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Cadillac Repair/1998 Cadillac Seville overheats


we took off the radiator cap added one half water one half coolant ran engine and level stayed same.
overheats. could this be a water pump failure or a thermostat?
where is the thermostat?
can i buy one and put it in? easy fix or not?


Warning--if you overheat one of these aluminum engines, the engine literally melts! If the temp reaches 225 degrees or the hot light comes on, damage is already starting. The result is at minimum a $1,500 head gasket replacement, worse yet, that is the result and not the cause. You will not find a good used engine in a junk yard because they have all been driven hot.

Everyone changes the thermostat and that never seems to be the issue. It is located on the engine end of the upper radiator hose.
At times, there are water pumps that break the internal fins, but these aluminum engines are subject to many different overheating issues. Far too numerous for me to rap off.

The cooling jackets in the engine are small and to give you and idea as to how sensitive these engines are, if the water pump is changed and a small piece of old sealant or gasket is left inside, it will stop circulation and overheat.
I have been dealing with these issues since 1982 when Cadillac first introduced the 4.1 (4100) and these issues go all the way into 2013, on many more makes and models using the aluminum engine. They are lighter than cast iron, get better mileage and have a lot of power, but overheating is the Achilles heel to these engines.

The first thing to do is keep it simple--Warm engine-check the circulation in the radiator. Are the upper and lower radiator hoses equally as warm? Is the top and both sides of the radiator the same warmth? urn on the defroster. Does the engine fan come on? Have the radiator cap checked. For the cooling system to circulate, you need 15 pounds of pressure.

Now, if the engine is warm at the bottom radiator hose and the top hose is easily squeezed and cold, you may consider a thermostat change.
You could also have a restriction in the cooling system that a power flush of the cooling system may free up.

These are not like a cast iron 3.8 where you can drive the car with no fluid in the radiator for 20 miles and have steam rolling from under the hood. I have had to do that on a 225,000 mile Buick, and did absolutely no damage. Your engine in that situation would go about 3 miles and be junk!

Try my suggestions. If you have questions, I will see if I can walk you through the problem. I have fixed many over the Internet before it was too late.

Good Luck!

Since I answered your question so fully, I hope you don't mind a little piece about our business to our followers.


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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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