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1987 Mako 251 fuel tank

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  • 1987 Mako 251 fuel tank

    Hey guys, just purchased my first mako. Boat is in amazing condition for its age, while looking it over with the owner we ran both motors for about 30 min with no issue!!! I got it home and started it for the family while we checked out our new/used boat. Now here's where it gets interesting. First the port side motor died but the starbrd side was still running... immediately I was thinking about fuel. Changed all filters on both motors (2012 Honda 130s). Then I drained the water separators and found nothing but water. I disconnected my fuel line to the motor and began using the primer bulb and open line end to fill up 30 GALLONS OF WATER! . There is no smell of fuel in the bilge, I'm lost as to what is going on.. so I have 3 questions, 1) I can't find a tank anywhere for this model. 2) can you just unscrew the section of floor where the tank is or does it have to all be reglassed?? 3) who would you recommend in MD to complete the tank replacement if I Decide not to??
    thx!!

  • #2
    Sorry to hear you found that much water and have to tackle this problem so soon after buying. Exact specs for that tank will be hard to find online. Maybe one of the guys on this site who have that boat can give some insight.

    One of the great features of Makos is the tank is not glassed into the floor. After moving th console out of the way, to gain access to the tank is really as simple as unscrewing the coffin lid.

    Relacing a tank is not a complicated job, that does not gurantee it will be easy. Sometimes the old tanks put up quite a fight when removing them. Your best bet to get the size right is to remove what you have and take those measurements to a tank builder. While you are at it you should replace everything related to the fuel system so you don't have to revisit a problem under the deck down the road.



    Current
    '76 Mako 25 w/ '03 300 Yamaha HPDI
    Previous
    '85 Mako 21B w/ '94 225 yamaha
    '73 Mako 19 w/ '96 112spl Evinrude
    Brick, NJ

    Comment


    • #3
      So I pulled the access for the sending unit, noticed the gasket was pretty "weathered". The foam on the tank was moist but not saturated. There was absolutely NO smell of gas at all which made me happy. I pumped the tank out, replaced the gasket and added to 60gph racor water fuel separators and replaced all 3 fuel filters on outboards. I added some aviation sealant a marine mechanic recommended to the outside of the sending unit gasket. I'm going to let that set up over night before adding fuel tomorrow to get the outboards going again. Regardless this winter I'm pulling the tank and re-doing the fuel lines, wiring etc. Thanks for your help!!

      Comment


      • #4
        Just a heads up the foam at the top is almost never wet. I replaced my tank 2 winters ago. No smell in the bilge, foam ontop was dry. When I removed the tank I had pinholes on the bottom of the tank, fully saturated foam on the bottom half and a few gallons of a fuel / water mix in the coffin box. I hope the bad gasket is all it is for you and you have a trouble free season! Based on the age of your boat that tank is nearing the end of its life expectancy.


        Current
        '76 Mako 25 w/ '03 300 Yamaha HPDI
        Previous
        '85 Mako 21B w/ '94 225 yamaha
        '73 Mako 19 w/ '96 112spl Evinrude
        Brick, NJ

        Comment


        • #5
          So I'm thinking the foam on top was wet because the coffin lid was not silicone or 5200'd in?? if you walk into a shed with a gas can you'll smell gas, just find it hard to believe if the tank was leaking that I wouldn't smell gas... not calling you a liar and I appreciate your feedback but gas is a pretty potent smell. I applied new silicone to all deck seams. Think that will help?

          Comment


          • #6
            Yes. Seal those seams and any penetrations thru the lid.

            In addition to the junction of the coffin lid and the deck, there are some other areas that water could drain onto the top of the tanks. In my 1978 Model 25, the two primary sources that I found are the rod holders and the junction of the cap with the hull. My cap was slightly separated from the hull in the vicinity of the spring line cleats and wash that rode up the side of the hull in rough seas would enter the bilge. Also, two of the factory rod holders and all the rod holders that I added did not have sealed bottoms. At first glance you might think that those sources would not feed water all the way over to the top of the tank. But, on my hull they did…the water seeped across the top of the foam all the way to the tank coffin.
            Some of the floatation foam installed at the factory is injected thru holes in the gunnel cap which are covered up with the step plates. As the foam expands up the inside of the hull it creates two channels. One is against the hull and the other against the liner. In my boat the water against the liner eventually reached the tank. I’m certain the source was the water that was trapped against the liner.

            This photo below is looking aft, taken from one of the access ports in the liner. Any water trapped in the channel on the left side will eventually follow the fill and vent lines to the tank.


            In the process the aluminum lines and couplings became corroded and deteriorated. The corrosion of my vent tube lines is shown below..


            And the corrosion on top of the tank.


            This was my experience on my hull. Maybe those conditions don’t exist on your hull since it was built later than mine, but this info might be some help to you as you move forward.
            Ole Joe
            Just floundering around
            White Hall, Maryland
            1978 Mako 25

            Comment


            • #7
              Yes fuel is a potent smell. However smells have a hard time traveling through foam. If its concentrated in the bottom of the coffin and encased in foam you may not smell it. Countless guys on this site had no warning signs of a leaking tank, only to remove their tank and found what it did.


              Current
              '76 Mako 25 w/ '03 300 Yamaha HPDI
              Previous
              '85 Mako 21B w/ '94 225 yamaha
              '73 Mako 19 w/ '96 112spl Evinrude
              Brick, NJ

              Comment


              • #8
                Originally posted by flounder View Post
                Yes. Seal those seams and any penetrations thru the lid.

                In addition to the junction of the coffin lid and the deck, there are some other areas that water could drain onto the top of the tanks. In my 1978 Model 25, the two primary sources that I found are the rod holders and the junction of the cap with the hull. My cap was slightly separated from the hull in the vicinity of the spring line cleats and wash that rode up the side of the hull in rough seas would enter the bilge. Also, two of the factory rod holders and all the rod holders that I added did not have sealed bottoms. At first glance you might think that those sources would not feed water all the way over to the top of the tank. But, on my hull they did…the water seeped across the top of the foam all the way to the tank coffin.
                Some of the floatation foam installed at the factory is injected thru holes in the gunnel cap which are covered up with the step plates. As the foam expands up the inside of the hull it creates two channels. One is against the hull and the other against the liner. In my boat the water against the liner eventually reached the tank. I’m certain the source was the water that was trapped against the liner.

                This photo below is looking aft, taken from one of the access ports in the liner. Any water trapped in the channel on the left side will eventually follow the fill and vent lines to the tank.


                In the process the aluminum lines and couplings became corroded and deteriorated. The corrosion of my vent tube lines is shown below..


                And the corrosion on top of the tank.


                This was my experience on my hull. Maybe those conditions don’t exist on your hull since it was built later than mine, but this info might be some help to you as you move forward.
                So I sealed everything up that could be sealed with silicone. Dumped a half gallon of heet in the tank just in case I didn't get all of the water and installed 2 new racor fuel water separators. Went and fueled up then took the long bumpy way home! Both engines fired and ran flawlessly for about 2 hours. After running I attempted to drain the separators.... no water so far!!! Fingers crossed sealing the deck seams works because I've got that cbbt cobia and drum itch for next week.

                Comment


                • #9
                  Originally posted by fandarr View Post
                  Yes fuel is a potent smell. However smells have a hard time traveling through foam. If its concentrated in the bottom of the coffin and encased in foam you may not smell it. Countless guys on this site had no warning signs of a leaking tank, only to remove their tank and found what it did.
                  So if it was in the bottom of the coffin would that water drain into the bilge area??

                  Comment


                  • #10
                    Luke,

                    It might not "drain" into the bilge, but it should "seep" back there as long as the rear coffin bulkhead has a drain penetration. On the older 25s there is a PVC drain pipe through the bulkhead that extends halfway to the transom. So, if you have have the bulkhead drain, and if your tank is leaking, and if the gas is seeping to the bottom of the coffin, it should eventually show up back there. And as fandarr said you would smell it if you've got a gas leak. And, that would be true even if the gas was not visable of the bilge water.

                    But, we've gotten away from the problem that caused you initial post which was water in the tank. It's hard to imagine 30 gallons of water seeping into the tank past a "weathered" sending unit gasket. If the o-ring on your gas cap is missing, that could be another entry point. But again, it is hard to imagine that condition produced 30 gallons. I can't imagine a source other than a water hose feeding water directly into the tank.. Could someone accidently or intentionally put water in there?
                    Ole Joe
                    Just floundering around
                    White Hall, Maryland
                    1978 Mako 25

                    Comment


                    • Luke2016
                      Luke2016 commented
                      Editing a comment
                      The boat sat for 2 years. I think in between snow, rain and phase separation of ethanol fuel its definitely possible.

                  • #11
                    Last summer the float switch failed on my bilge pump and we had a nasty thunderstorm. I ended up with 6 inches of water in my boat for ~ 16 hours before I was notified by my neighbor (many thanks to him) that there was a problem. In that time I ended up with over 10 gallons of water in the tank, the only penetration point I could find was the sending unit. I never had a problem with water before that and have been keeping a close eye on the water separators and haven't had a problem since. So I would say that if water sat in it for some time (or if it sank) you could get 30 gallons just seeping through the sending unit gasket and screw holes.

                    I would just keep an eye on the separators and pay attention the next time it rains to see if anything happens.

                    Comment

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