coolant overflow tank not working?

Discussion in 'Technical' started by J3bba, Sep 27, 2017.

  1. J3bba

    J3bba He Who Struggles

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    Hey all,

    So I'm not sure my coolant overflow is working properly. The radiator doesn't seem to be topping itself up from the overflow tank. It works on the way out as the overflow tank gets more in it but then when I open up the radiator it seems to be down a bit on coolant. The overflow tank seems to be in good nick and there aren't any leaks in the coolant system.

    I have a larger aftermarket aluminium radiator which came with a cap that I'm using if that makes a difference.
     
  2. Fists

    Fists Well-Known Member

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    Probably drawing air instead of water some where, check the upper seal on the cap and the face it seals on are good, check the nipple for the overflow hose is sealed into the neck properly (air tight) and the hose is fitted to the nipple and the tank and doesn't have any pin holes in it.

    Also check the return valve in the cap moves freely, little metal bit in the centre bottom of the cap should be able to be pulled down as that's how the water returns.
     
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  3. MAX

    MAX Ex Zedder

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    Could also be air in the system. Generally the water shouldn't move out or into the radiator if the system is working well.
     
  4. QLDZDR

    QLDZDR ID=David

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    Radiator cap?
     
  5. J3bba

    J3bba He Who Struggles

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    Fluid seem to be moving out of the system as there's more coolant in the overflow than when I filled it up after the last flush. I just assumed it was the coolant expanding as it got hot, but then it doesn't seem to be getting sucked back in as it cools down again.

    I actually just looked at the cap and compared it to the stock one I have and it has 1.3 stamped on it (I assume that's the pressure rating) while the stock has 1.2. That would probably make a difference wouldn't it?
     
  6. MagicMike

    MagicMike Moderator Staff Member

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    Chances are you have a slight pressure leak somewhere. Not enough that it doesn't flow into the overflow, but enough to let air back in instead of the coolant returning to the rad.

    Check all the things fists has said above. Start with swapping rad cap.
     
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  7. Fists

    Fists Well-Known Member

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    Not sure if we're mis-reading Max's comment but there definitely should be some movement in and out of the overflow as the car is heat-cycled, a functioning air-tight overflow system is absolutely essential in these cars to keep the radiator bled and head gaskets in good order.

    Pretty small difference, raises the boiling point a little but also puts a little more stress on the coolant hoses. If fitting a lower pressure cap helps either the cap was damaged or there's a dodgy hose connection somewhere leaking a tiny bit.
     
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  8. MAX

    MAX Ex Zedder

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    If all your house are working then it will be air in the system. An air bubble will heat and cool very quickly compared to water. It will also expand and contract much more that water. When it expands it can force fluid out the cap. But if the air is not also purged past the cap and it's still trapped in the system, when the car cools rather than sucking water the air bubble contracts leaving the water In the overflow.

    Do you know how to bleed the system? Because in my opinion this is easier to check first rather than trying to check everything else first.
     
  9. J3bba

    J3bba He Who Struggles

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    Yeah, bled the system when I did the change. Probably didn't get all of it out though.
     
  10. MAX

    MAX Ex Zedder

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    Ran the heater on and off a few times and ac and of a few times with the rad cap off?
     
  11. J3bba

    J3bba He Who Struggles

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    Yeah, but you can never get it all out. There are way too many random coolant lines.


    I've switched the cap over to the stock one and topped it up so we'll see if it makes any difference.
     
  12. MAX

    MAX Ex Zedder

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    Also check the overflow from the overflow is not blocked. This will cause a vacuum in the tank when chilling down and make it harder to suck the water back.
     
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  13. MickW

    MickW Carntry member...

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    Location:
    Bendigo, central VIC
    Reinforcing what others have already said about air leaks or blockages in the overflow tube -
    I had the same problem once. The OEM rubber pipe that goes on the radiator filler neck's overflow nipple
    was perished. It was loose on the nipple so I cut a bit off it and that made it a snug fit onto the nipple.
    But that hose was also perished and cracking several inches lower where I couldn't see it.
    Not cracked bad enough to leak expelled coolant and leave a telltale sign, the affected area was in a vertical section,
    but bad enough to let air in while the radiator was trying to recover coolant. New generic hose, solved.

    Blockages - I once worked on another dude's Zed where the overflow tank looked cleanish from the outside but
    turned out later there were strange lumps in the bottom of it which we couldn't see.
    When the radiator was trying to recover coolant, these lumps - I THINK - would get
    sucked against the exit hole and block off the outflow. I couldn't actually see that happen so it's an educated guess
    but after I removed the overflow canister and flushed the lumps out the problem went away.

    Fuctifino where those lumps came from, maybe oil from a blown engine 2 owners ago mixed with 20 years of sediment?
     
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