I have a 2000 DeVille with an intermittent over heating problem. It has a new water pump, radiator, and thermostat (replaced three times). The cooling system has been flushed, pressure tested with dye and no leaks were found. There are no traceable coolant gasses in the exhaust and it’s not losing water either. Any ideas on what could be wrong?

 

Are the fans coming on?

 

Yes, both fans are working like they should.

 

Do you have coolant or water in system? How is your pressure cap?

 

Uhhhhh----yeah! LOL
I guess you just wanted to cover everything!

The cap is original but it looks like it is okay. I have taken it to two different shops. One is a NAPA shop and the other is a guy that I have been taking my cars to for 25+ years. I actually moved away from his area 15 years ago but I still use him and he is 72 miles from me. I trust him, can you tell? Anyway, we are all stumped. It would be different if it always ran a little hot but it doesn't. Originally the water pump was leaking, so it was replaced along with the thermostat. Then I found a small leak at the top passenger side of the radiator. I took it to my favorite mechanic (72). He flushed the cooling system and replaced the thermostat again (at no additional cost) because he said the other one was cheap and he didn’t want to take a chance with it. So after the flush was done, the new radiator was installed. As I was driving home, about 40 miles out the gauge went to one bar above normal. I let it cool and then checked the water level and it was fine. Drove another 5 miles or so and it went back up again but before I could get pulled over it went back down to normal. It did the same thing the rest of the way home. I took it out and drove it again the next day and it was fine. I drove it another week and still everything was fine. I took a vacation trip and put 2,206 miles on it (@ 23 mpg average) and everything was fine. Two days later it was back at it again. That’s when I took it back to NAPA and had the pressure test done and they tested the exhaust gasses, replaced the thermostat AGAIN just to play it safe. I drove the car that night and put another 120+ miles on it and all was well. Got up the next morning and made it all of 7 miles and it started to show a little warm again. This time two bars above normal. I had it taken to NAPA again (I love Triple A) and they let it sit and run for three hours in 90+ temps and can’t get it to move above normal. I think I have officially driven them crazy with this Caddy. Can you guess who is next? LOL
Could it really be something as simple as the cap?
Thanks for your replies!

 

Well i meant to ask if you had ANTI FREEZE or just water in the system. When the car gets hot are you climbing hills, a/c running or sitting in traffic? Has it actually overheated?

 

Anti freeze mixed with water and it has happened on hills and flat roads. It has never overheated!

 

Did you test to for exhaust gasses in the coolant? I see you wrote they tested for coolant coming out of exhaust. To me it sounds like a possible head gasket problem. You replaced everything that there is to replace. You sure the fans are working properly? Are they coming on when they should be?

 

They didn't say that they had tested for exhaust gasses in the coolant but I will check with them. If that was a problem and if I let the motor run with the radiator cap off, would I see air bubbles coming up through the coolant? The fans have been checked and I have been told that they are working properly. I can see for myself that the come on before it reaches the normal operating temp. If it was a problem with the head gasket, wouldn't that create a continuous problem?

I picked it back up from NAPA today; they had to replace the rotors that they installed less than three months ago because they had warped. I went ahead and picked up a new radiator cap ($4.79). I am REALLY hoping that it is something this simple. I’ll never let them live it down! LOL--- I’ll see how things go!
Thanks again for taking your time to try to help me out!
Mark

 

So far so good!