Water definitely erodes piping systems and other parts it moves through.
Water jets can be used to cut steel and concrete. Cooling system erosion
is a common source of failures. What do you think really happens to heater
cores and often radiators? The erosion wears the tubes making them thin
enough to leak. Automotive coolants can make things worse as part of the
corrosion control package is abrasives. These abrasives are also what
wears out the seal set. On the Vanagon, things are made worse as the
engine is often working at some 4,000 rpm. The water pump is spinning
almost twice as fast. No wonder those bearings often say no more. Using
high mineral tap water also adds to the water wear problem.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Kenneth Lewis
Sent: Tuesday, February 19, 2008 10:15 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Electric Water Pump

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
>
>