How about (for a good pump) - 'One that circulates sufficient coolant for the engine under all conditions'? BTW did you find bits of the old impeller? Where did they go? When the air is cool and the thermostat fully open your water pump was able to keep up. Had the air been hotter and running the air con I guess it would boil, given time.
Good - Fast - Cheap: Pick any two.
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i
Last edited by BMWFatherFigure; 10-17-2012 at 10:28 PM.