[Joyridin]

Where do you have the steam ports on the heads run to? The radiator? Is the outlet above where the steam ports are located?

I have drained/filled my LS3 about 10 times and never had an issue. I fill the radiator, then fill the overflow about 1/2 way. Run it until the thermostat opens, then shut it off and let it cool. Check levels and add to both if needed. Do the same thing again. You might have to add to the overflow, but usually not the radiator.

I had one of those SS overflow tubes like you. When it got hot, it would overflow slightly. When cold, it was empty. Maybe yours is bigger than mine was, but it didn't work really well.