Water Pump Impellers Service Life

[Rick W]

I have a question regarding the water pump impeller. The outboard I am thinking of buying has an recommended interval of 300 hours between impeller replacement cycles.

Q1: If the boat has only run in fresh water why would one need to change the impeller at 300-hours--or for that matter at all?

[To jimh specifically in a prior thread about E-TEC engines:]
Q2: Did you notice any wear (erosion or corrosion) on the impellers that were removed from you're E-TEC?

I am assuming the maintenance recommendation is based on erosion and corrosion concerns and the maintenance interval is based on most adverse operating conditions , which would be saltwater v. fresh water.

[Jefecinco]

Pump impellers with 300 hours of use should be replaced regardless of the water in which it has been used. All water has mineral content and getting some muddy or sandy water into a boat engine is almost unavoidable. Generally the water around a launch ramp is shallow and that makes getting some unwanted material in the engine very easy.

Impellers may also take a "set" as the blades are squeezed by the pump body at all times. That can cause cracking where the blades bend. When an impeller is replaced the wear plate should also be replaced because as it wears it reduces the pump efficiency. As the pump is apart it adds seconds to replace the wear plate.

Replacing the impeller is a smart preventive maintenance measure. If the impeller begins to come apart while the engine is operating the pieces can be spread throughout the engine cooling water jacket and plug passageways. Engine damage can result due to over heating. Water pump rebuild kits are available that include the needed gaskets and wear plate.

[Rick W]

Great points on launch site grit, turbid waters from run off, low water level use, salt deposits from salt water use--all introduce risk to the cooling system function.

They are all good reasons for the preventive maintenance task of inspection and replacement.

Any preventative maintenance task introduces a small probability of risk.

Q3: What if the technician repeatedly replaces the impeller but neglects to change the wear plate or he puts in the wrong impeller with slightly different dimensions?

If the outboard has a temperature gauge, the normal running temperature should be noted before and after water pump maintenance. If a warning light is all there is it might be a good idea to use one of those heat measuring guns to periodically check the engine and the thermostat function. They are now inexpensive tools.

If you suck up a bunch of sand, a single event could cause more wear than 300 hours of typical use.

[biggiefl]

Don't think too much about it. An impeller kit is cheap as are thermos. I rarely change thermos unless they start acting up. Water pump I do usually every 3rd season.

[L78steve]

I've been told by commercial flats fisherman that they wear out their outboards before they change pump impellers.

Impellers may take a set when unused for a spell but quickly rebound with use.

I personally got 15 years out of an impeller before it failed.

Now if you are crossing the Okeechobee waterway expect some accelerated wear and tear.

I've found that the stainless sleeve cam wears faster than the rubber in abrasive waters.

[jimh]

[To jimh specifically in a prior thread about E-TEC engines:]
Q2: Did you notice any wear (erosion or corrosion) on the impellers that were removed from you're E-TEC?

No. The impellers looked fine, and I keep them in the boat toolbox for emergency spares.

[jimh]

Q1: If the boat has only run in fresh water why would one need to change the impeller at 300-hours--or for that matter at all?

I recall a Michigan Boston Whaler owner who had a c.1992 Yamaha outboard (a two-stroke-power-cycle engine). He went ten years without changing the water pump impeller. A very experienced outboard engine dealer told me that when Yamaha was making inroads in the USA with their outboard engines—as was occurring in the 1990's—Yamaha used very high quality wear parts—parts like propeller shaft seals and water pump impellers—which gave their engines very high reliability and freedom from chronic repairs. This helped Yamaha build a reputation for longevity are reliability.

In comparison, some domestic manufacturers—Mercury as I recall—in that same era specified that their water pump impeller should be changed every year, and that was probably a good idea, as they used impellers that really needed to be changed once a year.

Of course, the cost of a Yamaha water pump impeller as a replacement part was probably five times the cost of a Mercury impeller.

ASIDE: back to the Michigan Boston Whaler owner, after about ten years of completely trouble-free operation of his Yamaha, in c.2002 he finally decided to have the engine serviced. The shop performing the service goofed up something in the electrical wiring, which resulted in a current path from the battery positive to the engine chassis, although a very low current path. The effect of this was that when the boat was back in the water, a white deposit immediately began to appear on the stainless steel propeller. That was the zinc of the sacrificial anodes being eroded at an alarming rate due to the stray current. This was a good example of sometimes it is better to leave well enough alone. The service shop did find their error and fix the problem before any real damage occurred.

[jimh]

When Evinrude introduced the E-TEC they emphasized that the service interval—including the water pump impeller—was three-years or 300-hours. As I recall this announcement was met with skepticism, calls of heresy, and dismissed as nothing more than a misleading marketing ploy.

With the introduction of the latest Evinrude E-TEC engines under the G2 family, the E-TEC G2 owner's guide now indicates the water pump should be replaced at an interval of five years or 500-hours. We've gone from annual replacement of the water pump to five-year or 500-hour intervals.

Cf.: page 42 at G2 Owner's Guide