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Overheating

Tiny
COREY H JENKINS
  • MEMBER
  • 1996 CHEVROLET TAHOE
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
Truck ran fine last night no problems.
It got down to twelve degrees last night but I had plenty of antifreeze.
Cranked it this morning and it started overheating. Seemed like the pressure was pushing coolant to reservoir and out overflow tube.
Changed thermostat replaced coolant and still does the same thing.
Does that mean it is my water pump?
Any way to test it?
What else could it be?
Do I need to run it without a thermostat?
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Monday, January 1st, 2018 AT 12:19 PM

13 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

Several possibilities:

check the cap on the radiator.
Head gasket may be leaking compression into the cooling system. A leak down test will confirm. That is when the remove the plugs and inject air into the cylinder and watch for coolant movement in the radiator.

Roy
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Tuesday, January 2nd, 2018 AT 3:54 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
What am I checking the radiator cap for?
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Tuesday, January 2nd, 2018 AT 3:59 AM
Tiny
ASEMASTER6371
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To see if it holds pressure. You would need a radiator cap pressure tester to confirm.

Roy
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Tuesday, January 2nd, 2018 AT 4:01 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
What would cause head gasket to go bad?
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Tuesday, January 2nd, 2018 AT 4:28 AM
Tiny
ASEMASTER6371
  • MECHANIC
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Hard to say exactly. It could be from a previous overheating condition or the weather may have had a roll in it. If you are going to have it repaired, once the head is removed the tech should be able to give you an idea of why it failed.

Roy
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Tuesday, January 2nd, 2018 AT 4:32 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
Is there some other way to check head gasket besides putting air into spark plug hole and checking for movement in radiator? Too cold to put water in radiator and I have no way to pump air.
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Tuesday, January 2nd, 2018 AT 4:44 AM
Tiny
ASEMASTER6371
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They do sell chemical kits at parts stores, but I have found them unreliable. The leak down test is the most exact test for the failure.

Roy
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Tuesday, January 2nd, 2018 AT 4:46 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
On the leak down test, is it just one plug hole or do I need to do them all? If only one, any one in particular? Can I just get an air nozzle on a air compressor or do I need an attachment to screw in the plug holes?
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Tuesday, January 2nd, 2018 AT 4:54 AM
Tiny
ASEMASTER6371
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All cylinders need to be done.
I use a compression tester and remove the valve from the end. Makes it easier as it is difficult to get to all the cylinders with the straight tip. You can rent one at a parts store.

Roy
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Tuesday, January 2nd, 2018 AT 4:57 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
What are the chances of it being water pump? What would be signs of it being pump?
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Tuesday, January 2nd, 2018 AT 5:35 AM
Tiny
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Not a water pump. It would not push back through the surge tank. This is higher pressure.

Roy
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Tuesday, January 2nd, 2018 AT 5:45 AM
Tiny
COREY H JENKINS
  • MEMBER
  • 80 POSTS
Thank you for all your help and knowledge. One last question, I have always heard if head gasket is blown there would be water in oil. Is that true?
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Tuesday, January 2nd, 2018 AT 5:54 AM
Tiny
ASEMASTER6371
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Yes, it takes time to mix with the oil. Then the oil will become milky. You may or may not see it.

Roy
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Tuesday, January 2nd, 2018 AT 5:57 AM

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