P38 burnt out head gasket
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Thread: P38 burnt out head gasket

  1. #1
    DJB
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    P38 burnt out head gasket

    G'day, my first post after quite years of observing the issues of others and applying the results to my old girl.
    The issue I have been having with my vehicle is the pushing out of the coolant to the point where it generally has to be topped up daily. On opening the coolant reservoir there was always an escape of air/gas. I finally decided to remove the head which I suspected was the issue ( number six spark plug was wet on inspection whereas all others were dry.
    The attached photographs show:
    1.The head gasket on the block between cylinders four and six
    2.The inner head bolt location between cylinders four and six
    3.The inner head bolt from between cylinders four and six
    4.The block in the location of cylinder/piston six showing head bolt location between cylinders four and six with gasket removed

    The block has had "top hat" cylinder liners installed about ten years ago and there is no damage to the head or the block due to the action of the combustion gases.

    My query, which I trust someone can answer is how did the combustion gas get into the coolant as there are no coolant passages between the head and the block in the central area of the head. From what I have read elsewhere the installation of the "top hat" liners should remove the likelihood of combustion gas entering the coolant chamber through small cracks in the block around the liners.

    1. Head gasket on block between cylinders four and six
    P38 burnt out head gasket-img_2724.jpgWhile the gasket has burnt out from both cylinders 4 and 6 into the upper hole for the head bolt the gasket "fire ring' in the vicinity of the lower/outer bolt hole shows signs of future burn through from cylinder 6

    2. The inner head bolt location between cylinders four and six
    P38 burnt out head gasket-img_2725.jpg

    3. The inner head bolt location between cylinders four and six
    P38 burnt out head gasket-img_2726.jpg

    4. The block in the location of cylinder/piston six showing head bolt location between cylinders four and six with gasket removed
    P38 burnt out head gasket-img_2728.jpg

    Any comments/solutions would be greatly appreciated.

    - Darryl

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  3. #2
    FRESHMAN ROVER
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    Re: P38 burnt out head gasket

    Check if liners haven't dropped, I had this happening with mine, also top hats.

    Now this is probably over the top, but if there is a lot of blow by between the cylinder, check surface of heads and block, have it planed if needed.

    Your working with aluminium, MAKE SURE THERE'S NO OIL LEFT IN THE TREADED HOLES!!! Blow it out with an air gun, preferably clean afterwards with brake cleaner and blow out again.

    You need new head bolts, these are stretchers. Now, the official way is 20Nm 90 degrees and another 90 degrees, this is thight!! You can do 40Nm and than 100Nm if you don't trust angle.

    Get yourself a tap with the treat of the head bolts, retap the treaded hole where the stuffed bolt comes out, and check it with a fresh bolt and look into it with a torch.

  4. #3
    FRESHMAN ROVER
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    Re: P38 burnt out head gasket

    Any idea what kind of pistons went in?

    When I had my liners put in I needed new pistons anyway, so I put HC 4.0 liter pistons in.
    Aussie Land Rovers all have low compression. (stock Aussie 8.13:1 - HC 9.35:1)

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  6. #4
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    Re: P38 burnt out head gasket

    have a machine shop check your cylinder heads for warpage, resurface as needed. this is a sign that something failed to seal could have been a warped head leading to improper gasket seating and sealing, improper tight bolt due left over fluids in during assembly causing bolt hydrolock thus leading to false torque readings, simply loose or improperly tight bolt during assembly.
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  7. #5
    Moderator RRToadHall's Avatar
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    Re: P38 burnt out head gasket

    improper torquing of stretch bolts can easily cause that issue. Change over to head studs it is the only way to gain proper torque
    "The power of good is always stronger than the power of non-good.
    The power of light is stronger than the power of darkness,
    the power of knowledge is stronger than the power of ignorance."
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  8. #6
    JUNIOR ROVER
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    Re: P38 burnt out head gasket

    You will always get a little pressurisation due to thermal expansion. If you take the header cap off when the engine is hot, it will be there, if you wait until it has cooled down, it shouldn't be. However, with the head gasket in that state some combustion gases could easily get down around the outside of the top hat liner anyway. As said, that was caused by those two head bolts not being tight enough, maybe due to a hydraulic lock, maybe they weren't torqued down properly or simply that you had weak stretch bolts. The other possibility is that the liners were changed following a problem that almost certainly resulted in an overheat and the threads in the block were weakened then. Helicoil inserts will need to be fitted if that is the case. Personally I have never fitted stretch bolts after taking heads off, I will always change to studs, far easier to torque down and no variations in pressure due to differing stretch on the bolts (and looking at the picture of the bolt I suspect it was overstretched anyway rather than the bit missing being due to erosion from the combustion).

    The head will need to be skimmed as the alloy will almost certainly have eroded and the top of the block will need to be cleaned thoroughly and checked for any erosion there too.
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  9. #7
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    Re: P38 burnt out head gasket

    Have a little experience in the steam arena, I have found that it is easy to mistake a small pressure relief for a small vacuum relief. The cap has a pressure relief if the system gets too pressurised during use, something we are all used to. In addition it has a vacuum relief in order to relieve any vacuum in the system when cold. The vacuum relief isn't "set to" zero, but needs to be a little below zero before opening.

    If the system has been hot (normal use) and the next morning is cool, it is possible for a slight vacuum to be created through the condensation of water vapour. This will manifest itself as a slight noise when removing the cap which sounds like a pressure relief.

    Just another thing to ponder

  10. #8
    DJB
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    Re: P38 burnt out head gasket

    Thank you Reinhoud, I will doubly check the threads as suggested and tap if necessary. After further research and discussions with an engine reconditionor I intend to install studs when I rebuild the engine. I also intend to have the heads skimmed.

    Regards,
    Darryl

  11. #9
    DJB
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    Re: P38 burnt out head gasket

    After further research and discussions with an engine reconditionor, as per your recommendation I intend to install studs during the rebuild, along with a skim of the heads.

    Thank you for your interest and comment.

    Regards,

    Darryl

  12. #10
    DJB
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    Re: P38 burnt out head gasket

    Richard,

    Thanks for your interest and reply. I intend to install studs and skim the heads as recommended.

    Regards,

    Darryl

  13. #11
    DJB
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    Re: P38 burnt out head gasket

    Dtoyne,

    Thank you for your comments. I always checked the coolant level in the morning when the engine was cold immediately before starting and always had the short "pff" sound and could never establish whether it was a pressure relief or a vacuum suck.

    I will certainly ponder it a bit more once I have the engine up and running.

    Regards,

    Darryl

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