engines. Water pump impeller blades have been known to break in these engines. There are a whole host of other issues as well, so the answer to your question is not simple. I have been diagnosing these since 1982 when Cadillac introduced the 4.1 and there is never one simple answer. Especially in a case such as yours in which the engine has had overheating issues because problems cascade because of prior damage.

To make things worse, chances of you finding a good engine at a junk yard are almost non-existent because all have over heating damage. GM used to sell new crate engines for $4,000.00 and if you didn't fix the initial cause such as a plugged radiator, the new engine can be destroyed.

These were a good engine for power and fuel economy, but GM should have put a big warning on the sun visor that the second (not minute) the engine shows signs of over heating-shut down immediately! Of course the dealer made money selling engines.

To start with, you need to check the head gaskets. Pressure test the cooling system. Check the oil and make sure it isn't milky. Make sure when the engine is warm white smoke is not coming out of the exhaust. The pressure tester will show external leaks, but it won't show internal leaks like in the cylinder liner and that is why you are checking the color of the oil in the crank case. If the system and the cap are good, check the fans for functionality. Turn the engine on as well as max A/C. The fans should come on in a minute or so. Any longer, they are not working and you need to see if it is an electrical problem or a circulation issue. If the coolant sensor has no coolant circulating in the engine, the fans will never come on.
You can take the vehicle to a place that has a power flushing system and have the engine flushed, which may push out debris restricting the system.
The only way that you can determine if the plastic impellers have broken from the water pump is to remove it and inspect.

That is for starters. This is not going to be a simple venture on your part. I would also advise you to go to Ebay or Craigs and see if you can obtain a factory service manual for the vehicle.

I have been volunteering here for 15 years and what always seems to happen is that I will get a question on a subject and the subject will be the same for 3 or 4 questions even though it did not pop up for months.
The question before yours was a lady that saved her money and bought a 2001 Cadillac. The problem is she spent all her money on the car and had nothing left for any problems that popped up.

Well, she had a coolant leak and her recommended some guy probably working out of his garage to repair it. Then came the over heating. He had also done a oil change. He had the car for a couple weeks and she got the car back with the engine knocking and over heating.
He probably drove it hot too often and took out the engine. Now she has a $200,00 offer for junk for the car.

The weakest point to a Cadillac engine is over heating and repairs on these engines can quickly exceed the value of the vehicle no matter how nice it looks.

I have given you some systematic methods for diagnoses, but be aware this can be Pandora's box or a pig and a poke as us techs say. Be careful and don't let your love for the car over take your wallet.

Good luck and let me know what you find.

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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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