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Thread: radiator expansion tank : height question

  1. #1
    apriliaforum Junkie groovymaster's Avatar
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    radiator expansion tank : height question

    Where does a radiator expansion tank need to be positioned?

    It's a pressurized system and the expansion tank is also the fill location for the system via a pressure-release cap. That is, the both the radiator and tank are pressurized and thus the tank does not gravity feed.

    QUESTION: On the expansion tank, does both the inlet and bottom outlet need to be higher than the radiator [A] or does only the inlet need to be higher [B] than the radiator?
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  2. #2
    apriliaforum expert Fox Fader's Avatar
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    The inlet and outlet are the same line. The other line is suppose to be a dump in case the overflow tank fills. It doesn't matter if it's higher or lower, once pressure expands the fluid into the tank it will contract back in when it cools, as long as there is enough extra coolant in the overflow tank.
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  3. #3
    apriliaforum Junkie groovymaster's Avatar
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    Quote Originally Posted by Fox Fader View Post
    It doesn't matter if it's higher or lower
    This would be sweet.
    It sure would make my life easier if it didn't matter whether
    the expansion tank was attached hi/low relative to the radiator.

    However, I'm not sure we are talking about the same thing.

    • It doesn't matter whether the expansion tank is positioned higher or lower? The fill opening is on the expansion tank not the radiator. I would assume that the fill opening MUST be positioned as the highest point in system. Is this incorrect?

    To be clear, my radiator has an expansion tank not an overflow tank. The radiator does not have a fill opening; instead, the expansion tank has the fill opening with a pressure-release cap. An expansion tank is part of the pressurized system. An overflow tank is not. A radiator with an overflow tank has the fill opening and pressure-release cap on the radiator; it allows fluid to be dumped into a non-pressurized external tank.

    .
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    Last edited by groovymaster; 03-17-2010 at 11:11 PM.

  4. #4
    apriliaforum expert Fox Fader's Avatar
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    It doesn't have to be higher, BUT if it's too low, it will make an initial fill more work. You'd have to fill it as far as gravity will let you if it's lower, then let it warm, expand, then add more fluid.
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  5. #5
    apriliaforum expert williamr's Avatar
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    If it's too low, when you release the cap coolant in the radiator above the level of the filler will flow down and into the expansion tank - but very slowly as air needs to get in along the same path as coolant is using to get out. This is likely to allow enough air into the system to potentially cause an airlock at some point. You need the filler at the highest point in the system.

    I think - and feel free to argue - that the bottom of the expansion tank should be higher than the bottom of the radiator, but doesn't need to be higher than the top of the radiator.

    Pressurised or not, air will always try to get to the highest point in the system.

    Rob

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