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Questions and Answers

Cadillac DeVille Is Overheating

Q. Okay I just bought a 1994 Cadillac DeVille Concours with 189,000 miles on it. I test drove it twice and let it sit with the A/C on for about 5 to 10 minutes, it never overheated. The first day I was driving it, it overheated. One day I drove the vehicle on the interstate for about 20 to 35 miles and it finally started to overheat, I was surprised it lasted that long, that lead me to believe the coolant is circulating.

Cadillac DeVille Is Overheating

So far I have a new radiator, I changed out the thermostat, I even ran it without the thermostat and it still overheated. I was going to change out the water pump but realized I didn't need to because it looked fine, the fins are still on it and it feels solid.

I changed the water pump drive belt because it was slipping a lot that still didn't change anything. Then I finally noticed that my heater core is bypassed, and the bypassed hoses sit above the engine, I was wondering if that may be creating an air pocket to cause all this. The car takes about 10 to 15 minutes to overheat unless I turn on the A/C, it will overheat quicker.

My oil has no water in it, my coolant has no oil in it, my engine doesn't miss or rock hard, both my fans are coming on when I turn on the A/C. Today I pulled out the expansion tank to check that it wasn't clogged and several other hoses, except for the hoses that run to the heater core down by the engine because I couldn't reach them.

Tomorrow I will take the radiator hose off next to the thermostat to make sure that it will shoot out liquid, carefully that is. Any help would be greatly appreciated in this matter.

  • 1994 Cadillac DeVille Concours
  • 4.6 liter Northstar 32v
  • Automatic transmission
  • 189,000 miles


A. I would take the water pump off and look at the impeller. I'm willing to bet that the impeller is worn down to almost nothing.

The bypass hose will not hold an air bubble.

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