well i figured out why my koyo radiator came with a plastic "bleed plug" to purge air instead of an aluminum plug. 2 weekends ago my upper heater hose failed at a track event but no apparent permanent damage to the engine. replaced hoses tonight, refilled radiator, but i cannot unscrew my aluminum purge plug from my radiator more that 1/2 turn. guess i should have coated it with anti-seize compound...lesson learned. something for others to consider...