Allan,
It's a mystery to me how a fluid could erode the metal impeller. I stay on
top of coolant changes so I don't think it was that. I have the distinct
impression that failure rates did drop significantly when I switched from
Italian to German made water pumps.
Ken Lewis
http://neksiwel.20m.com/

<snip> I have compared a new pump to an old
>> one. The wear on the impeller blades is very evident . So an
>> electric driven water pump might prove a healthy gain in FE (fuel
>> economy).
>
> A worn impeller is caused by corrosion and/or cavitation.  Neglecting
> to change the coolant as specified is often a contributing factor, or
> it could be poor quality materials in the manufacturing process.
>
> Allan
> --
> 1991 Vanagon GL
>
>