Overheating Caddy

DKEGARIE

MEMBER
2001 CADILLAC DEVILLE DTS
V8
FWD
AUTOMATIC
95,000 MILES

My 2001 Caddy DTS overheated due to low coolant and the alarm went off (sensor in overflow bottle not working). I pulled over and turned car off immediately. I Topped fluids up. Took to dealer and was told I needed a new radiator and new gaskets around the water pump housing ($2,100 to replae radiator/fix gaskets). I was told both housing and radiator had small leaks, but pump is OK (replaced 3 years ago). After filling coolant up and running, it still starts overheating. So I had the worst leak (I saw no coolant leaking) fixed by replacing the radiator ($950+). I took it home Saturday, but it is still overheating somewhat when going up hills. No signs of any coolant leaking. Radiator cap replaced 1 year ago and supposedly
still good. I can see the overheating by watching the temperature gauge, which runs fine for a while, and then jumps up a bit and then back down and then back up a bit, and up a bit more if going up a grade.

What is the problem? Could a minor leak in the water pump housing gasket(s) cause loss of pressure and cause overheating to show on temp gauge? (Dealer says $1,000+ to fix gaskets.) Could my problem be caused by faulty thermostat that maybe got damaged by the initial overheating? Would the electronic sensor be damaged? Any ideas will be greatly appreciated.

Thanks, Caddy Fan

6 Replies

FACTORYJACK

MECHANIC
4,159 POSTS

Often times the coolant level sensor sticks reading low level when it is actually full, but that is beside the point. Low coolant certainly could lead to an overheat, but I don't think that is your problem. A thermostat is most likely going to overheat an engine quickly if it is stuck closed. You have another variable that needs to be addressed, and I am surprised the dealer has yet to test it. You need to have the cooling system tested for the presence of combustion gases, indicating an internal leak. It is very common for the head bolt threads to pull resulting in an internal leak through the head gaskets. This overheating condition, is going to be more noticeable when the engine is run harder, as the load is increased. The test is best performed with a gas analyzer, from a cold start, after a hard run. Use the analyzer to check as the radiator cap is initially removed. There is always going to be some hydrocarbons in the system, a small amount(1-10 ppm). It is when you start seeing the large numbers(100-300 ppm), that you know there is a problem.

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Monday, August 8th, 2011 AT 4:43 PM

DKEGARIE

MEMBER
3 POSTS

Thanks very much gstacey. The dealer told me they checked the block and there was not a problem with the head bolts, ie-no leaking of fluids into the combustion chamber, which I think I would notice as rough engine running (engine runs fine). I don't know if they used a gas analyzer. They seem to be anxious to replace parts. I'll ask them to do that, but what else might it be if not that?

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Monday, August 8th, 2011 AT 4:56 PM

CADIEMAN

MECHANIC
3,544 POSTS

They should have had to replace the water pump assy not just gaskets. If its bubbleing in the coolant jug it may be a head gasket. Check that all fans are operating properly.

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Monday, August 8th, 2011 AT 5:12 PM

DKEGARIE

MEMBER
3 POSTS

Thanks Cadieman. Fans appear to be running OK, as they run when car is sitting in the shop. No bubbling in the coolant jug, it was replaced and coolant and level looks fine.

Could a small leak in the water pump housing (or water pump) cause enough of a loss of pressure in the cooling system to cause overheating? The coolant levels are fine. Very frustrating issue.

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Monday, August 8th, 2011 AT 5:34 PM

CADIEMAN

MECHANIC
3,544 POSTS

You would see the coolant if it was leaking. You need to check the flow. When the thrmostate opens the upper hose gets hot as it goes from the engine to the radiator. Remove the cap and check for flow through the radiator tubes as you rev the engine up and the thrmostate opens you will see flow in the radiator.I dont no why they didnt replace the thrmostate first.