[Tom Wells]

Guys,

I think you're all correct. And further, no extra catch can is needed. As said above, if there's any water in the tank at all, that's OK.

The point of the whole system is to have NO air sucked back into the radiator or engine when the engine is cold. When it is warm, there will be water pushed into the reservoir from the radiator, then sucked back in as the engine cools.

"Working as designed."

Any extra water put into the reservoir is always going to be pushed out, so once the engine is "burped" (no more air pockets in the engine or radiator after a few heat cycles) no more water should be added.

Try hard not to overthink this...

Tom