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  1. #1

    Default why am I leaking coolant at the drain plug

    I'm loosing coolant. The thermostat is working. The water pump is not leaking and the engine stays cool (when it has coolant) but after a good drive 15 mi. or so the radiator is steamy and coolant is pouring out of my drain plug. PPPPPPPPPPPPPPLEASE help.


  2. #2

    mfleetwood's Avatar
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    Jul 2010
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    If it's leaking out of your drainplug, could the plug be cross-threaded or somehow not properly sealing, thus when pressure builds fluid escapes through there? Have you checked/replaced your radiator cap or are you sure it has the proper pressure relief? How long has this been happening or did you do any work to your vehicle right before the problem started?

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  3. #3


    Thanks for the reply. The radiator cap was my first move. I replaced the drain plug with one from my local Chevy dealer and took a test drive. Everything seemed fine but one more drive to work resulted in more coolant comming from the drain plug. It must be leaking while I drive. While idling in the driveway, no leak is evident. I'm befuddled. Would the water pump weap while just on the road? It's a 99 C/K 1500 with the 5.7.

  4. #4


    Another place you might check for leaks is the cooling lines that connect to the radiator from the transmission.

    2008 Ext. Cab Silverado LT1 5.3L 2WD
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  5. #5

    mfleetwood's Avatar
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    Because of your question regarding it possibly leaking from the water pump, it sounds like you are not 100% positive it is actually coming from your drain plug?

    Water is a funny thing and will follow a trail and many times drip from the trail's lowest point. Untouchable is correct in asking if it could possibly be coming from another source. It could be welds for your radiator hose connects, hose not fully sealed/clamped, cracked/leaking hose, pin hole in radiator. There's a lot of flow and pressure when the RPMs are high, and water is circulating and heating up, thus the leak may not present itself until the tougher circumstances present themselves (more than idling).

    If by close visual inspection, you still cannot find the leak in any of those other areas or in areas in which a water trail could lead to your plug, you might want to try a pressure test. Here is an article that may help you if you get to that point.

    Pressure test to identify any external leaks:
    Pressure testing the cooling system is a simple process to determine where a leak is located. This test is only performed after the cooling system has cooled sufficiently to allow you to safely remove the pressure cap. Once you are sure that the cooling system is full of coolant, a cooling system pressure tester is attached in place of the radiator cap. The tester is than pumped to build up pressure in the system. There is a gauge on the tester indicating how much pressure is being pumped. You should pump it to the pressure indicated on the pressure cap or to manufacturer's specs.

    Once pressure is applied, you can begin to look for leaks. Also watch the gauge on the tester to see if it loses pressure. If the pressure drops more than a couple of pounds in two minutes, there is likely a leak somewhere that may be hidden. It is not always easy to see where a leak is originating from. It is best to have the vehicle up on a lift so you can look over everything with a shop light or flashlight. If the heater core in leaking, it may not be visible since the core is enclosed and not visible without major disassembly, but one sure sign is the unmistakable odor of antifreeze inside the car. You may also notice the windshield steaming up with an oily residue
    __________________________________________________ _______________________________________

    One thing that I will add to this article is that if leak is higher than the liquid may be (i.e top of radiator hose weld) then it might not leak fluid when the pressure is applied, but leak air. Double check those types of areas using a vacuum hose and then try listening for the air leak.
    Last edited by mfleetwood; 01-26-2012 at 06:37 PM.

  6. #6


    Pressure Test the cooling system. Most auto parts stores will loan you one of these. some will actually walk out nd test your system at the store@no charge
    A a parts store manager we would test cooling, battery and starter at no charge
    2010 Chevy Silverado Z71 ext cab.4x4
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