Bleeding the cooling system

LELLSWORTH

MEMBER
2003 CHEVROLET SILVERADO
V8
4WD
AUTOMATIC
165,000 MILES

I recently replaced my head gaskets due to pressure in my cooling sytstem. However, now I have air in my cooling system which is causing my heat to come and go. I have done vacuum and pressure tests, which show that there are no leaks in the system The thermostats are opening and closing because I have flow. However, I cannot seem to find out how it is possible that air is getting into the system. I have taken off the radiator overflow cap and let the engine idle to let any air out but the problem reoccurred. After driving a little while the air block will move and I will have heat again. Then after a little the temperature gauge starts to drop and the heat goes again. Is there any way air can get into your cooling system through the water pump?

6 Replies

BRIAN 1

MECHANIC
1,030 POSTS

Try bleeding the out of the system this way first. Start the engine.
Idle the engine for 1 minute.
Loosely install the surge tank cap. Do not allow the system to build up pressure.
Cycle the engine from idle to 3000 RPM in 30 second intervals until the engine coolant reaches 99 °C (210 °F) and the thermostat opens.
Shut off the engine.
Refer to step 2 in order to remove the surge tank cap.
Start the engine.
Idle the engine for 1 minute. Fill the surge tank to 1/2 inch above the COLD FULL mark on the surge tank.
Install the radiator surge tank cap.
Cycle the RPM. Idle the engine to 3000 in 30 second intervals until the engine coolant reaches 99 °C (210 °F).
Shut off the engine.
Top off the coolant, as necessary, to 1/2 inch above FULL COLD mark on the surge tank.
Rinse away any excess coolant from the engine and the compartment.
Inspect the concentration of the coolant.
Post back if this works.

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Thursday, December 11th, 2008 AT 12:32 PM

LELLSWORTH

MEMBER
3 POSTS

I tried bleeding the air out, but it just keeps getting in somehow.I am a GM Mechanic and I have the whole shop here at the dealership I work at stumped. Air keeps getting in and getting locked and I lose heat and temperature drops and then if I rev the truck the air will come out and I will have heat but only for a shot period of time. Since I last posted I bled the truck again, replaced thermostats, replaced water pump and sealed the gasket below the water pump because I saw a few air bubbles coming out there. I have replaced everything I can think of and it just doesn't make any sense to any of us that air can be getting in that system. The only other option I am thinking about now is whether it is possible for the turbo to somehow take air into the coolant system somehow. Any thoughts?

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Wednesday, December 17th, 2008 AT 9:58 AM

BRIAN 1

MECHANIC
1,030 POSTS

Sounds like you did alot, only other things I could suggest is maybe a leak somewhere else, or maybe the coolant sys is plugged somewhere maybe when you replaced the gaskets it shifted the the debis somewhere else. Did you use the wright head gaskets, these have 3 different ones. One other thing, what about the blend door, make sure the acuators are working maybe it's in the hvac sys and maybe not a mechanical issue. Last suggestion check for bulletins and PI"s. Also call TAC, theve helped me solve some really weird problems. This is all the help I can give without being there. Post back with what you find.

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Wednesday, December 17th, 2008 AT 10:22 AM

LELLSWORTH

MEMBER
3 POSTS

Hey, first of all Thanks for all your suggestions, I really appreciate you taking the time to help.
I cannot see a leak anywhere at all. The coolant can't be plugged because I checked the rad and the coolant is flowing fine. Yes I did use the correct gaskets. Not the actuators either. I have called Tac a few times, there are no bulletins or records of any other casese like this that have not been solved by replacing head gaskets, thermostas or water pump.

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Wednesday, December 17th, 2008 AT 10:48 AM

BRIAN 1