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Changing oil, spark plugs and filters all fall into the preventative maintenance category, things which we do to both keep our engines running properly and prevent significant problems from occurring. Changing the water pump’s impeller is often included among these tasks and for those with inboard diesel engines, or those with outboards on boats which are used seasonally or are kept on trailers, it’s probably easy enough to do. Unfortunately, in order to access the impeller on our Yamahas, the engines must be pulled out of the well and the lower units must be removed, tasks which are difficult enough to make this something that does not get done as frequently as it should. At least by us that is.

Note: Our friend Drew wrote on his blog how he pulled the lower unit while in the water! Crazy? I think so!

For those who are not up on the role of the impeller, and I would certainly have included myself in that group not all that long ago, the impeller is part of the raw water pump which draws water into the engine to cool it. Without it functioning properly, the engine will overheat, something that ours was definitely doing. On a properly running outboard you can typically see a “pee stream” of water exiting the engine when it is operating. This tell tale does not guarantee that the water pump is all OK nor does a lack of it mean that the water pump is not functioning. It is a good indicator though and we try to always ensure that we see this stream when the engines are first started.

Although we did observe the stream prior to our experiencing our engine issues, no water was flowing when we began troubleshooting it. Additionally, the engine was running very hot, another symptom of a cooling problem. Always checking the easy things first, we got in the water to remove the water intake plate to see if it was clogged. It was there that we saw little bits of black rubber, a sure bet that the impeller was toast. Given that I had never changed it, that was not all that surprising for me.

Like all maintenance jobs that we do for the first time, we entered into it with a tiny bit of apprehension. We had read about the difficulties of separating the lower unit from the main part of the engine and were not eager to have that kind of fight. Fortunately for us, pulling the engine, a job which we had done before, and removing the lower unit actually went quite well. In truth, we were feeling quite good about ourselves when we removed the water pump housing and saw that our assumption was correct, the impeller had indeed been trashed. As luck would have it, our repairs went downhill after that though.

All ready to raise the engine. We re-tasked the block and tackle from our dinghy davits for this job.

Our outboard engine “work bench.”

The lower unit removed. Things went downhill after this.

Do you think the impeller needs to replaced?!?!

All documents that I have read state that if you’re going to go to this much trouble, you might as well replace all of the serviceable parts in the water pump instead of just the impeller. No problem for us, we have a water pump service kit for just that purpose. The stumbling block to completing this though was removing a pesky little piece of metal called a woodruff key. This half-moon shaped disk fits into a slot in the shaft and when mated to a groove on the impeller, forces it to turn with the drive shaft. Unfortunately, it needed to be removed to access the other parts of the water pump. Do you think it would come out? Not even maybe. We tried pulling on it with various types of pliers, dousing it with penetrating lubricants, tapping it every which way and even heating it for a bit with a lighter. None of those solutions worked. In cases like this, we always consult the Oracle to see if we’re missing something but without decent internet on the boat, we couldn’t even do that.

Problem two reared its ugly head when we turned the water pump’s plastic housing over to inspect it. It was then that we saw how the remnants from the impeller had all melted inside of it. I believe the housing itself was actually melted too but even if it wasn’t completely trashed at that point, it is now. I messed it up trying to remove the metal insert. πŸ™

Have you had enough bad news? Well, here’s the good news. Following a trip to shore to get internet, Rebecca found a source of water pump repair tips that included a method for removing the woodruff key using a chisel. Did it work? I am happy to report, yes. The second bit of good news is that the water pump housing that we destroyed is not a super-expensive part. They sell for only $30.00 on and I have since ordered two, along with another water pump service kit for the other engine. These parts are being shipped to our daughter’s and we’ll pick them up when we’re in California in 2 weeks. Remembering what I wrote yesterday about St. Martin being a great place for repairs, there is still a chance that I might find the part I need to purchase here and assuming that I can, and it’s not stupid expensive, we’ll pick one up. Until such time that we do obtain that piece, our starboard engine is going to be living on our cockpit floor. We’d much prefer to get it back in the water though.

The pesky woodruff key!

The water pump housing. Yeah, this doesn’t look good.

We definitely deserved a drink after all that. Frozen Mojito at Barnacles… MMMM!


  1. I am constantly amazed at your ability to troubleshoot and repair things yourself. I am not mechanical in the least and I recall back in high school, a new option was offered where, instead of the usual split of girls in home-ec and sewing classes and guys in the woodworking and mechanic ones; they offered a class where everyone spent 6 weeks in each option (and it also included drafting class and maybe one other). I signed up thinking it would be really fun. When it came to the mechanic class, we had to disassemble and reassemble a lawnmower engine. When all was done, mine was the only one that wouldn’t run. πŸ™

    So I am always in awe of you being able to repair so much on your boat!

    • I wish that I had taken those classes in school too!!! All I took was electricity classes.

      To be honest, we amaze ourselves sometimes too. Today was NOT one of those days though. πŸ™

  2. I love it! Housing is kaput, so let’s go get a Mojito! πŸ˜‰ Any luck finding parts there?

  3. You sure did cook it! Don’t you just love going where you’ve never gone before, learning and not have it cost a fortune?

    I didn’t follow the link but I’d think if you had a calm shoreline to bring the boat to, you could just drop that lower unit into your hands.

  4. Hey guys… good on ya for your attitude and tenacious spirit regarding self-repair. Although we are not cruising/sailing yet (difficult in Central Alberta!), that is how we intend to spend retirement. I grew up on the west coast, so I know sailing pretty good… it was repairs that freaked me out!
    Fortunately, I work in the oil patch, with a well-serving company and drive large tractor-trailers on roads that weren’t even built for quads! But those years have taught we an immense amount of mechanical know-how that will serve me for a life time, or life on the water! The crews I work with are also AMAZING when it comes to temporary life or death repairs on the spot…

    Btw, I LOVE reading your blogs! Keep ’em coming, and keep the wind at your backs!

    PS – I recently purchased a TRX… I spend two weeks at a time in various hotels… I believe this could be a winner as far as maintaining an exercise discipline while on the road…!

  5. I find it awesomely amazing what you have to do to out there Mike. You and Rebecca stay safe.

  6. @Sandra, I also took a mechanics class in high school and my lawnmower wouldn’t run after reassembly either. The instructor couldn’t even figure out why it wouldn’t run. So he and I tore that lawnmower motor down again. And Mike, you know what it was? …. It was that stupid woodruff key on the flywheel. The old key had sheared just enough that the engine would not fire. So always replace those keys to keep everything lined up perfectly.

  7. I would always just replace the impeller and put it back together. I think most owners of old outboards ( an IO’s ) learn this. What is most important, and most fragile, is just the rubber impeller blades, and the best thing is to change them pre preemptively. This isn’t a big deal at all though. The real danger would be if you didn’t do it and cooked the motor.

  8. No, I am not crazy! The day I replaced the water pump while swimming it was about 100 F and I had done several before. It was actually rather laid back and nothing went wrong, just not what I wanted to be doing after a day of sailing.

    Usually before they fail completely you will clog the pee hole with a few impeller bits. Not always.

    It is a good to do this when you haul the boat for bottom paint. The geometry, with the boat on blocks, is actually pretty good. No advantage to pulling the engine then. The boat gives nice shade.

    Wow. Really melted. A tap with a chisel is the standard way to pop that out, and come to think of it, I’ve done that a few times. Since you have the motor on your cool work stand, I would certainly pull a few hoses and a few plates to see if there are too many impeller bits floating around, clogging things up. Most of the time they blow through, but not always. Certainly pull the thermostat; it’s on top and could probably use a cleaning anyway. Gently. They get pretty corroded.


    A dumb thing I did… twice… was raise the engine while it was still idling and forgot about it for an hour of so. We needed to save gas and were running on the other engine, and so I didn’t hear it. I guess I idled one down to see how our speed would hold, and then lifted it without thinking. Surprisingly, the engine didn’t get that hot and didn’t ruin the impeller. I guess idle is so slow and there is so little heat in the engine, air cooling did enough. But dumb. Perhaps it contributed to later problems.


    Been there, done that, bad memory. The most likely collateral damage from over heating, for you other readers, is damaged oil seals. Very bad.

  9. the metal insert in the water pump housing come out.

  10. I missed telling y0ou guys Merry Christmas, so I hope you had a good one. And a Happy New Year to you, as well. May the new year bring you fair winds, following seas, and only those problems which you already know how to fix!

  11. Ouch. I don’t think I’ve seen a housing that bad before… they’re usually steel or aluminum and a few minutes with a scraping blade is enough to bring them back to spec. Why on earth would it be plastic???

    As frustrating as this seems to be, you are of course right to be doing it now, and if past history is any indication, you WILL figure it out. Cooling flow failure -> head gasket failure -> water in cylinders -> scored cylinder linings -> engine in 200 pieces with “impossible to repair” on the shop bill. (Although I did end up getting a nicer engine out of that particular incident….)

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