That's a good writeup on cavitation.

Having been a submarine Sonar Tech I'm very aware of how cavitation is
formed and its effects.  There don't have to be "air bubbles" in the
liquid to start with and, depending on speed of the propeller(s), a
submarine can still cavitate at great depths where there is much more
pressure than what you'll find in a Vanagon's cooling system.

Mike

Shawn Wright wrote:
> http://en.wikipedia.org/wiki/Cavitation
>
> On 19 Feb 2008 at 10:15, Kenneth Lewis <kdlewis@NORTHSTATE.NET>
> wrote:
>
>> 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
>>>
>>>
>
>
> Shawn Wright
> http://members.shaw.ca/vwdiesels
> '88 Westy 1.6TD 5 speed
> '85 Jetta Diesel 1.6NA
>