I just changed the water pump in my 25 HP Johnson, and not a moment too soon. Thought I should post a reminder outboard motor owners out there, probably the most critical part of your outboard is the water pump. If the pump goes out and you don't notice in time, it's fried outboard for dinner. Not good.

Essentially, the water pump is a wear part like tyres on a car. Eventually, it has to be replaced because the rubber impeller will wear away. I've long been told that the water pump should be changed every 10 years at the absolute longest and every 7 years if running in river water or salt water where silt and corrosion wear.

I've had my 25 HP motor for 7 years so I figured it was time. I assumed the previous owner changed the pump at some point because the motor is a 1985 model. Bad assumption! I really dodged a bullet as the pics will show.

Here's a pic of the water pump with the impeller exposed. Notice how thin the tips of the impeller splines are worn.



I found severe cracking in each impeller blade, here's the worst, this blade was about to tear free, but all the blades were cracked to some degree.





Notice how thin the tips of each impeller blade are. Look at the one my index finger is on. They should be about the same thickness at the tip as at the base next to the hub. That's what running in river does to your engine.



I've seen worse, but this one was pretty bad.

So if your outboard is 7-10 years old or more and you don't know if or when your water pump was last changed, I'd strongly suggest either doing it or having it done. It takes about an hour for me to do one, obviously an outboard mechanic should be able to do that in half that time. It's not terribly difficult, but I'd say you'd best be a competent intermediate mechanic an have good instructions if you haven't seen one done before.

I replaced the whole pump, but you can replace just the impeller providing the pump chamber case isn't worn badly, which mine was.

Keep it running cool.

Grouse

Now you see as a salty sea dog, and having owned outbnboards for 25 years, I'd change the impellor on every second yearly service - but check it each year.

7 years? Where did you get that figure from?

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Agree check impellor for wear every year, replace ragardless every second year.

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What I'd heard is to change out the entire pump every 7 years if running in anything but clear water. I looked at the manual and back in 1985 they gave no specific directions for maintenance duration for the pump or impeller, but as always follow you own manufacturers instructions and/or experience.

With the number of guys inquiring on here about used outboards, I just wanted to show what can happen if you assume a previous oner kept up on the maintenance. I'm not sure if this pump itself had EVER been changed. The impeller was probably changed at some point in the distant past, but as you can see I should have changed it years ago myself.

Grouse

I destroyed my impeller driving through silty/sandy water so it can easily happen. Shop around online for impeller replacements as i was able to get 2 online for the price of one in a local yamaha dealer

Good advice about the Impeller. Got my Yamaha serviced by a guy who works at engines!!! Was told the pump had broken and that the engine was wrecked. I was not a happy bunny because I am particular about the engine. BROUGHT THE ENGINE TO yAMAHA DEALER Floods in Omagh It was the impeller that was at fault. Never again will I bring the engine to "somebody who works at engines. The impeller is changed every 2 years now and inspected yearly.
It's a 2 stroke 8hp Yamaha and is 26 years old. Goes like a dream.
The other thing to mind are the rubber blocks on either side of the main shaft. THEY WEAR AND CAN ALLOW SOME VIBRATION ALONG THE SHAFT TO THE PROPELLER. WELL WORTH CHANGING THEM
I changed the propeller last year--a few bends in it! New propeller makes a huge difference to the smoothness of the engine. 2 strokes are great engines and 8 hp is enough for me.
I fish on Melvin

Interesting comments on Yamaha and they both support what I was told by a Yamaha dealer in Canada two years ago. I'd asked about a used Yamaha he had for sale and was generally chatting about Yamaha outboards compared to Mercury and Evinrude/Johnson.

He went on to tell me that Yamaha 4 strokes in particular seem to have a water pump that is very sensitive and the impellers wear very quickly compared to other models. He had been warning his customers to replace impellers and pumps frequently. He didn't say how frequently, but he did make a point of saying they wear out much faster than other brands and he deals Mercury and Yamaha with mechanics working on all other brands.

Anyway, my point was that if you haven't personally had your pump or impeller changed within the manufacturers recomendations or if you're buying a used outboard where you don't know the maintainance history, you should certainly have either the impeller or the whole pump changed.


Grouse