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SUBJECT: # 27911: Replacing outboard water pump impeller
Submitted by Rob (70.18.144.40) from ALABAMA on 9/17/2008 11:23:00 PM
How often are you supposed to replace these things. I just repaced one in a 15 year old OMC motor and it looked brand new. I know for a fact that this impeller had never been replaced. I know the books says replace them every year but just wondering if this is really necessary since the pump kit is not cheap.
- 9/18/2008 11:21:00 AM
Submitted by
FreeOnBoard from TX says Depends on use
Every one of the 5 impellers I've replaced on my present V4 have "looked" good as new. Some of them were still delivering adequate cooling water, some were not. When I bought this 12 year-old boat from the original owner, I ran it enough in the local lake to convince myself that the water pump was good for another season, then headed for the coast. The overheat alarm went off on the first trip out and we limped back on the kicker. We spent most of our time at the coast fighting corroded bolts to replace the pump and concluded, as you did, that it was the original. That pump was run in very sandy water and had to be replaced again 6 months later to stop the overheat alarms. The next replacement was convenient because I had the motor torn down for a powerhead replacement. That pump lasted 4 years, about 250 hours of running time, without incident. Its replacement lasted about 150 hours of running time, when overheat alarms and a noticeable decrease in the indicator stream happened at the same inconvenient time. Early on, I installed head temperature gauges, thinking that as the pump became gradually less efficient, I would see a gradual increase in operating temperatures. I've since concluded that the pump has so much excess capacity that it will provide adequate cooling right up to the point where it's ready to completely crap out, at least in my V4; might be different in a V6 or a V8. Several folks on this board have recommended a water pressure gauge as a way to keep track of the water pump condition, and that will probably be my next project. Since this motor accumulates only 50-60 hours a year, replacement every year does seem excessive. If I lived near the coast and had the time to rack up 150-200 hours each season, my attitude might be different.
