Will cooling system pressure test reveal a bad head gasket? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-21-2008, 01:00 AM   #1
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Default Will cooling system pressure test reveal a bad head gasket?

Just wondering if the car has a blown head gasket if they do a pressure test would it reveal the bad head gasket? Or do they have to do other tests to check for that?
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Old 02-21-2008, 01:04 AM   #2
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I bet you a bajillion dollars that it isn't head gaskets. Most likely your lower intake gaskets (LIM gaskets). 3800'* blowing head gaskets is a rarity, and 99.9% of the time you are having coolant loss problems, it is the LIM gaskets.

What exactly are the problems you are experiencing? How many miles on the car?
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Old 02-21-2008, 01:10 AM   #3
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Often the pressure test will reveal a bad head gasket. If the gasket is leaking externally, you'll see the coolant leaking outside the engine. If the gasket is leaking into the cylinders, the engine either a) won't start after having the tester on for a few minutes because now it'* hydrolocked - this is bad, or b) will have a lot of white smoke from the exhaust on restart. The only other place coolant can go is into the oil, and if this is happening you will notice the oil level has risen after the pressure test.

Another tool most shops have that I find works well is a combustion leak tester. It usually goes on top of the radiator and measures hydrocarbons (fuel) in the cooling system. If combustion pressure/gases are escaping into the cooling system, it will detect this.

From time to time I also use a pressure transducer and a tach probe with my scantool. When you suspect a bad head gasket, you can use the scan tool to graph the firing order of the engine and the cooling system pressure, and actually see on the screen the fluctuation in cooling system pressure every time the cylinder with the head gasket leak fires. Most dealerships or high end shops can do this to pinpoint the bad cylinder.

Keep in mind all of these tests don't isolate just the head gaskets themselves. Cracked heads or a cracked block are other possibilities, although not common on the 3800.

Hope this helps!
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Old 02-21-2008, 01:22 AM   #4
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Sorry, I wasn't very clear. I was just asking because so many of you are very knowledgeable and very helpful. I am not having any of these problems with my Bonneville. I just bought a Mercury 1996 Sable and read that they seem to have a problem with water pumps going out and overheating and blowing the head gasket. The water pump went out on the car the first day we drove it home and that was yesterday. The car never over heated. The shop did a pressure test on it and confirmed the water pump had failed. So I just posed this as a general question, wondering if the pressure test they performed would reveal if the head gasket had any damage because they didn't say anything about it. Sorry for any confusion.
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Old 02-21-2008, 01:27 AM   #5
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Oh, ok. You should be fine if you didn't overheat the engine. That'* usually when the gaskets go or heads crack. If it'* not burning coolant, leaking or overheating and they didn't see anything with the pressure test, you're good.
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Old 02-21-2008, 01:31 AM   #6
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Quote:
Originally Posted by Drunken Sailor
Oh, ok. You should be fine if you didn't overheat the engine. That'* usually when the gaskets go or heads crack. If it'* not burning coolant, leaking or overheating and they didn't see anything with the pressure test, you're good.
Thanks. This is hands down the most helpful forum i have ever been part of. All of you are great.

BTW, I'm having the shop replace the water pump because i didn't want to tackle that on that car. Too far over my head on these newer engines.
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