i have 30 plus free just cover the shipping lmk dave

My personal experience is that over filling impedes the overflow. The column in the tank is too heavy for the coolant to push up. YMMV.

My personal experience of over 10 years doing this, is that it has no effect on the overflow.. Just saying..

YMMV means "YourMileageMayVary"

When I was having troubles I found that a near full tank did not get any fuller after warm up. But lowering the level it did. Maybe I had something else going on, don't know.

But why would you have a near full tank on cold engine ? I don't get that. I would have vacuumed most of that out. & the YMMV, I was wondering about .. LOL

Strange, my tank will rise 3 inches or so after good running. Then overnight it goes back down to my mark.

The reason I never liked that factory level was it was at kinda almost empty point, & if it ever did go lower, it might suck in a bunch of air..

If it is near the bottom when cold, that means the radiator has already sucked everything it needs, leaving plenty of room for overflow when the engine warms up. Depends a lot on your definition or "near full", and as I tried to indicate there was experimenting going on.

Cool, hope your experiment was successful..