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25HP Mercury Change Impeller

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  • 25HP Mercury Change Impeller

    Ok, I went to sell my boat today and upon firing it up for a potential new owner, it wouldn't pump water. I vaguely remember getting into some sand with it on my last trip to the lake so I figure the impeller or water pump must be out. I've not changed this before but I've had the lower unit off of my Merc I/O and so I figured this would be the same. I have it in neutral and have pulled the bolts. It will drop about 1-2 inches and turn back and forth but sounds like its hooked up on the shift linkage or something. Am I missing a step here? It's a 1991 2 Cycle, 2 Cylinder 25HP long shaft outboard with electric start and the quicksilver remote steer/throttle.


  • #2
    Re: 25HP Mercury Change Impeller

    I have since discovered that this does not have a splined shift linkage and it moves the shaft up and down so it needs to be disconnected somewhere but I can find where to disconnect it.



    • #3
      Re: 25HP Mercury Change Impeller

      Check inside the powerhead, follow the shift linkage and I think there might be a quick-disconnect for the shift rod in there somewhere.

      p.s. if you sucked up a bunch of sand you may have gotten some lodged in the thermostat, so if you don't find anything wrong with the impeller, try pulling the thermostat cover and checking the 'stat out.



      • #4
        Re: 25HP Mercury Change Impeller

        Hey thanks for the reply. After inspecting I found that by pulling the starter I could get to the e-clip on top of the shift shaft to remove it. I hope those three words can save someone else a lot of time. Anyway, I don't really know what a bad impeller looks like so I'm attaching some pictures of the current situation. My guess by looking is its not bad although one of the rubber prongs seems to be wanting to flip backwards. Where is the thermostat located that it could be covered with mud? I'm not getting any water flow, just airflow from where the water should be coming.


        • #5
          Re: 25HP Mercury Change Impeller

          Also, I have never checked this but, how long should it be running before you see water from the spit hole or whatever its called, if it has a thermostat. I've always noticed it working before but don't remember if it spewed water from the moment I started it or not. Today when I fired it up from cold and it wasn't spewing any water from the hole, we both assumed it just wasn't pumping water, but I only let it run for maybe a minute before shutting it down. I didn't think you could run it for very long if it wasn't spitting water from the hole.


          • #6
            Re: 25HP Mercury Change Impeller

            That impeller has seen better days, but it still should have pumped a small amount of water.

            Since you have the lower unit off, this would be a good opportunity to blow air up the water tube and/or hook up a hose to the tube and flow some water thru the motor. You'll get a good idea if it's plugged up or not.

            The thermostat, if there is one on your motor, is located on the water jacket cover at the rear of the block (it's not a cyl head on this model) and is under a smaller cover, with 2 screws holding it on.

            Can't tell without a Serial # whether you'd have one or not, looks like some do and some don't.

            At any rate, if there isn't a smaller cover back there near where the telltale hose connects to the block cover, you don't have one.

            If you do, pull the thermostat cover for inspection. Flush water thru the copper water supply tube with the cover off and you should get a strong flow thru the open hole.

            If the thermostat looks nasty, replace it. If it's clean, might be OK. You can test in a pot of hot water, suspend the 'stat along with a candy thermometer so that neither touches the sides or bottom of the pot.

            The 'stat should be fully open somewhere between 120-130 deg. If it's passing 140 deg and the 'stat isn't even showing signs of opening, it's shot.

            When you get the new impeller installed, fire off the engine in a bucket (or with flusher if you have that) and see if it'll pump water out the thermostat hole. A good check of water pumping action. Once you reinstall the 'stat let it idle while monitoring the temperature of the exhaust manifold (the big flat cover on the Port side of the motor). If it gets hot real fast, shut the motor down. It should be fairly cool and only get warm-ish gradually if at all.

            Anyway, between those 2 areas (impeller and thermostat) you should find your problem.

            One word of caution if you have a 'stat is to watch out for the cover screws. If they're tight and won't break loose with normal hand tool force, heat 'em up with a propane or MAPP torch to help bust them loose. You don't want to be drilling/tapping/helicoiling busted screws in an aluminum block. No fun at all !

            HTH & let us know how it turns out...........ed


            • #7
              Re: 25HP Mercury Change Impeller

              well I put it all back together this morning after making sure everything is clean. The impeller looked good enough to pump water for now without having to order parts and wait. I found the thermostat housing, removed it and there's no thermostat in it, just the housing so I'm gonna run it and watch for water being pumped up to the housing.


              • #8
                Re: 25HP Mercury Change Impeller

                Well, it is pumping fine now. I cleaned out the tubes and apparently something was plugged somewhere that got free'd up. Thanks for all the help.



                • #9
                  Re: 25HP Mercury Change Impeller

                  Hi, i have the same motor except mine is a 1995. I too have had the same problem with the shift linkage and waterpumping in question. When i first got the motor it would not pump water on the hose but it would submerged in water. I asked my local marine center and they said 15hp and 25hp mercury at the time had a themastat that keeps a very precise temp. degree in the block and will fluctuate by opening and closing to keep the engine at a certain degree. I had never hear of such thing but sure enough it takes a while to pump but eventually it opens and when it cools down it spits. Recently I have had a case of sputtering and spit like the carb is dirty but, at the sametime I feel it could be a cooling problem because I can't run wide open without it wanted to shut down. If i slow down then it runs fine. So today i started snoopin around the lower unit but then i could not figure out how to disconnect the shift linkage so here I am and I just read your post and now i know how. Also if you still have the motor besure you are extremely careful with those water jacket bolts or any of the stainless to aluminum bolts like the other guy said. I broke 2 off a month ago trying to inspect the themastat and sure enough i was drilling and retapping in extremely nerve rakin places.


                  • #10
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                    Re: 25HP Mercury Change Impeller

                    im trying to do the same and i have a question i just took off the starter on mine and i saw the pin and removed it but the bottem didnt drop is there a reverse actuator philips screw to take off