Champion's are designed to use a recovery bottle, it needs to be able to flow into the bottle when hot, and draw coolant back into the system upon cool-down. Sounds like it's just a little low on coolant, that's where I'd start anyway. Fill the bottle halfway up when it's dry and see what happens. Drive it and let it do it's thing. You may need to top it off until it finds the proper cold level; I've always added to the bottle until it stays about halfway full after sitting. Mine will fill the bottle about 3/4 of the way or so when at full operating temp and right after shutdown, then after cooling off it's half-full or maybe a little less. You just don't want it sucking the bottle dry, all that does it let it keep pulling air into the system. Now, if you absolutely can't get it to leave some in the bottle after multiple top-offs, and the radiator appears full, time to look very closely for leaks, or any signs like white residue on the pulleys, balancer, K-frame etc. Sometimes they can leak while driving, but don't leave any drips on the garage floor. Check the oil carefully as well.
Oh, and another possibility---those style bottles can sometimes be too small to control the amount of coolant that flows back and forth. That was my experience with the fancy canister style anyways..I now use a bigger plastic one for a toyota tacoma and it works great, pretty much like any newer vehicle.
