Your correct in that they will last a long time. I have gone for long times
as well. It is more of a matter of knowing for sure that your not going to
have a problem.
Rarely do they actually go completely out.
They will over time tend to not produce as much pressure as they should.

Kind of like changing your oil. Some do it 3000 miles, some 5000 miles,
some 7500 miles, some 10000, some 15000, some never. Yet the car still
runs.

Or like timing belts on cars. 90000, 100000, never...

Most change them every 2 to 3 years just as a precaution.


--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"trainfan1" wrote in message
...
Jeff Rigby wrote:

-VI


Three reasons to replace the impeller with normal use. 1) Dirty water or
idling in shallow water can cause the impeller to wear out prematurely
(sand). 2) The impeller becomes less flexible and can loose it's shape
causing less water flow and poor priming (apx two-three years) . 3)
catastrophic failure because the rubber rotted (Aprox 5+years).

Another good reason to do it often is that the bolts will be easier to
remove.

Outdrives are easier to pop off and replace the impeller (45 min for me).

The impeller materials must not be very good anymore...!

My outboards:

-1972 Johnson 6 hp - original impeller - never a problem.
-1973 Evinrude 115 hp - changed once ~1991 while apart for straightening
the prop shaft.
-1975 50 hp looper - retired in 1986(still have it, though) with original
impeller
-1981 Evinrude 115 hp - not changed since I bought it in 1997.

When I was the tech for a 50-60 boat rental fleet, about 1982 - 1987, we
had all Johnson & Evinrude - lots of 5.6 & 6 hp, 9.5 & 10 hp, 18/20 hp,
many 28-33-35-40 hp, some '76-up 35's, 55-60-65-70 hp loopers, even some
old "pumpkin" V-4's, I cannot recall changing a single impeller.

For two months a year, they never sat still for very long, though.


Rob