Coolant tank

Ideally it’d be somewhere in the middle

 

What he said

 

I feel mine up to the maximum level when cold. And no need to top as of yet.

 

The thing about resivors is they are the visual of what is happening with the inside of the engine , along with the oil. In the case of the res, it provides additional water when needed , and storage for when it isn't .( when it 115 degrees out and your engine is getting a little hot , it uses a little bit more , and reverse in fall -winter . ) the space from the bottom of the cap to the full line is a safety measure so that the fluids have a place to go instead of a bypass / overfill tube .

 

Minimum cold. Maximum hot. If there’s a few inches or? between max mark and top of tank, You can get away with adding little extra, Maybe half of the difference. Don’t want to overfill it and have the hot expanded coolant crack the plastic tank.