1997 Chevy Monte Carlo Does not warm up at idle

1997 CHEVROLET MONTE CARLO
79,050 MILES • 6 CYL • FWD • AUTOMATIC
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SCOTTSPEER
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Recently replaced water pump. Now when car is started in the morning, the heater does not get warm. When you drive it the temp gauge will go up way above normal and then drop back down to below operating temp then slowly go back up to operating temp and the heater will warm up. The gauge will then float up and down and finally stabilize and heater works fine. I have noticed that when I stop and check the overflow bottle, it is full and sometimes overflowing. When the car is cold, the bottle is at the cold level as it should be. Also seems that if you loosen the radiator cap, a lot of air comes out of the system. I have bled it using the bleeders at the thermostat and water pump, have tried to get the air out by leaving the cap off and idling the car, adding coolant when the leve drops. When I do this though, the radiator overflows and then drops and then overflows and drops again, loosing a lot of coolant. There never seems to be just a constant flow through the system. What could be causing this?
Dec 12, 2009 at 8:53 AM
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JACOBANDNICKOLAS
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You have an air block. In the system, even though you bled it, there is still air. You need to continue trying to bleed the system to get all of the air out.

However, I need to know one thing. When you start the engine cold, if the radiator cap is off, does it blow coolant out?
Dec 13, 2009 at 1:13 AM
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SCOTTSPEER
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In less than a minute the coolant level raises and begins to overflow the radiator at a slow but constant speed. If you let it run a little longer, then it becomes more drastic with a more surging motion rising and then falling with a lot of air bubbles.
Dec 13, 2009 at 9:13 AM
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JACOBANDNICKOLAS
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Based on your description, I think you have a bad headgasket. I would recommend having the compression tested. However, when the coolant starts getting blown out when the engine is cold, it is usually due to pressure in the system that shouldn't be there. Have you noticed if the engine oil has any coolant in it?
Dec 13, 2009 at 12:44 PM
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SCOTTSPEER
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No water in the oil, white smoke or even miss in the engine. But I will have the compression checked as you suggested.
Dec 13, 2009 at 2:26 PM
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JACOBANDNICKOLAS
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Let me know what you find and thanks for using 2carpros.com

Joe
Dec 16, 2009 at 9:04 PM