1. seabee

    seabee FABO Gold Member FABO Gold Member

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    My rear exhaust bolt has been hissing and I recently took it out cleaned it up and used Peramtex ultra copper on it. The next day when I started the car there was a stream of coolant squirting through the overflow tube in a timed sequence. The car was only on for 20 seconds or so before turning it off. Everything was cool to the touch but when I twisted the cap off it exploded coolant fluid all over the garage. There was some serious pressure! The coolant was room temperature so I think it is not a thermal issue but it is being pressurized by a cylinder and that explains the timed sequence of squirting through the overflow tube.

    There is no coolant in the oil/ vice versa. No smoke or water coming out the exhaust. Compression test is normal on all cylinders. The only thing I can think of is a breach between the exhaust port and coolant passage that is sending exhaust pressure into the coolant.

    I plan on replacing the rear exhaust bolts with studs and new gaskets but before I reassemble and try again would like any input on if this might be a cracked head.

    Any thoughts?
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Definately cylinder pressure. This does not necessarily mean a blown gasket or cracked head. It could also be a cracked block/ cylinder wall. First order of business is to see if there's coolant in any cylinders.
     
  3. crazy 340

    crazy 340 Well-Known Member

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    compression test

    if no sign fluid in the cylinder
    put an air pressure on each cylinder using the spark plug hole
    120 psi at least with the rad cap off
    see if there is air coming to the rad
    if not you are good to go

    even there if there is no smake to the exhaust
    I dont think it have a leak comp.to prestone

    my 2 cents

    bob
     
  4. Mad Dart

    Mad Dart Nothing to see Here!

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    Have your factory heads been ported at all? Maybe they got close to the water and now it has cracked?
     
  5. seabee

    seabee FABO Gold Member FABO Gold Member

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    Thanks for all the tips....

    MD, yes the heads were ported so maybe it developed a breach is what I am thinking.

    So far no coolant in the cylinders and my leakdown test showed no leaks to the radiator. Borrowing a radiator pressure tester today and will post results...

    Thanks agian
     
  6. seabee

    seabee FABO Gold Member FABO Gold Member

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    So the mystery continues..............

    Put pressure into the radiator until the hose were taught and left it there for half an hour. Came back and the pressure tester gauge has exactly the same reading. I turned the crank to a few different settings to see if the valve or piston positions would reveal a crack but no change in pressure.

    I did put a new water pump in when replacing the timing chain. The new pump had an extra outlet but came with plugs. I put the hoses back to the same configuration as the last pump and plugged the extra (see picture).
    [​IMG]
     
  7. SGBARRACUDA

    SGBARRACUDA ROY FABO Gold Member

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    I'm thinking if there is a small crack in the exhaust port above the valve or maybe in the valve seat, it might not show up until the head heats up as in when it is running before the gasses find their way to the coolant passage?
     
  8. seabee

    seabee FABO Gold Member FABO Gold Member

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    Lol that sounds about right when it comes my car. Never the obvious symptom or remedy but some random, sporadic, mis-hap that makes me scratch my head for a month.

    I upped the pressure even further on the radiator pressure tester and left it for a while and still no leakage. When this happened before it was at a cold start and only for 20 seconds or so. I have lot$ invested in these heads so praying it's not them.
     
  9. Mad Dart

    Mad Dart Nothing to see Here!

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    Sounds like above When heat is in it the pressure is finding its way into the crack. Some good epoxy would probably fix your problem. You may even be able to do it in the car with the Manifold/headers pulled back or off.
     
  10. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    You might have something like a crack in a head or cylinder wall which opens up with heat, and the pressure you can bear on the rad will not show that

    Rig yourself a spark plug air supply, take the check valve out of your compression tester, etc, and air up one cylinder at a time and see if you get bubbles back into the rad.

    If you pull the valve gear loose, you can air them up at bottom dead center, with the valves closed. That way the swept area of the cylinder wall will be exposed.
     
  11. seabee

    seabee FABO Gold Member FABO Gold Member

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    This is similar to what I did earlier today but without the water in the radiator. I loosened the rocker shafts so all valves were closed then put 100psi into the cylinders which would bottom them out and then listened for leaks in the radiator. Tomorrow i'll fill it back up and check for bubbles.
     
  12. seabee

    seabee FABO Gold Member FABO Gold Member

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    Filled with water and pumped air into the cylinders today. No bubbles. Pumped psi into the coolant system and it held steady.
     
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