I understand that, but with the neck & cap at a 45* everything above the bottom edge pours back out when you remove the adapter.
I forgot I did a poor mans version of the filler and it's what lead me to understand the problem. It's been a few years. Afterwards I had to tilt the car to get enough air out and coolant in. You can see how low the filler is on this dumb radiator.
Later
When was the last time you *really* did something with your Z to call yourself a Z enthusiast?