I put a mark on my rec tank that is very easy to see..

Winter it is a hair under the mark, but on warmer days it right on my mark..

It's a bit higher than stock fill. But not so much that it would ever overflow in summer etc..

update i found the source were it was leaking after i filled the bottle up it was leaking were you fill the radiator tee part were the cap goes on under were the seam meets you can feel it bowed like were the seam meets..I mean the whole tee is plastic like you would buy from prestone to do a flush ,you chevy should at lease made that part out of aluminum,well is this a dealer part to order or can i find it somewhere else ?

Mine had the radiator hose rub through and leaking where it touched the manifold to brake booster vacuum hose. They replaced the radiator hose, and covered it with a corrugated plastic cover.

Mine is still fine this way.