I've come on here this morning to have a whinge about how many views a post gets but it has no replies! Also, I have an opinion on the "expansion tank" design on our CX5s, in particular the 2,2 diesel. If anyone has some information to the contrary of what I'm about to state here, please come on and put me right.
This "level" thing, to me, just doesn't stand at all. The system has a pressure cap that in effect is a one way valve. If the pressure in the system over pressures the coolant will pass the pressure cap and end up in the "over-flow" tank. After that, the coolant that has passed to it has no way back to the system. It would just fill till it over-flows. So the level issue is that the only way is up.