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  1. #1
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    coolant system holding pressure

    I had a curious problem the other day ,after taking the car out for a run . The next day noticed coolant on the garage floor it had come from the bottom hose so i wiped it and some more came out ,so i checked the hoseclips and they were fine. On further inspection i found that on removal of the pressure cap a popping sound came out so the system had held pressure overnight .I have repeated this cycle several times since and gone for a long drive (50 miles ) and it holds a little pressure which i then release when cool,it just seems a little strange as i have no symptoms of a head gasket failure or anything like that.I wondered if the pressure cap on my expansion cap is incorrect for my application as it rated at 1.3 bar anybody come across this on a ford 302 cheers
    mike

    pilgrim sumo mk3 3.5l rv8 sold

    ak gen 1 ford 302ci otr

  2. #2
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    Jan 2006
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    Hi Mike,

    I would see were the leak is coming from as you say bottom hose but it could be from the radiator core and dripping down looking like its from bottom hose. Core shift of the radiator is common as the core sides move and solder joints crack especially on old copper radiators. Have a closer inspection of the core bottom and side tanks of the rad you might unfortunately see some antifreeze water . The pressure and removal of the cap is normal as you have a vacuum due to expansion of the water.

  3. #3
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    Quote Originally Posted by jon1d View Post
    Hi Mike,

    I would see were the leak is coming from as you say bottom hose but it could be from the radiator core and dripping down looking like its from bottom hose. Core shift of the radiator is common as the core sides move and solder joints crack especially on old copper radiators. Have a closer inspection of the core bottom and side tanks of the rad you might unfortunately see some antifreeze water . The pressure and removal of the cap is normal as you have a vacuum due to expansion of the water.
    hi jon thanks for your reply it was definately seeping from the bottom hose/waterpump joint and i have a new ali rad it just seems a bit weird to still have pressure in the system the morning after when everything has cooled down , ive never come across this before in my other cars but i shall have to keep an eye on it .
    cheers
    mike

    pilgrim sumo mk3 3.5l rv8 sold

    ak gen 1 ford 302ci otr

  4. #4
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    The popping maybe air going back into your circuit, as well as out.

    If it’s leaking water (maybe as it’s hot and under pressure), then there’s a loss in volume. When it cools that will create a vacuum, which could create a pop as you release the cap.

  5. #5
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    Sep 2007
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    Hilperton,Wiltshire
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    I would change the rad cap.


    Andy

  6. #6
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    When cold, how much coolant is in the expansion tank? It could be that the system is overfilled and when the coolant expands there isn't enough room in the tank so the pressure gets too great. 1.3 bar sounds way too high, my Ford 302 runs with a 7lb pressure cap.
    Cheers, Clive

    (If I'm not here, I'm either in my new workshop or on the golf course!)

  7. #7
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    1.3 Bar is almost 19lb which is a little higher than normal. I run a 13psi which is normal cap pressure . You sure it says bar and not 13psi sounds a bit of a coincident. The cap is only there as a relief valve to allow blow out after the pressure is reached. So lowering the the pressure rating would mean you get blow past at a lower pressure that before. If you up the cap pressure rating then the system pressure will go higher and stress your joints. Is the temperature stable on the run and what levels when cool in the expansion tank as over filling the level would again stress the system and end in the radiator cap blow by.

  8. #8
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    Quote Originally Posted by Clive View Post
    When cold, how much coolant is in the expansion tank? It could be that the system is overfilled and when the coolant expands there isn't enough room in the tank so the pressure gets too great. 1.3 bar sounds way too high, my Ford 302 runs with a 7lb pressure cap.
    thanks clive it is about one third full when cold i'll change the cap to see if it cures it.
    cheers
    mike

    pilgrim sumo mk3 3.5l rv8 sold

    ak gen 1 ford 302ci otr

  9. #9
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    Just out of interest I removed my rad cap just now, it hasn’t run for a couple of days.....it also went “Pfst” as I removed the cap
    GD Mk3 Jag based
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  10. #10
    Join Date
    Jul 2012
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    NW England
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    Quote Originally Posted by Happy Jim View Post
    .....it also went “Pfst” as I removed the cap

    Perhaps it was trying to get your attention!

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