Blown Head Gasket???
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500, 472, 425, 368 Discussion, Blown Head Gasket??? in Cadillac Engine Technical Discussion; I have been working on the 1976 Eldorado investigating the oil burning issue. I don't know the history of the ...
  1. #1
    davidp1561 is offline Cadillac Owners Member
    Automobile(s): 1976 eldorado convertible
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    Blown Head Gasket???

    I have been working on the 1976 Eldorado investigating the oil burning issue. I don't know the history of the motor how it was cared for or maintained etc. It shows 78,000 miles (approx.) but could be 178,000 or 278,000 who knows. Here is what I have found so far......

    It burns oil - bluish smoke from tail pipe
    Runs rough seems to be missing
    There is no oil in the antifreeze
    There is no anti freeze in the oil
    Put in new plugs and ran the engine for about 20 mins
    Pulled all the plugs and performed compression check on all cylinders and found:

    cylinder #1 = 150 psi
    #3 = 150 psi
    #5 = 140 psi
    #7 = 145 psi
    #2 = 87 psi
    #4 = 119 psi
    #6 = 149 psi
    #8 = 146 psi

    When I pulled the plugs the two from cylinders #2 & #4 were the cleanest they looked to me like they did not fire.

    My questions are: Does this look like the problem is a blown head gasket? A valve issue? A combination of both? Or something totally different?

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  3. #2
    deVille33 is offline Cadillac Owners Connoisseur
    Automobile(s): 1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
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    Re: Blown Head Gasket???

    By your observations, I would say, your assumptions are correct. The head gasket on that bank has deteriorated and the coolant is getting drawn into the cylinders on the intake stroke. More on # 2 than # 4. This happens for basically one reason. Someone did not change out the antifreeze like they should have. The antifreeze turned to acid and ate out the head gasket. I advise changing both head gaskets and check your timing chain. If you suspect the chain, tear off the front cover and address that too.

    ----------

    Just realized this post was related to your other post. If this engine sat any length of time with anti freeze in the cylinders, it is possible the piston rings were compromised. this could be the reason for your oil use. The prognosis does not look good. Pull the head on that bank and inspect the cylinder walls on # 2 and # 4. A gouge down the cylinder wall will reveal how extensive a repair will be necessary. No gouge, drop the pan and pull # 2 and #4 pistons and inspect the rings, ring lands. Any damage to the piston tops will be evident upon pulling the head.

  4. #3
    davidp1561 is offline Cadillac Owners Member
    Automobile(s): 1976 eldorado convertible
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    Re: Blown Head Gasket???

    Thank you for your insight. Will post more as things progress

  5. #4
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Blown Head Gasket???

    I wouldn't be so quick to blame the head gasket. We don't know how long the car has been sitting. I wouldn't pull the head unless I knew I was losing coolant somewhere or the radiator was getting over-pressurized. It could just be some stuck rings on those 2 pistons. Most likely the valve guides are toast causing some or most of that blue smoke. I would drive it like a teenager for a few days and see if it comes out of it.

  6. #5
    davidp1561 is offline Cadillac Owners Member
    Automobile(s): 1976 eldorado convertible
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    Re: Blown Head Gasket???

    I know that the car sat for some time. I know that there is no antifreeze in the oil and no oil in the antifreeze but haven't done a check to see if the radiator is being over pressurized. How would I check the radiator for that?

    ----------

    Also, would stuck rings and bad valve guides cause it to run rough like it is missing?

  7. #6
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Blown Head Gasket???

    If there was only oil in these cylinders, the plugs would have been oil fouled. Water or coolant in the cylinders will clean the piston tops and spark plug. Ok, lets back up. You did not mention any noticeable coolant volume loss. If your system is being over pressured, you will see a column of steam when you stop at a light. Exhaust gasses in the cooling system will cause overheating. Take the car to a radiator shop and have them check your radiator cap to see if it is holding proper pressure. Then have them check the system, pressurize it to determine if it has any leaks. If it doesn't hold pressure, coolant is going somewhere. I have seen head gaskets go that allow coolant to be sucked into the cylinder, but not allow combustion gasses into the cooling system. ------------------ Stuck rings will allow oil into the cylinders and will allow fuel to wash down past the rings when on the compression stroke. Is the oil thinned out? Does it have a gas like odor? Stuck rings can also cause any combustion of the fuel mix to blow past the rings and burn the piston lands. Racing the engine, under load, may loosen things up, but there is no guarantees. --------------------- If you have an air compressor, you can use your compression tester, if you have the type with the quick disconnect fittings, to check your cylinders for leak down. Connect your pressurized tank to the tester lead, with the piston at TDC on the compression stroke and listen for the air. If the air goes to the oil pan, your rings are your problem. If the air goes to the exhaust pipes, your exhaust valve is your problem. Back through the carb, your intake valve is the culprit.

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