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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 6286
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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I have a 1998 Cadillac deville overheating.Thermostat is ...

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I have a 1998 Cadillac deville overheating.Thermostat is not the problem, down thew road in excess of 45 the car runs about normal operating temps. It overheats in stop and go driving. I just noticed today after my wife shut it off,that neither of the fans were running with a coolant temp of 230 F. I have alldata and notice that there are three fan relays. Why 3 relays and how would you go about testing fan motors? After warm up it runs down the freeway at 65 at about 195 to 222 degrees F. depending on the ambient temp. lately it's been around 90 or more degrees. I washed out the rad. fins real well and hoses all look good
Odds are that the problem is in the electrical system, and not the fans. It is very unusual for both fans to go out at once. The wiring for this system is a little complicated for a fan system. The powertrain control module is what triggers the relays to turn the fans on. There are two fuses that can affect the system. If the ac compressor fuse blows them the fans will not come on when you turn on the compressor like they should. There is another fuse located in the passenger side main fuse block that will shut the while system down if it Blows. This fuse is 50 amps. I would check these fuses first. If the fuses do not work the next item I would suspect is the relays. Here is a wiring schematic of your system. This will be helpful if anyone needs to repair the wiring on your car.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.
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Customer: replied 9 years ago.
I spoke with a friend moments ago and he asked how it all happened. I told him that my wife complained that her A/C was inop. The car has 180000 mile on orig. compressor.Well,the compressor seized when I attempted to add refrigerant.So, I pulled the A/C fuse to avoid compressor ops. while it was seized.That is the same time that my overheating problem began.This is when my friend says he believed that the fans are operated, as you said, in the same circuit as the A/C fuse.I've replaced the fuse, but the car is at the curb reading about 150 degrees F. I guess I'll have to run it down the road to see if this fixes the problem.
Ok good luck.
Customer: replied 9 years ago.
I still haven't taken the car for a test ride, but by looking over the schematic that you enclosed and following my friend's and your own advise, I believe that it all makes sense. I'll give it a try shortly.For now I will gladly accept your answer and thank you very much.
Ok, best of luck.
Customer: replied 9 years ago.
By now you should know that I accepted your answer. I test drove the car a bit, not hard, but I drove around town a bit and reached 197 degrees F. When I got home and parked I left engine running and found both fans not operating, however I do not know what the operating temps are for the fans. Everything seemed to operate fine on my test run. I'll keep an eye on it and see what develops. Thanks again my good man. Wayne Cunningham
Ok Wayne best of luck.