That seems pretty cool, mine runs around the halfway point all the time after it warms up, and water never spews. :blink:
That radiator sounds funny to me, I don't have plastic ends, though my bro's T/A does, and he had to replace it because when it did blow it was nasty. Also, try putting the old mechanical fan on it, and replace the fan clutch, it sounds like it was going out since it slowed down when it got hot.
Fluidyne radiator with fans:
http://www.suprastore.com/copa.html