Back Pressure in Cooling System?
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Northstar Engines and System Technical Discussion Discussion, Back Pressure in Cooling System? in Cadillac Engine Technical Discussion; After running the engine for 5-10 min at normal throttle my car begins to spit out all the coolant through ...
  1. #1
    97candylacdevil is offline Cadillac Owners Member
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    Back Pressure in Cooling System?

    After running the engine for 5-10 min at normal throttle my car begins to spit out all the coolant through the overflow and then over heats. What could be causing this besides a head gasket as i dont see ANY water or vapor from the exhaust or from the side of the heads (heads to block). I did notice that it had been running the green coolant and not dex cool but for how long i dont know.

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    I_Finally_Have_A_Cad is offline Cadillac Owners Fanatic
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    Re: Back Pressure in Cooling System?

    Does this happen 5-10 min from cold?

    Open the coolant cap and start the engine. Rev a few times and look to see if the coolant bubbles.

  4. #3
    AJxtcman's Avatar
    AJxtcman is offline Cadillac Owners Connoisseur
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    Re: Back Pressure in Cooling System?

    That is only partially correct. Air will rise and if it has air in the system it will bubble. The question is how to get the Air out. After the air is gone you can check it. If you don't have a way to remove the air. You can run the engine until the thermostat opens. Then let it cool. This should remove most of the air in the cooling system and the cooling will cause the leak to be greater if it has a leak. Check the level of the coolant. Make sure it is at the full mark. Remove the system fill cap. Start the engine let it run a short time (less than 3 minutes or so). Then snap the throttle several times. If the level in the surge tank rapidly raises or you see bubbles you have a combustion chamber leak into the cooling system.
    Example of a temperature leak: Exhaust manifold leaks cold, but after the engine warms up it is quiet. Head gaskets leak all the time at -20°

  5. #4
    JimD is offline Cadillac Owners Connoisseur
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    Re: Back Pressure in Cooling System?

    Quote Originally Posted by 97candylacdevil View Post
    After running the engine for 5-10 min at normal throttle my car begins to spit out all the coolant through the overflow and then over heats. What could be causing this besides a head gasket as i dont see ANY water or vapor from the exhaust or from the side of the heads (heads to block). I did notice that it had been running the green coolant and not dex cool but for how long i dont know.
    It "could be" as simple as the air purge line is blocked somehow. And if this is a '97 Deville and somebody put green coolant in there, there is no telling what else they have been messing with.

    You will find the purge line originating at a hollow bolt in the coolant crossover directly above the water pump cover. On my engines, the hollow bolt also serves to clamp the engine lift bracket to the crossover assembly. There will be a section of rubber hose connected at the hollow bolt and the hose will eventually end up at your coolant recovery tank or pressurized reservoir depending on how GM did that in '97.

    That purge line should flow a small stream of coolant at the far end at idle. Check that first.

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