Dennis, actually some of the newer VW engines have water pumps with plastic impellers stock from the factory.  And these wps are usually the ones that are run off of the timing belt.  The ironic part is the all of the aftermarket pumps have metal impellers.  So I would say if you are have a newer VW car (say after 2000) it would be a good idea to replace the water pump when you do the timing belt just to be safe.  The wps with the plastic impellers are very prone to self destruct (that is what I have heard too).

Ken Wilford
John 3:16
www.vanagain.com

-------------- Original message --------------
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>

> Who gets rebuilt water pumps for Vanagons or Jettas? Thoe worst I have
> seen is the GMP brand. Stamped metal impeller that just does not move
> enough water at idle. I have never seen a plastic or composit impellar for
> a VW application.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Allan Streib
> Sent: Tuesday, February 19, 2008 10:50 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Water Pump Impeller Damage
>
> neil N writes:
>
> > Got some advice on brand names for replacement and was advised to
> > get one with a metal impeller as the stock plastic one self
> > destructs. I pulled it and sure enough, the plastic was
> > deteriorating! Not sure why, but maybe something to do with a
> > chemical reaction?
>
> By the way, if you get a "rebuilt" water pump then be sure to check
> the impeller before you install it. I bought one for a Jetta years
> back and the impeller had visible, fairly significant cavitation
> pitting right out of the box.
>
> Allan
> --
> 1991 Vanagon GL