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Thread: cooling system high pressure and losing coolant

  1. #1
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    Unhappy cooling system high pressure and losing coolant

    I have a 2002 Chevy Silverado with 6.6 Diesel LB7. Have excess pressure in cooling system , losing coolant, does not over heat. I also had a oil test done for coolant in oil, none found. Tested coolant for exhaust neg results. I am leaning towards headgaskets or a cracked head. Any ideas out there?

  2. #2
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    If you are loosing coolant in small amounts over time and not over heating I would suggest replacing the coolant pressure cap. They are inexpensive and a good starting place to look for the cause. My 2006, LBZ was using small amounts of coolant for several years and a new pressure cap solved the problem.

    Good luck
    John
    *2006 Chevy, 3500, 4X4, DRW, (LBZ) D/A, CC, LT, 252K Miles, 19.5" Wheels, Mag Hytec Transmission Pan and Differential Cover, SS Grill Guard, Racor 2 micron aux fuel filter, 100 Gallon Aux Fuel Tank, using Edge Evolution, Predator Diablosport, Kennedy ECM tune, Fitch Fuel Catalyst.

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  3. #3
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    A typical cooling system will reach a pressure of 8-10 psi at operating temperature. After sitting overnight and the engine cools completely, that pressure should drop to near zero. A cooling system that holds significant (a few psi) pressure overnight indicates a problem with combustion pressure finding its way in to the cooling system. Jim

  4. #4
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    May 2012
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    Langley
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    I had something similar for a while. I bought a new cap and I also had a collapsed upper rad hose.

    Seemed fine for awhile, then had additional issues.

    Eventually (over a couple of years) it lead towards head gasket failure

    Hopefully yours goes somewhere else!
    GMC Sierra 2500hd 2004.5 now with ARP studs

  5. #5
    Join Date
    Jan 2006
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    South Milwaukee, WI
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    Hope you got 'er fixed by now but man, this sounds really familiar. About 2 years back I had the same thing with an '01 LB7 and it turned out to be a leak at the #7 cylinder- bad head gasket. And this, after a new set of head gaskets that were replaced about a year earlier. I took Kennedy's advice and bought a set of studs- no more OEM head bolts. And no further leaks.
    "Chessy56"
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

  6. #6
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    Arrow

    Quote Originally Posted by chessy56 View Post
    ... I had the same thing with an '01 LB7 and it turned out to be a leak at the #7 cylinder- bad head gasket....
    How many miles did the engine have on it - with head bolts - before the head gasket failed the first time?

  7. #7
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    Jan 2006
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    The first time it failed, I had ~338K miles on it. I saw leakage from below around the #1 cylinder. It hadn't totally failed yet, but the evidence was clearly indicating a leak was in the making (it had the original head bolts). The (2nd) leak was at the #7 cylinder and it occurred at ~401K, less than 2 years later. It now sits idle with ~437K miles on it. I had studs installed during the 2nd HG replacement.
    Last edited by chessy56; 07-02-2017 at 17:38. Reason: additions....
    "Chessy56"
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

  8. #8
    Join Date
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    Montana
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    Quote Originally Posted by chessy56 View Post
    The first time it failed, I had ~338K miles on it. I saw leakage from below around the #1 cylinder. It hadn't totally failed yet, but the evidence was clearly indicating a leak was in the making (it had the original head bolts). The (2nd) leak was at the #7 cylinder and it occurred at ~401K, less than 2 years later. It now sits idle with ~437K miles on it. I had studs installed during the 2nd HG replacement.
    So, 338K miles on the original head gaskets and original Torque-to-Yield (TTY) head bolts... Sounds like good service to me. Properly prepping the head and block deck surfaces during a head gasket replacement is important to long-term reliability.

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