what Vern says - note that you're usually adding water when it's cold, as temperature goes up, water expands
if you check the level when it's up to normal temp, it should still be at least an inch or 2 down from the fill neck

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot