[donandal]

I installed the radiator reservoir. I built this from .060 aluminum.
The cap is from a nissan reservoir. I copied the thread profile and
cut the threads on the lathe, then welded the neck to the top flange
before welding up the rest of the tank.

The over flow refills into the bottom of the reservoir, and any more than
that will go out the reservoir overflow at the top of the tank, then down to
the ground.