I thought the way go on the waterpump was only metal. However, my local parts store did not have the metal impellor when mine went bad at mile 66,666. So, I popped open the box of the one they had in stock and it was the white plastic. After looking VERY closely at what I thought was plastic, I thumped it, tapped it, scratched it with my fingernail, etc. to see what kind of material this was. It looked and acted like porcelain or something ceramic. It even rang when I thumped it. Call me crazy, but I bought it. It's been running fine ever since. I wondered about having a large metal thing spinning up at higher RPM's, too. I figured if the impellor is lighter, that will take some strain off something.
Anyway, just make sure you don't get the crap black one and you'll be fine.
