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Thread: Radiator caps.

  1. #11
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    NAR rebuilt my FE header tank - nice folks

  2. #12
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    Quote Originally Posted by ChrisP View Post
    I've had my micrometer out this morning (!)

    All my caps are 77mm wide, that's the measurement across the little ears referred to in the Malpas listings. For information, although not quoted anywhere, the internal size of the top is 56mm. The cap that fits my car is the 28mm one (S.41517 in the Malpas list). I've seen this referred to as standard! In which case there are a lot of non standard ones that don't seal! The 28mm is measured from the bottom of the rubber washer to the top of the cap. Interestingly, the one that came with my header tank has a rubber washer on the underside of the cap - not all of them do, a lot have just metal. if you want to check your radiator/header tank my header tank has a 20mm recess measured from the top of the filler cap to the seat. So a 20mm recess with a 28mm cap is my set up. As the cap came with the tank I think we can assume that's right! Incidentally, it's a Champion cap and is 0.9 bar (or 13psi) but a 10 psi would probably be OK. I guess if you can get the fit then the pressure is the final stage.

    For the cost, assuming you have a 20mm or close to it recess, is it worth buying the 28mm and the 29mm from Malpas to establish the fit? Although my money is on the 28mm (standard, haha) working!
    Thanks a lot Chris for getting your micrometer out and explaining what the relevant measurements are. I’ll have to get mine out now! I noticed also there was no rubber seal on the underside of the cap on this one. Thanks again for going to the trouble. Appreciate it. All the best.
    Dek

  3. #13
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    Quote Originally Posted by jon1d View Post
    Dek,

    To stand a chance you need a few dimensions. I guess there is no part no. on the Stant cap. Also a 16lb might do as its close enough. I know my cap is a standard old Ford cap 13lb as the expansion tank is a Ford part.
    You might have to work from the neck rather than the cap. The 26mm reach are also stated as 25mm as its a +- 2mm.

    Cap measurements required.
    1. Rubber upper face too lower rubber face varies for short 22mm to long 26mm.
    2. Rubber lower seal size to seal off the hole.
    3. Top cap size. measure the neck dia of the housing.

    There is a company which might be worth a visit
    https://www.nargroup.com/contact-us/

    Nothing like dropping into a place who know there stuff. That is if they are seeing customers face to face.
    Thanks John for the the explanation of what measurements are needed which fits in with Chris’s. Thanks also for your suggestion of NAR. Why does everyone else know what’s on my doorstep but me?!
    Dek

  4. #14
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    Quote Originally Posted by aaronjb View Post
    NAR rebuilt my FE header tank - nice folks
    Good to know Aaron. Be worth a visit armed now with some measurements and the old cap.
    Dek

  5. #15
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    Quote Originally Posted by Dek View Post
    I noticed also there was no rubber seal on the underside of the cap on this one.
    Dek
    I suspect the didn't have the upper seal where no expansion tank was used, not required to seal against low presure to draw coolant back if there's nowhere to draw it from.

  6. #16
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    Quote Originally Posted by GDCobra View Post
    I suspect the didn't have the upper seal where no expansion tank was used, not required to seal against low presure to draw coolant back if there's nowhere to draw it from.
    Well there is an over-flow (expansion) tank, not header tank so perhaps it should have a top seal.
    Dek

  7. #17
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    Quote Originally Posted by Dek View Post
    Well there is an over-flow (expansion) tank, not header tank so perhaps it should have a top seal.
    Dek
    Either way it's best to have the top seal (better to have and not need than need and not have IMO) but really needed where a header is used to allow the low pressure caused by the coolant, er, cooling to draw the expelled fluid back into the system, otherwise air could be drawn back instead which would kind of defeat the object of having the expansion tank. Worse still if you then filled the system to replace that air more coolant would be pushed into the expansion tank on the next heat cycle and could overflow.

  8. #18
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    Well went to NAR today after a phone call to establish they were open to visitors and met the very helpful Robert who simplified things by saying there were two types of rad cap like mine, short and long. Mine was the longer. He pointed out the importance of not having too high a pressure value so went out and gave me a 10 and 15lb. He didn’t want me to pay just to go away and test them both on the car to see which is best and return the one I didn’t want. He also pointed out leaks could be due to the filler neck which they could manufacture. Mine is ali in the top hose.
    So to help me understand the effects of coolant and pressure on the boiling point of water I did some research and came up with:
    A 50/50 mix of water and ethylene glycol will increase the boiling point to 106C, 223F.
    The boiling point goes up -16.1C, 3F for every pound of pressure.
    So a 10lb cap will increase the boiling point to 116C, 242F.
    And a 15lb cap will increase the boiling point to 125C, 257F.

    Adding the effect of 50/50 ethylene glycol produces:
    10lb cap 122C, 253F.
    15lb cap 131C, 268F.

    Sorry for adding the Fahrenheit values but I’ve got a temperature gauge in F. I had to remind myself what the boiling point of water is in Fahrenheit! -212.

    So would anyone like to corroborate these values and theory? I’ve deliberately ignored the effect on freezing points.
    Tomorrow I’ll put the 10lb cap on first and watch the temperature followed by the 15lb. I’ve got an infra-red thermometer which I’ll also check against.

    Dek

  9. #19
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    It's great to fined a very helpful supplier who knows there business and will to help with there knowledge.
    It sounds like you had a entertaining time.
    Interesting to see how you get on with the two different caps.

  10. #20
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    If Robert is the fella I'm thinking of .. he could talk the hind legs off a donkey. If you put him and Dave B in a room together you'd never see them again

    Good to hear they are still helpful! I think they like a bit of variety that isn't their every day fare

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