Sorry I don't have the reference, but 3 years or so is the "recommended"
impeller replacement schedule. And that I think is based on a 100 hours or
so season. I also understand that the newer impellers are built to last
longer. My approach ... pull the outdrive every 3 seasons to lube the
u-joints etc, and while it's off replace the impeller. And then there are
people run their boats 10 years with no preventive maintenance and have no
problems :-)

"Mark" wrote in message
sgroups.com...
I have a 350 with an Alpha 1 that is overheating at low rpms. Diagnosing
the same problem last year, I had to have the water pump in the lower unit
replaced. I will troubleshoot all other possibilities this weekend
before
having to pull the boat out, but thought you folks in the news groups may
have some ideas as to what other causes it could be.

The boat is an 86 and I have owned it for about ten years for having to
replace the outdrive water pump. Any estimates as to what the life
expectancy of the water pump should be?

First I will be checking for leaks, then changing the t'stat on the engine
(as I do not recall when I last replaced it), but beyond that, Ican only
suspect either the new (last year) pump has failed prematurely, or the
mechanic I hired to do it did.

Mark (the rail & canopy hook guy)
www.ripnet.com/vtf/prod03.htm

Oops ... I read "water pump" as the engine water pump, not impeller. If it
was me, I'd pull the boat out and hook up the muffs and garden hose. Could
be someone started the engine up with no water supply ... that burns out the
impeller. Or could be the engine water pump, or risers blocked, or
thermostat, or .... could even be a faulty temperature gauge. Anyway,
running it on the garden hose should give some insight into the problem.

Agreed on the engine pump, this is the most typical cause of low RPM over
heating and OK at higher. It isn't a displacement pump like the one on the
drive, it is a centrifugal pump and as it ages, the vanes corrode off, they
simply don't sling any water at low speeds then. End result is lots of
water from driver pump, however it isn't circulated through the block, it
just get poured out the exhaust. The engine pump is responsible to move it
through the block and heads.

Common issue on cars with high mileage also, overheat at idle, OK if revved
up a bit..

Greg

"Bowgus" wrote in message
...
Oops ... I read "water pump" as the engine water pump, not impeller. If
it
was me, I'd pull the boat out and hook up the muffs and garden hose. Could
be someone started the engine up with no water supply ... that burns out
the
impeller. Or could be the engine water pump, or risers blocked, or
thermostat, or .... could even be a faulty temperature gauge. Anyway,
running it on the garden hose should give some insight into the problem.