Coolant questions (one is probably dumb, the others maybe)

[re_buchanan]

never mind: I think I found a hint in a previous post "mix flaps in the heater box"

here's my guess: the heater core can either have hot coolant coming directly from engine or cool coolant from the radiator - the mix flaps control the ratio of hot-to-cool coolant - so if I don't turn on the heat, I can have an air bubble "behind" the/a flap

[FjordMoCo]

Sorry I wasn't more clear. In a heater system like ours, the heater core has a permanent flow of hot coolant. Cabin heat temperature is controlled by flaps inside the HVAC box which allow greater or smaller amounts of outside air, air-conditioned (chilled) air, and heated air to mix.

An older system that uses a valve in the heater core coolant hose controls cabin heat by restricting coolant flow to the core, thereby lowering its temperature.

My initial uncertainty was because I have much less experience disassembling these new-fangled cars.

[re_buchanan]

Sorry I wasn't more clear...

Actually, this is how I initially read your post.

Apparently, I over-thought it trying to understand where the "trapped air" that JDS60R mentioned would be and how running the heater would clear it or could otherwise affect the flow of coolant through the heater core.

Thanks