I disagree with SVTDriver.
Here's the scoop:
Black plastic is likely to fail in another 60,xxx miles. Be ready to change it before this. It WILL work, but not reliably after those miles (don't use it longer than that)
White plastic.. will work much much longer.. there HAVE been a few white plastic failures, but I can count them on one hand at 100,xxx + + + + miles vs the 363,536,738,267.8 failures of blacks.
Metal impellar ones can't shatter, but they CAN leak around the shaft, etc. Some have experienced this problem, most have not.
Your call but I recommend the white plastic, personally.
As long as you collected all of the pieces of the impellar from the broken one (try to piece it together like a puzzle) you are fine.
The impellar half is all you need. If you can't find all the pieces, or are unsure at all, flush the system as documented fairly well in the maintenance how-to FAQ to ensure no pieces become lodged (preventing flow anyway)
Ray
