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Cadillac Repair/Loss of coolant


Hi, I recently bought a 1997 Cadillac Deville with 111,000 miles on it. Everything in the vehicle looks and runs great, but it slowly loses coolant. I have to add almost a gallon of coolant per tank of gas. I have taken it to 2 shops. Both places pressure tested the system and told me the same thing, that the pressure initially holds but then decreases very slowly and neither of them can find any leaks. Is my engine burning of the coolant? Any ideas on what might be going on?




Here is the bad news: A Cadillac aluminum engine can never be over heated. With a 50/50 coolant mix, if the engine reaches 220 (I say that for safety) that engine needs to be shut down immediately! These engines are unforgiving and begin to melt at 225 degrees.

They have a whole host of cooling system issues and it can be something as minor as old water pump gasket remains to plug the water jackets in the engine. A good used engine at a junk yard is impossible to find because a majority have been overheated and generally the only answer for the repair of a vehicle with a severely overheated engine is a $4,000.00 GM crate engine.

I list all this so you are aware of what you are dealing with. In the archives I probably have over a hundred questions I have answered on Cadillac cooling system issues.

Just because they can't find a leak, does not mean there isn't one. I wonder who taught the people at both shops as to how a cooling system pressure system tester actually works. I do not say this to be mean. I say this because they are probably not familiar with the Cadillac aluminum engine and the problems associated with it.

You did not state as to how slowly it looses pressure. It is not supposed to loose pressure until the engine is cool. Now, this is what concerns me: These engines are notorious for head gaskets, which is never the cause of an overheating situation, but the after effect.

If it is losing pressure and a trail cannot be seen, you either have a blown head gasket which would cause you to burn coolant in this case, or you have a cracked block.
Did anyone check the oil? If its white and milky colored, your coolant is going into the crankcase. If you are burning it, depending on the leak, you may see why smoke, but if you get near the tail pipes, you may smell a sweet smell with the engine running.

Also check the passenger floor carpeting for a wet sticky feeling which could be a small leak in the heater core and if they are checking the engine area, they obviously would not be looking there.

You have a leak and if you need head gaskets your are looking at about $1,500.00. Heater core replacement is pricey as well, but you need to find the problem.

Good luck and let me know what is found.

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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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