expansion tank
to be a "recovery" tank does it have to be sealed accept for the hose running into it in order for it to create the suction to pull it back into the radiator? or does it remain vented?
The hose from the radiator needs to be under the coolant level in the tank and the tank itself needs to be vented to allow the coolant to replace the air in the tank and pull it back without restriction.
That tank I made was actually a thermos and the hose from the radiator goes into the bottom of the inner liner with fittings and rubber washers for sealing to the tank. (it sticks up a half inch inside so it doesn't recover bottom gunk)
The vent is on the inside of the tank at the top and it vents between the layers and out the bottom of the outer tank shell when it needs to vent or actually overflow the tank itself. (It never has, but it could if needed)
With a recovery type cap you could literally have a hose running into a mason jar with no lid on it, and it would still work like it is supposed to.
The recovery type cap allows coolant out to the recovery tank only when the pressure in the cooling system gets higher than the cap can hold back (12-17lbs or so) like expanding fluid with no air gap needs.
Then when the system cools down and the coolant contracts again leaving room for it in the radiator, the contracting causes a vacuum and that little valve on the cap picture I posted has a very light spring holding it closed, so the vacuum can pull the coolant back into the radiator.
The three critical points are that the recovery hose needs to be submerged in the coolant to recover it, and that the recovery hose from the radiator to the recovery tank HAS to be air tight.
AND the tank needs to be vented somewhere towards the top to atmosphere to allow the fluid to move in and out of it without causing a pressure or vacuum in the tank.
