How does antifreeze move between sections of the Degas bottle? I notice during operation the small section connected to the upper hose of the Degas bottle rises in its fluid level. It sits at a higher level than the main section of the Degas bottle. I notice if the pressure cap is removed and the "screw" is removed from the small section the two sections equalize and fluid moves back into main section. Is it normal that these sections don't seem to equalize on there own?
I'd also like an explanation of what's going on with that antifreeze reservoir. I also need the procedure to DIY an engine coolant change
As far as I know, there's just a partial-height baffle in there so you can more easily visually confirm that coolant is flowing, as the level will be higher on the upstream side. I don't think it contributes any magic to how the degassing works. It's pretty simple. The older, overflow-bottle systems had coolant in a bottle connected by a single hose to the radiator filler neck, outside the inner element of the pressure cap. That bottle was kind of a stagnant backwater, except (a) when the engine heated up, and some coolant would press out past the pressure cap, into the bottle, and (b) when the engine cooled, and some would be sucked back in. When it worked right, there was never supposed to be any air-filled headspace in the radiator, which needed to be filled to the top. In the degas-bottle system, the bottle totally participates in the coolant circulation. There's a hose out and a hose coming back (likely from some strategically-chosen high spots in the system). Any air bubbles getting pumped through the system ultimately wind up there, and the bottle is made with enough headspace over the F line for the air to just stay there. The benefit for you is the coolant change should be a lot easier than in the older systems. In gen 3, you just refill until the degas bottle is at B (a line somewhere above F), cap it, and run the engine up to temperature and several minutes longer, then shut down and let it cool. After cooling, you should find the level pretty much at F, just like the engineers knew how much air would be in there to circulate out. In your gen 4 bottle, I'm not sure I can make out a B line, and also you mention a "screw", which my gen 3 doesn't have, so it's possible they tweaked something for gen 4, and the procedure in that repair manual (which I don't have at hand) would be the straight scoop. Still, I suspect it will be about as simple as gen 3's is.
