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Thread: Radiator Recovery/Expansion Tank - Need Info

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    FJ20DEBT NISMOgemini's Avatar
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    Radiator Recovery/Expansion Tank - Need Info

    Few quick questions on Recovery/Expansion Tank that im about to get made up.

    (Note i have the pressure cap on the radiator and want to keep it here. i do not want to move this cap to the recovery tank if i can avoid it. I plan to have a recovery tank with just a standard spin on filler cap to fill/bleed the system/check on fluid level in the tank)

    1- the hose between the coolant system and the recovery tank. Before or after the thermostat? (or makes no difference?)
    2- should the tank have a breather hole? or does it need to stay pressurized as part of the whole cooling system? (system over flow though the pressure cap on the radiator only?)
    2 - connecting hose size? i was planning on 1/2inch?
    3- what volume should i allow for? FJ20 Turbo, was planning on 1L filled 1/3rd at running temp

    cheers
    Gene
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    Registered User 9triton's Avatar
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    as you want the pressure retaining to be at the rad cap - needs vent hole (or overflow tube) in tank- it runs at atmospheric pressure - which is why you see those aftermarket nylon tanks with flip top lids -don't need to retain pressure

    do you have a 'recovery 'rad cap on the rad ?-wont work without one

    hose to tank from highest point - which is generally the overflow spigot on the rad neck otherwise you wont get the air out of system

    they work by siphoning back into the rad - thus the tube inside the tank needs to be extended to bottom of the tank (if top entry) -or bottom entry tube ( ooh err) and doesn't need large diameter rubber hose to the overflow bottle . I reckon 5/16" would be fine

    a quick google and :

    Last edited by 9triton; 28-11-17 at 11:10 AM.

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    FJ20DEBT NISMOgemini's Avatar
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    ^^ this sounds like a non pressurized system.
    I think by keeping the cap on the rad id be running a pressurized system? and therefore i dont need a recovery cap.?
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    Quote Originally Posted by NISMOgemini View Post
    ^^ this sounds like a non pressurized system.
    I think by keeping the cap on the rad id be running a pressurized system? and therefore i dont need a recovery cap.?
    All coolant systems are pressurised.

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    Registered User 9triton's Avatar
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    -look at the diagram - if you don't run a recovery cap (which is also a pressure retaining cap)- how is the coolant gonna get back to the radiator from the atmospheric tank?
    a recovery cap is essentially two way valve- lets the pressure (and trapped air) out as engine gets hot and coolant expands past 13- 16 psi . then seals again as pressure is relived at t 13 - 16 psi -whatever .
    then as engine cools when switched off and pressure in rad drops it has a small valve in centre that opens and allows the rad to suck back in the coolant - but it needs to be fulley sealed to allow the suction to syphon back the coolant - hence the extra rubber ring on a recovery cap (and second valve)


    std non recovery cap on left

    recovery - with extra rubber seal for rad filler neck on right

    Last edited by 9triton; 28-11-17 at 11:27 AM.

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    Goat roper Motherfucker Jones's Avatar
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    just to clarify; you want to run an expansion tank as part of the pressurised system, like a lot of modern cars, not a recovery/overflow tank which is regulated by the radiator cap and is not pressurised?

    Most of the cars I've seen with expansion tanks run a 1/2" to 3/4" hose that basically feeds of the bottom radiator hose, so on the suction side of the water pump.

    The tank would need to be sealed or otherwise you will have no pressure in the cooling system
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    Registered User 9triton's Avatar
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    Op post said he wants a tank to 'fill / bleed /check the level '

    s o need a clarification as to want really wants
    Last edited by 9triton; 28-11-17 at 11:41 AM.

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    buy OEM. Mazda 3, dualis, or many others.

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    FJ20DEBT NISMOgemini's Avatar
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    Hold up, will draw a picture....

    9triton, the tank would have a cap just to put fluid into the system with. you can assume its no there at all
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    FJ20DEBT NISMOgemini's Avatar
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    This is what i was planning?
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  11. #11
    FJ20DEBT NISMOgemini's Avatar
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    Quote Originally Posted by tim510 View Post
    buy OEM. Mazda 3, dualis, or many others.
    not enough shiny
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    FJ20DEBT NISMOgemini's Avatar
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    Quote Originally Posted by Motherfucker Jones View Post
    just to clarify; you want to run an expansion tank as part of the pressurised system, like a lot of modern cars, not a recovery/overflow tank which is regulated by the radiator cap and is not pressurised?

    Most of the cars I've seen with expansion tanks run a 1/2" to 3/4" hose that basically feeds of the bottom radiator hose, so on the suction side of the water pump.

    The tank would need to be sealed or otherwise you will have no pressure in the cooling system
    yes sorry, thats correct, expansion tank


    Pros vs cons of expansion vs recovery?
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    Quote Originally Posted by NISMOgemini View Post
    This is what i was planning?
    That will not work as the cooling system won't be pressurised. Like I said all cooling systems are pressurised this is to stop the coolant boiling.

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    Registered User 9triton's Avatar
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    maybe it a generic naming problem :

    at the end of the day - both tanks (recovery/ expansion)are there for expansion of the coolant.

    coolant expansion is what build the pressure in the cooling system.

    a' recovery 'expansion tank allows coolant flow back to the rad to keep it full - whilst being non pressurised.

    an 'expansion tank when plumbed to the bottom of the rad will allow the water to expand into the tank - will be a pressuirsed tank at the coolant sytem pressure.- but should have the top connected to the pressure relief -ie rad cap to allow expansion into it-and relif out top .
    Last edited by 9triton; 28-11-17 at 12:57 PM.

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    Registered User 9triton's Avatar
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    just look what an FJ20 system would have and do that ..

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    Quote Originally Posted by NISMOgemini View Post
    This is what i was planning?
    Won't work. Expansion tank needs to be connected to radiator overflow pipe at radiator cap. Recovery type cap used. Edit: unless the cap you are putting on seals 100%. Still a pointless excercise.
    Last edited by BigJonWB; 28-11-17 at 12:32 PM.

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    Quote Originally Posted by NISMOgemini View Post
    This is what i was planning?
    Problem with that is your top tank is hydraulically locked, fluid isn뭪 going to enter or exit


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    FJ20DEBT NISMOgemini's Avatar
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    the pic above is exactly the same as my last vehicle. except the radiator cap was on the tank and no cap in the radiator at all.



    so i want to do it like this? (attachment) is the pindick hose from under the cap large enough to move enough fluid back and forth?
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    FJ20DEBT NISMOgemini's Avatar
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    in that one above im assuming the tank will need an overflow
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    Quote Originally Posted by NISMOgemini View Post
    in that one above im assuming the tank will need an overflow
    Yea but you only get the tank overflowing when you boil the coolant.

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    FJ20DEBT NISMOgemini's Avatar
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    just to confrim

    so the 2 are connected only by the small line under the radiator cap. (i woudl have thought the line would have needed to be bigger ID?)
    the tank will have an over flow at the top, but not via a pressure cap.

    will the radiator need a specific recovery style cap? or they are all the same same?
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    Registered User 9triton's Avatar
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    the tank- is a 'dead end' and has no fluid flowing thru it (unlike a radiator)

    working range (low level to upper level ) for the recovery(expansion tank ) is probably half a litre.

    this is from stone cold to operating temp. in say 5 minutes ?

    so you are pushing half a litre thru a hose in 5 mins at 16 psi

    = yes a small diameter 5/16 hose will do it.- which conveniently is usually approx. the rad over flow spigot size

    also for the syphon back to the rad when it cools a small diameter hose is best.

    return journey as it cools is over say 40 mins - so even less flow a minute
    Last edited by 9triton; 28-11-17 at 02:59 PM.

  23. #23
    Half Shafted. Madhatr's Avatar
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    expansion tank = pressurised.
    overflow = not.

    Normally cars these days have the expansion tank connected to the heater hose return from the core, so I would be looking at a minimum 5/8 size. The smaller lines are normally there to help bleeding from a high spot in the system, not to supply everything with coolant. Smaller hoses are usually vent lines from high spots in the system and returns into the expansion tank above the fluid line. Expansion/contraction is largely done in the expansion tank itself, thats why tanks these days have a specific level you shouldn't fill above. It's to leave room for the vent to pressurise the system without damaging the expansion tank. They aren't really designed to vent/discharge to atmosphere at all, it's really supposed to be contained within the expansion tank.

    what exactly is the problem with not having a filler on the radiator?
    Last edited by Madhatr; 28-11-17 at 04:55 PM.
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    FJ20DEBT NISMOgemini's Avatar
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    Madhatr - I was hoping to go expansion tank, but its looking easier with my current set up to go with recovery. (radiator is already fabricated)
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    Registered User dnegative's Avatar
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    Quote Originally Posted by NISMOgemini View Post
    the pic above is exactly the same as my last vehicle. except the radiator cap was on the tank and no cap in the radiator at all.



    so i want to do it like this? (attachment) is the pindick hose from under the cap large enough to move enough fluid back and forth?

    Swap caps and your good though I would recommend running a bigger feed, OEM's normally run a reasonable sized hose (and generally a bleed line off the head with a restrictor) to the bottom hose;
    But it would probably work alright if you screwed a 1/4" ID fitting into the filler neck.

    Header tanks are still designed to vent (cap wise) even with the air volume they are designed with but only when things go tits up and or they have recovery tanks built in - they are really nice for knowing an honest true coolant level and make integrating level sensors easy but there isnt one made of plastic that doesnt fail with age.
    Aluminium or stainless one with a glass level would be ideal.
    Last edited by dnegative; 28-11-17 at 07:39 PM.
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    Half Shafted. Madhatr's Avatar
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    To simplify it all, id still probably weld a bung in the filler neck of a radiator and just seal it off permanently to avoid having to bother about it ever again, but as said above, a single stage cap in the radiator and use the expansion tank as the dual, and just bleed and refill from the expansion tank. Especially if the tank is located higher than the radiator.

    I know they can vent, what im saying is they really arent designed to vent. Neither is the system. It's designed to be able to contain the expansion and contraction of the coolant during use without losing any of the coolant. They pretty much just have a vent in it to save shit from exploding when it all goes to shit like you said.

    I've been through this with the E46, trying to find something metal that you can incorporate a level sensor into as I reckon it's stupid not to have a warning the level has dropped. Made even harder these days because a lot of level sensors are magnetic based and sealed off from the tank these days to avoid any potential sources of leaks.

    Im going to try making neck for an early factory bmw level switch to sit into so I can fit it into a alloy tank if i make a neck and cut a matching thread on the lathe. Plastic isn't AS bad if you can keep it away from direct heat sources, but its still a failure/replacement item any time anything else in your cooling system shows signs of age/heat. Bmw (in their wisdom) put the fuckers right on the back of the radiator and wedge it between the radiator and motor.
    Last edited by Madhatr; 28-11-17 at 08:09 PM.
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    FJ20DEBT NISMOgemini's Avatar
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    Quote Originally Posted by Madhatr View Post
    To simplify it all, id still probably weld a bung in the filler neck of a radiator and just seal it off permanently to avoid having to bother about it ever again, but as said above, a single stage cap in the radiator and use the expansion tank as the dual, and just bleed and refill from the expansion tank. Especially if the tank is located higher than the radiator.
    This would then expand (fill and empty) via a line in the bottom of the radiator as apposed to the top?

    no issue having the cap on rad and the tank?
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    Registered User dnegative's Avatar
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    Its just a matter of spending some time at a euro wrecker seeing what you can make fit;
    I do prefer header tanks, its just easier to see level/condition and run an alarm if you get a tank that has one built in.
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  29. #29
    Registered User dnegative's Avatar
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    Quote Originally Posted by NISMOgemini View Post
    This would then expand (fill and empty) via a line in the bottom of the radiator as apposed to the top?
    If your going to have it connected to the bottom you want an air bleed from the highest point, restricted, otherwise you will have an air lock in the top tank and you will struggle to 1/2 fill the system.
    Last edited by dnegative; 28-11-17 at 08:45 PM.
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    Registered User matty12's Avatar
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    If you want to use what you already have you could use a blanking cap on the radiator and then fit what i call a header tank this will be pressurised. It would be alittle small being a 5/16 fitting, most cars using a header tankbwith a main feed use 5/8 or 3/4 hose generally before the water pump. An overflow or expansion tank takes exactly that, the overlfow or expansion of the system as it heats up.

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