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2003 Mercury 25 intermittent water flow

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  • 2003 Mercury 25 intermittent water flow

    I just got a used 2003 25 HP long shaft Mercury outboard that will take a few minutes for water to start coming out of the water pump indicator.It is then intermittent and when it starts to flow again after a 45-60 second pause its very hot water coming out.This cycle constantly repeats.Water pump ? a blockage ? I have no idea when the impeller was replaced and I don't think its ever been replaced because the motor is pretty new and was in storage for a while.
    Thanks in advance !


  • #2
    Re: 2003 Mercury 25 intermittent water flow

    If it has been in storage the impeller may have dry rott. My mariner 115 did something similar. Then I replaced the impeller and it solved my problem

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    • #3
      Re: 2003 Mercury 25 intermittent water flow

      Mat2002 Welcome To Iboats I Would Change Impeller For Piece Of Mind
      Older enough to know better,young enough not to care--- Ladyfish

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      • #4
        Re: 2003 Mercury 25 intermittent water flow

        Thanks for the replys.What do you think of Sierra parts as compared to Mercury parts.I'm in East Quogue , Long Island , NY , USA.

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        • #5
          Re: 2003 Mercury 25 intermittent water flow

          IMHO i would get merc parts try dougrussell.com for parts and prices cheaper parts are not always better
          Older enough to know better,young enough not to care--- Ladyfish

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          • #6
            Re: 2003 Mercury 25 intermittent water flow

            Got the water pump kit from a local dealer.The old impeller was fine.I put in the new one with the other parts that came with the kit and guess what ?
            Still have the same problem. Any other ideas ? Thermostat ?

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            • #7
              Re: 2003 Mercury 25 intermittent water flow

              My 98 25 Mariner does the same thing..it trickles a bit inbetween the thermostat opening and closing though. The water is pretty hot but it's not boiling hot and I can hold my hand in it. Check your head temp by seeing if you can hold your hand on it for a while when it's running.

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              • #8
                Re: 2003 Mercury 25 intermittent water flow

                I have a 03 mercury tracker 25 hp long shaft. When first started it will take a couple of minutes before water starts to flow out of the tale tale spout. This is normal, the thermastat is cycling. You can pull out one of the pressure tap plugs in the cylinder head and hook up a cheap temp gauge to monitor temp. On your engine at wot what rpm are you getting? The reason I ask is that since new, my engine would only hit 4200 rpm. Pushes my 10 foot invader around 21-25mph. Mercury only makes 1 prop for this motor. If I rev it out of the water it will rev way past the 4200 mark.
                Monterey 206 br

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                • #9
                  Re: 2003 Mercury 25 intermittent water flow

                  I get 26mph with mine on a 1750 modV jonboat. I have four props for mine..one is a comp prop that is 15 pitch, the stock 13 pitch,a merc 12 pitch and a 9 1/2 pitch that I use when the boat is loaded to the gills for ducks. I use the comp prop 99% of the time cause it is the smoothest running of the four. Sounds like you need to lower your pitch to get the rpms up a bit.

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                  • #10
                    Re: 2003 Mercury 25 intermittent water flow

                    It was the thermostat.

                    Comment



                    • #11
                      Re: 2003 Mercury 25 intermittent water flow

                      I'm having the same issue - was the thermostat clogged? Were you able to replace it yourself? if so, how hard was it to replace?

                      Thanks

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                      • #12
                        Re: 2003 Mercury 25 intermittent water flow

                        The thermostats on these motors get clogged with sand pretty easily. Very easy to replace but you will need the kit with the new gasket. They also sell stainless steel replacement thermstats. That's what I plan to put in next time around as the brass ones seem to corrode. Also check your poppit valve if you have one (usually next to the thermostat). The rubber on mine deteriorated and also needed replacement.

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                        • #13
                          Re: 2003 Mercury 25 intermittent water flow

                          I've read a number of posts and some guys say the changing stream out of the tell tale and hot water are normal. How do I tell if it is the thermostat. I just had a new impeller put on.

                          thanks

                          Comment



                          • #14
                            Re: 2003 Mercury 25 intermittent water flow

                            The water from the tell-tale should be luke warm- 80F or so depending on the ocean water temp. It should never be steaming. You need to open up the thermostat panel to check if it the thermostat is clogged/ broken. You can take out the thermostat, put it in a pot of water on the stove and it should open up at the thermostat temp (mine is 143 F).

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