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  1. #1
    Join Date
    Nov 2004
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    Arrow Any reason not to install a header tank?

    I have a Thornycoft 245 with a Bowman heat exchanger. The fresh water filling cap has a 2 inch copper overflow pipe which just vents into the bilge. When I do the weekly check on the coolant level I have no real idea if I'm loosing coolant and I'd want to know that ASAP! All I do is just top up but i dont know whether all i'm doing is overfilling each time, clearly on such a big unit there will be a largish amount of expansion. So I thought I'd add a simple expansion tank to the overflow pipe, is there any reason not to do this? Would it add pressure to the system? Does the expansion tank have to be above, level or below the heat exchanger?

    Thanks for your advice.
    Colvic Watson slideshow video http://www.youtube.com/watch?v=6RayUzX7LZQ

  2. #2
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    Quote Originally Posted by The Lazy Kipper View Post
    I have a Thornycoft 245 with a Bowman heat exchanger. The fresh water filling cap has a 2 inch copper overflow pipe which just vents into the bilge. When I do the weekly check on the coolant level I have no real idea if I'm loosing coolant and I'd want to know that ASAP! All I do is just top up but i dont know whether all i'm doing is overfilling each time, clearly on such a big unit there will be a largish amount of expansion. So I thought I'd add a simple expansion tank to the overflow pipe, is there any reason not to do this? Would it add pressure to the system? Does the expansion tank have to be above, level or below the heat exchanger?

    Thanks for your advice.
    engine coolant will normally get to a natural level, too much & it will spit it out via the l filler cap / over flow pipe.
    if you fit an expansion tank you will have to remove the existing cap & replace with one without the spring, my tank is above the engine height
    I may be wrong but not always

  3. #3
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    If its worked up until now without an expansion tank then it should be ok
    Try a hose from the copper pipe into a plastic bottle to monitor overflow
    Most engines will have a level that they will run happily and if you do overfill then they just push it out so next time dont refill but see what happens.

  4. #4
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    No need to replace the cap as I was going to take it from the overflow pipe. I think one of the attractions of a tank is I can put it in an easy to see place, currently checking the water level means climbing into the engine room. A tank would give an easy visual check when opening to engine room door to change the batteries to engine start.
    Colvic Watson slideshow video http://www.youtube.com/watch?v=6RayUzX7LZQ

  5. #5
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    Quote Originally Posted by The Lazy Kipper View Post
    No need to replace the cap as I was going to take it from the overflow pipe. I think one of the attractions of a tank is I can put it in an easy to see place, currently checking the water level means climbing into the engine room. A tank would give an easy visual check when opening to engine room door to change the batteries to engine start.
    with a header tank the sprung loaded pressure cap goes on that not the engine h/e
    I may be wrong but not always

  6. #6
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    Quote Originally Posted by sailorman View Post
    with a header tank the sprung loaded cap goes on that not the engine h/e
    Are you sure it has to?
    Colvic Watson slideshow video http://www.youtube.com/watch?v=6RayUzX7LZQ

  7. #7
    theoldsalt is offline Registered User
    Location : me Bristol, boat Plymouth
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    The normal purpose of an expansion tank is not only to take excess coolant expelled on expansion but to replace that water in the cooling system when the engine cools down and is normally mounted higher than the engine. Therefore connecting to the overflow pipe without changing the pressure cap will only allow expansion and not contraction on cooling as the valve on the pressure cap closes. All you would be doing is monitor the expelled coolant as Scottie suggests. That tank can be anywhere.

  8. #8
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    Quote Originally Posted by The Lazy Kipper View Post
    Are you sure it has to?

    i installed my engine & stern gear
    I may be wrong but not always

  9. #9
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    Quote Originally Posted by theoldsalt View Post
    The normal purpose of an expansion tank is not only to take excess coolant expelled on expansion but to replace that water in the cooling system when the engine cools down and is normally mounted higher than the engine. Therefore connecting to the overflow pipe without changing the pressure cap will only allow expansion and not contraction on cooling as the valve on the pressure cap closes. All you would be doing is monitor the expelled coolant as Scottie suggests. That tank can be anywhere.
    OK, that explains things. So I just need to put a pipe on the outlet into any old bottle, I know then if I've topped the level up too much and can work out the cold engine level of coolant to go for.
    Colvic Watson slideshow video http://www.youtube.com/watch?v=6RayUzX7LZQ

  10. #10
    theoldsalt is offline Registered User
    Location : me Bristol, boat Plymouth
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    When I first had an engine with a heat exchanger I made the same mistake of filling to the brim only to find water in the bilge and the heat exchanger only half full. I soon realised what was happening. My engine runs happily with the coolant (when cold) just above the tubes in the heat exchanger. Any more coolant added just gets expelled when the engine heats up. I don't have a header tank. I did consider one but was advised it was not needed
    Last edited by theoldsalt; 22-04-12 at 22:56.

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