Depends on the cap. I was talking to Grant. If you don't have the correct cap it won't suck water back into the radiator. That is why a lot of overflows drain to the ground. He said fill the Radiator, run it. What ever water drains out that is the normal level for the system when hot.
Why would you treat the system any different than a car?
I have no clue. that is what I was told by Grant. I think that once the proper level is reach hot it doesnt matter
Add a 1/8" NPT or -3 (or whatever size it is) bung to the radiator near the inlet or on the inlet tube itself (near the radiator).
I'm in the middle of swapping my LS over to another frame. When I pulled my radiator, I was shocked to find some rust in my Dex-Cool out of the radiator. Plenty burnt looking coolant but when I flipped my reservoir upside down to drain, brand new dex cool came out! As if it never went anywhere. I blew the lines with my mouth and there was plenty of air flow. Didn't like that one bit. My rad cap is the old style Stant red flipper flapper thingy which I thought would be perfect. Now I'm not sure.
It probably burped out the first time you swapped the coolant, then chilled there until now.
Unless it was hooked to the wrong tube & it was trying to suck off of the head space instead of the tube that actually goes down into the fluid. yea......... Ive NEVER done that. LOL.
