Coolant Expansion Tank...

Discussion in 'Fox 5.0 Mustang Tech' started by TrophyHead, May 10, 2014.

  1. Should these tanks be completely sealed or opened to atmosphere? If sealed how does the escaped pressure return when the radiator cap re-seats?

    I'm not thinking clearly and need this answered.
  2. Factory setup is open. Needs to vent excess pressure. Radiator cap should hold about 16psi
  3. Thanks Madspeed. I'm going to vent this tank to atmosphere.
  4. On Fox body Mustangs, the system is pressurized on the radiator side of the cap and has only atmospheric pressure on the overflow tank side of the cap. The recovery/overflow/puke tank vents air to make room for the expanded coolant when the coolant pressure exceeds the pressure rating of the cap. (It used to be cars just spit up coolant onto the pavement without any recovery and just sucked air back in.)

    As the cooled coolant creates a vacuum in the radiator side of the system, a little spring in the radiator cap allows fluid from the tank to be sucked back in to the pressurized part of the system. Air from the atmosphere replaces the recovered coolant in the overflow tank. If the car really overheats, has the tank overfilled, or has a head gasket problem, it can overflow the overflow tank and still spit up on the pavement and your battery area.