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Carguyjosh, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 2172
Experience:  ASE certified tech, 17yrs experience
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2000 Cadillac Deville: overheating..radiator, water pump..flushed

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I have a 2000 Cadillac Deville, 4.6L Northstar engine. I have an overheating problem. I have replaced: radiator, water pump, thermostat, water temp sending unit, flushed cooling system & followed manual for refilling cooling system. Pressure tested system & rad cap. No leaks/cap OK. No excessive radiator pressure (13lbs) when the engine is running or when "gunning" the engine. Both electric fans working & all shrouds/panels are in place. The engine does not overheat while idling or cruising on a level surface with A/C on. When the car goes up a hill the temp gauge starts to climb towards red zone. Once the hill is peaked engine starts to cool down. I can go into neutral and rev the engine & temp goes back to normal (mid range on temp gauge). Tested thermostat opens @195F. I have used a lazer temp gun & when the engine is hot the hose from the radiator to the thermostat is about 135F. When the engine is at normal temp this hose is 175F. Head gasket? Thoughts? Thank you.

Unfortunately, it sure sounds like the beginning of a failing headgasket..

When higher stress is put on the engine, the cylinder temps are higher and allow exhaust gas into the cooling system.

What I would recommend is that you go into the shop for a cylinder block test. What this test checks for is the presence of exhaust gases leaking into the cooling system.

If the engine fails the block test, then you will need to make the decision of if to have the engine torn down or not...

I definitely think that you are on the right path with your though of bad headgaskets...

Thanks Carguyjosh
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