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  1. #1
    FEP Member 5pointoh's Avatar
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    Default maintaining the right amount of coolant level

    For my 82 GT which has 5 liter crate motor in it I am just wondering what is the right amount of coolant that should be maintained in the radiator and the expansion tank? From what I know is it between 2.5 to 4 inches below the rad cap seal for the radiator? Also just confirming the reservoir never needs to be filled up? Is this correct?
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  2. #2
    Moderator wraithracing's Avatar
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    I have never heard of any measurement from the radiator cap in my experience, but that doesn't mean anything.

    Generally when refilling and burping the cooling system. I will put the front end up on stands to raise the radiator cap as high as possible. Fill the radiator to just below the cap opening. Then run the car until it comes completely up to to temperature and the thermostat opens, coolant circulating, and the cap off to allow the system to burp/purge any trapped air. I also run the heater core on full high temp to make sure that is purged too. Once the thermostat is open and the system appears to have burped all the air out, I top off the radiator to just below the overflow tube. Install the radiator cap and then I add coolant to the overflow tank to about 1/2 full or so. Then I test drive the car for 20-30 minutes to make sure it doesn't overheat or any other issues. Then I park it and allow to cool down completely. Then I double check the overflow tank. If the tank level has dropped that means the system purged more air and sucked in more coolant. I will add coolant back into the overflow tank to the correct level and then continue to check it every time before driving it for the next few times until the coolant level remains steady. Hope that helps.
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  3. #3
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    Prior to captive overflow tanks, the radiator needed to be filled to a certain height BELOW the radiator cap level. I have not owned too many early Fox bodies so I forget when the full level changed to the overflow tank/bottle. Now that I think of it, my 85 5.0 cfi is the old style. Some time between 1970 and likely 1979, Ford added an overflow tank to catch any spill over. These early one just have a hose stuck into a tank. Later 86-93 5.0, 83-93 EFI, and maybe some others used a hose which attached to a fitting on the tank. All of these with a fitting used a fill level at the tank. Those with a free hanging hose or a hose stuck into a tank use a fill leve at the radiator (below the cap). They often had a label near the radiator cap.

    There were some after market overflow tanks which functioned the same as the early Ford overflow tanks.
    Typically, the fill level at the radiator is about 1” below the neck but it should always cover the radiator fins on a Top tank style. Most Fox body use a side tank style.
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  4. #4

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    Most people I know fill the rad and overflow tank and let the car spit out what it doesn’t need.

    Not good for the environment but has worked for many cars


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  5. #5
    FEP Senior Member BMW Rider's Avatar
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    The radiator should be completely full. The expansion tank should have enough coolant to ensure the radiator stays full when cold and enough room to contain the extra coolant as it expands when at full operating temperature. Some vehicles actually had indicator marks on the expansion tank to show the correct range, but generally around half full cold is fine. If it is too full it will just end up spilling out when hot.

    On a fresh refill of the rad it is almost impossible to get it totally topped off so there will be a bit of air space in there. I usually add a bit extra to the expansion tank and after a couple of hot to cold cycles on the engine, the rad will have expelled the air and drawn back in the coolant.

  6. #6
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    Quote Originally Posted by BMW Rider View Post
    The radiator should be completely full. The expansion tank should have enough coolant to ensure the radiator stays full when cold and enough room to contain the extra coolant as it expands when at full operating temperature. Some vehicles actually had indicator marks on the expansion tank to show the correct range, but generally around half full cold is fine. If it is too full it will just end up spilling out when hot.

    On a fresh refill of the rad it is almost impossible to get it totally topped off so there will be a bit of air space in there. I usually add a bit extra to the expansion tank and after a couple of hot to cold cycles on the engine, the rad will have expelled the air and drawn back in the coolant.
    This line of thought only applies to 86-93 cars. It seems people have forgotten how to fill the 79-85 radiators. Go read the manual!
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  7. #7
    FEP Member 5pointoh's Avatar
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    Default

    Thanks for the tips guys. From what I have seen and read somewhere the expansion tank should be empty and the coolant level should be 2.5 to 4 inches below the cap seal. This seems kind of low but perhaps that is all is needed? Yes, for many other cars there is coolant in the expansion tank and there may be a min/max. However for the 79 to 85 cars it appears to be a bit different as KevinK has pointed out.
    Current Mustangs:
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    05 Legend Lime Fastback - some mods
    05 Screaming Yellow Vert - even more mods including Edelbrock blower

  8. #8
    FEP Senior Member BMW Rider's Avatar
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    No matter the years, the tube goes into the tank down to near the bottom. End result is the same, coolant is drawn back into the rad as it cools and contracts. So unless you start out with the tank empty, you will end up drawing that coolant back into the rad. It is better to have the rad full than low so long as the expansion does not exceed the capacity of the tank which will make a mess. Too little coolant and you will not get optimal cooling and possibly even not enough pressure generation in the system which will reduce the boiling temperature of the coolant. Don't over think it, just fill it up and it will find its own happy place.

  9. #9
    FEP Senior Member Greywolf's Avatar
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    The first time I fill the coolant up after flush/drain, I put a piece of masking tape on the reservoir and use it to mark where I fill the coolant to.
    I fill the radiator as much as I can, burp the hoses, etc, run the engine with the cap off and heater on (cars without A/C may not have a heater valve, but I turn it on full blast anyway). If you can point the nose up to get air bubbles to the radiator (ramps or a hill), even better.
    I then fill the overflow about 1/4 full, making sure that the level is at least a couple inches over the overflow tube. On the tiny '80s Ford overflows, that's more like 1/2 full.
    That's when I mark the masking tape the first time.
    Take the car on a good drive, enough to get it to temperature, mark the level again, then let it cool until it's cool. Don't remove the cap.
    Once it's cold, look at the overflow. If the car is running properly and the end of the overflow tube is submerged in coolant, peel off the masking tape, adjust to the "full cold" mark and you're done.
    If the overflow is empty or the end of the overflow is sucking air, remove the cap, add coolant at the tank and overflow, and repeat.

  10. #10

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    My car enjoys a steamy snack of coolant every time I use the blown heater core to warm my feet. At least until I bring myself to change the heater core

  11. #11
    FEP Super Member erratic50's Avatar
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    With the car sitting on a floor jack at the K member that’s as high as it will go, I usually put the heat on high and fill my overflow about 1/2 way and attach the tube then take off the cap and bring mine up to temp. Once the thermostat opens i bring the rpm up to around 2000-2500 and fill the radiator up the rest of the way while the level is sucked down and cap it.

    I’ve had trapped air and overheating before even with this procedure. Recently I’ve had to purge air at the EGR spacer by the throttle body and at the temp sending unit. For whatever reason my sons convertible was the queen of antichrists and I had to switch over to a 94+ thermostat housing which has a fan temp sensor bung right at the thermostat. Another good place to bleed out any trapped air.

    there was no ryme or reason as to why it was so difficult. I’ve literally just put the cap on a car and watched the overflow as it heat cycles and not had problems before. I think it had to do with a bad design on an aftermarket radiator right at the cap opening on his car but I can’t prove it.

    as a reminder to anyone having temp problems:
    - Thermostat springs go into the intake
    - coolant leaks are air leaks and cause pockets
    - pressure caps go bad and need replacing, 16 psi
    - radiators get plugged up and need cleanup or recoring or replacement
    - antifreeze has to be changed every few years to keep acid levels down
    - 50/50 mix of the old green antifreeze is what a fox needs
    - fan clutches do go bad
    - fan shrouds are very much so needed

    I always have used Prestone and my motor has 1/2 million miles with the original head gaskets even though it’s been raced and sprayed and beat hard

    You aren’t going to hurt anything with too much coolant, it will puke out what it doesn’t want. Cut the top off an old milk jug to catch the overflow if you don’t want it to make a mess.

  12. #12
    FEP Senior Member Matt J's Avatar
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    Quote Originally Posted by BMW Rider View Post
    The radiator should be completely full. The expansion tank should have enough coolant to ensure the radiator stays full when cold and enough room to contain the extra coolant as it expands when at full operating temperature. Some vehicles actually had indicator marks on the expansion tank to show the correct range, but generally around half full cold is fine. If it is too full it will just end up spilling out when hot.

    On a fresh refill of the rad it is almost impossible to get it totally topped off so there will be a bit of air space in there. I usually add a bit extra to the expansion tank and after a couple of hot to cold cycles on the engine, the rad will have expelled the air and drawn back in the coolant.
    What he said...I just checked the Haynes manual to make sure I somehow hadn't missed something, and it says to fill the radiator until it's full, then fill the overflow tank to the lower mark. My 1984 had marks on the overflow tank so this isn't a post-1985 thing. When the coolant gets hot it expands and pushes out, the cap on the radiator will let this pressure out when it reaches a certain point. As it cools, the cooland shrinks and creates vacuum which will draw from the overflow tank back into the radiator. Think of it as breathing in and out. So unless the radiator is so low that it can't expand enough to create pressure, it will slowly keep pulling more fluid in until the radiator is filled anyway. You'll notice the overflow tank getting lower and you'll have to keep adding to it. Just do it up front and save yourself the time. In the "old days" before overflow tanks you constantly had to top off your radiator when it got hot and spilled out, but if you remember the radiators were HUGE, which is why you got away with/needed to not fill them to the top.

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