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  1. #1
    Join Date
    Nov 2004
    Location
    Portsmouth, Hampshire
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    226

    Radiator header cap sizes

    I have been running my engine for longer periods whilst I check things and prepare for my IVA retest.
    I have noticed that as soon as the engine starts to warm up it is spitting out water through the pressure release pipe next to the header cap.
    Having measured the cap and the header I am now wondering if I have the wrong cap as I think there is literally no downward pressure when fitting the cap.
    So my question is, when fitting an old style radiator cap should you feel the seal touching the flange before tightening?
    Also my neck is about 20.4mm high and the radiator cap is almost exactly the same from the face to the seal and about 25mm high in total. Im thinking it should be noticably longer ?
    Paul

    SRV8 - 429 Ford Big Block, 4 speed toploader

  2. #2
    Join Date
    May 2004
    Location
    Finchampstead, Berkshire, UK.
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    54
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    3,566
    Yep, you should need to lean on it to compress the spring (then twist to close).
    GD Mk3 Jag based
    Supercharged LS1
    GD J1M

  3. #3
    Join Date
    Jun 2004
    Location
    Northampton
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    1,555
    I bought two stainless ones, one for the expansion tank and the other for the coolant fill and the latter leaked. Presumably this is because the spring is not compressing sufficiently to produce a seal. Can this be overcome by putting a washer in the fill neck?
    Dek

  4. #4
    Join Date
    Nov 2004
    Location
    Portsmouth, Hampshire
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    226
    Thanks Jim, Having looked on the internet there seem to be two standard options for most old style rad caps, standard or long reach. The standard is pretty much exactly the same length as my neck and the long is about 10mm longer. I guess I try a Long and see. Just dont want to risk a cap that cant let pressure off.

    Dek, I would suggest fitting the right cap, patching up the cooling system with extra washers is probably asking for problems.
    Paul

    SRV8 - 429 Ford Big Block, 4 speed toploader

  5. #5
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,449
    My FE came with a 6ib cap - crap - had exactly the same problem. After a 10 mile drive header tank boiling over and pissing out in the garage.
    A quick look over the pond at ClubCobra demonstrated folks with using 11 and 13lbs, so I went with a 12lb stainless cap.
    Overheating problems cured.

    May be useful:
    https://www.carbuildersolutions.com/...grid&orderBy=0

    https://www.youtube.com/watch?v=OPKaFcOwemI
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  6. #6
    Join Date
    Nov 2004
    Location
    Portsmouth, Hampshire
    Posts
    226
    Been doing a bit more measuring and managed to pick up a rad cap with a long reach...
    The neck is 20mm deep which I guess is 3/4" in old money but seems slightly more . My current radiator cap measures exactly the same extended. I tried a long reach cap I picked up and it fits but when I fully compress the spring it is again 20mm as best I can tell, which worries me because I would assume there should be resonable movement to let the pressure out of the overflow and the neck is 20mm.
    So I am back to the question should the cap sit quite proud of the rim when open or should it just sit right down over the rim making me feel like there is not much of a seal?
    I dont have another old style radiator to compare.

    Alos are people tending to run expansion collector tanks as well as a header tank ? I would have assumed not ?
    Paul

    SRV8 - 429 Ford Big Block, 4 speed toploader

  7. #7
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,449
    i have an expansion tank that is fed from the overflow pipe on the FE header tank - i.e. expansion tank is unpressurised.
    It sits at the bottom of the inner wing, and sits about 1/2 full. If the header tank pukes, it goes down the pipe to the expansion tank until it settles down and then sucks the fluid back.
    At least that's the theory (see video on CBS website in above link) - I am not sure any of it has been needed since i got the 13lb cap fitted.
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  8. #8
    Join Date
    Nov 2004
    Location
    Portsmouth, Hampshire
    Posts
    226
    I have bought a new cap the same as my old one and will see how it goes....IVA retest on Friday !!!
    Paul

    SRV8 - 429 Ford Big Block, 4 speed toploader

  9. #9
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    8,449
    Good luck!
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  10. #10
    Join Date
    Nov 2004
    Location
    Portsmouth, Hampshire
    Posts
    226

    Smile

    Just to close this thread off, I fitted the new cap and it was a little better. Strangely since passing my IVA at 93db with side pipes, it is now running fine and to temperature....I cannot imagine what changed but air is now coming out of my exhausts and my loft is insulated again!
    Paul

    SRV8 - 429 Ford Big Block, 4 speed toploader

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