[Michael C Henry]

I have the bicycle water bottle bracket clamped to the X frame in front of the engine. The clear plastic 1 qt. bottle just slides into it with a little effort. I kinda removed the nozzle and have the hose stuffed through the cap to the bottom. I have a piece of reinforced urithane hose that I can kinda see through, running between the bottle and vent tube under the pressure cap. My radiator is a cross flow with tanks on the sides and no fill cap. Coolant goes in top left and returns from bottom right. I have a metal tube on the bottom that crosses back over to the coolant pump inlet. Radiator pressure caps originaly had one rubber seal to seal off the pressure in the system down inside the filler neck. At pressure it would vent to the tube which may or maynot be connected to a hose(usually directed to a place where coolant wouldn't cause a problem.. A small metal disk in the middle of the cap seal would open to let outside atmosphere back into the system when cooling.
Pressure caps are designated for open or closed system. The newer style being the closed system . They have the original seal and a second seal that seals against the top flange on the filler neck. The vent tube on side of the surge tanks filler neck ( or radiator filler neck ) is located between the lower system and the top flange surface. If the seal are doing there job the inside holds pressure up to the rated pressure. Excess pressure will push that seal off its seat letting presure vent into the cavity below the top seal. That is where the metal vent tube is. That hose is connected to another tank or bottle by hose. Exscess fluid is then pushed from the main cooling system into the recovery tank or bottle. When the cooling system cools and shrinks. That metal disk in the main seal opens. Rather than pull a vacume that would crush the radiator and tanks and such ,coolant is sucked back into the main system. Keeping the systen full of fluid no air that would form foam. Oh, I have metal spring inside the hoses so they won't suck flat. Also when examining a pressure cap the lower rubber seal should not be swollen out beyond the large metal reinforcement disk. Oils will do that. I installed a closed system cap similar to the one you have shown. The hose in between the vent tube and coolant recovery bottle pretty much stays full of green fliud. When system is hot fluid level in the bottle is high. When cool fliud level in the recovery bottle is lower.
Have I helped or confused you.?