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Radiator Cap?

Discussion in 'The Garage' started by Dallin, Mar 3, 2006.

  1. Dallin

    Dallin 1/2 ton status

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    Can someone explain how the radiator cap and over flow system are supposed to work? I just got a new radiator. With the radiator sitting on the garage floor I installed the cap. I thought if I blow into the overflow tube it should be blocked. So, I tried it, but the tube is open to the radiator and I can blow straight through. Does this mean I have the wrong cap? I noticed the radiator cap has 2 different sealing surfaces. One is above the overflow hole and the other is below it. When do the seals open to vent pressure or fluid?
     
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    The cap has a spring loaded sealing washer that is forced up and open when the pressure is higher than it's pre-set spring-loading. This opens the rad to the overflow tank and allows excess coolant to escape. When the motor cools the suction/vaccuum from the cooling system sucks the coolant back into the rad.
    If you have an outlet below the sealing washer this will be for another application like carb warming or some part of the system that is in constant use on the pressure side. It's not for the overflow tank.
     
  3. Dallin

    Dallin 1/2 ton status

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    That's how I thought it should work, but how would the fluid ever get sucked back in? The vaccuum would just pull the seal down tighter. I have no outlets below the lower sealing surface. Just the standard overflow outlet between the sealing surface.

    While I lay awake last night thinking about it I came up with this. Maybe the spring is like a thermostat spring that opens when the vehicle is cold allowing fluid to be pulled in. Then when the radiator warms up the springs pushes down and closes the system. If the pressure inside got over the cap rating it would burp some fluid out into the overflow tank like southerspeed described. Can anyone confirm this?
     
  4. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    If u look inside your cap you'll see a smaller valve and sealing washer that seals when it has pressure against it from the rad but allows coolant to be sucked back in when there is vaccum in the rad.
     
  5. Dallin

    Dallin 1/2 ton status

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    I'm not following you. When you say look inside the cap do you mean look in the hole on the radiator? The cap has a top and bottom but not an inside. Maybe I'll take a picture later today. I really think the spring on the cap extends like a thermostat spring when it's hot. I might dunk it in boiling water as a test.
     
  6. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    OK, turn the cap upside down and look at the spring loaded sealing 'disc'. In the middle of that is another valve that allows the return of coolant to the rad.
     
  7. Dallin

    Dallin 1/2 ton status

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    I found the valve your talking about. It all makes sense now. Sometimes I'm a little slow. Thanks for your help.
     
  8. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    lol. you're welcome. I should've taken a pic. It would have been much easier to explain!:D
     

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