440 6bbl Radiator is clean, thermostat is good and less than a year old, nothing leaking, water pump checks out. Running 50/50 with a bottle of red line water wetter. The car does not overheat even in the really hot weather we've had. Temp gauge works and stays steady once warmed up. I had it out Sunday in 95 degrees for a 50 mile run with no issues. Most of it was interstate but some stop and go. Here's the problem: For the last several times I've run it, when I shut it down, the radiator will puke maybe between a pint and a quart out the overflow. The first couple times I thought maybe I just had it overfilled but it didn't look like it when I took the cap off. After the run and puke Sunday, I checked it out and the coolant level is just over the core but a couple inches below the top of the radiator so I don't think it should have done that. Any ideas?