I posed this in another thread but I don't think it gets much traffic so I'll try it here. I've heard a couple of times that the degas bottle is a flow-through device. Looking at it, logic defies that theory and I'm hoping for some learning up on how it occurs. I just gots to know. There are two openings in the bottle, one at the bottom and one at the top (I figured that out all by myself). As the radiator fills, so does the degas bottle from the bottom after the level of coolant in the radiator reaches the height of the degas bottle and the level in the degas bottle would then reflect the coolant level in the radiator like a sight glass. As the radiator fills, the air being displaced should escape to the degas bottle through the top hose though it does burp up through the bottom of the degas bottle somehow if you fill the degas bottle quickly. I filled mine slowly with a siphon out of a 5 gallon bucket with the coolant mix in it and there was no burping done. Now...when filled to capacity, the top hose that runs from the degas bottle to the radiator sits above the coolant level and I'm thinking that it should just let air flow back and forth between the bottle and the radiator and that as the coolant expands with heat, the degas bottle will fill from below like a sight glass in a furnace or any other system with a sight glass fill monitor. Am I right or am I wrong?

 

It is an expansion tank, not really a flow through, when hot, coolant and vapor nead a place to expand into and release the pressure it does this by expanding into the reservoir and venting out the cap.
I would imagine that the coolant flows up from bottom as it expands, as well as maybe from the top if super hot.
Sounds like you have the correct way of seeing it