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81 Evinrude outboard. Water circulation issue

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  • 81 Evinrude outboard. Water circulation issue

    I purchased a 1981 25 HP outboard. The guy swapped out a long shaft and put on a short shaft. It seemed to run fine initially. It would pee properly in the tank, and when sitting at the dock, but had issues restarting after running a while. We thought it might be an electrical issue. After cooling down, it would usually start up again. Three times needing a tow back to the dock.
    When I took it back to him, he said it was overheated and my fault. While testing it I had run it in a can of about 18 inches of water. It was deep enough for the water intake to be submerged, but wouldn't pee. When I put it into a deeper barrel, the same depth as the functional waterline, it would pee. I noticed there is an additional hole higher up that lies about 1 1/2 inches below the waterline when on the transom. If water went in there, it would pee, if not...no circulation.
    I assume this is an added overflow or drain hole, but can not find pictures. I need to prove this guy sold me a motor that was not circulating properly. I believe that when running on th lake, this hole was not getting water due to hull displacement.

  • #2
    Water needs to be 6 inches above the pump when running in a barrel.. the pump is not self priming..

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    • #3
      It was deep enough for the water intake to be submerged, but wouldn't pee.
      Not deep enough, the water pump which is at the very top of the gearcase needs to be fully submerged so the seller was probably correct.

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      • #4
        .The guy did the mount onto the boat. Its a shallow 15 inch transom so he suggested turning it into a short shaft. Took it to the lake three times. All three times it would not re-start. The motor was obviously overheating before I ran any tests in a tub. Can anybody show me on a picture of where the water level needs to be?
        What is the name/function of that hole that is on the forward side of the shaft. its about 6 inches below the bolt line of the engine head.

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        • #5

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          • #6
            This isn't the same motor, but similar, and my bucket was even deeper than this. Cavitation plate was always about 4-6 inches underwater. The hole I'm talking about is on the exhaust section.

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            • #7
              Water in the bucket shown above MUST be 8" higher.----A simple rule.

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              • #8
                Still doesn't address the fact that the motor was not circulating water when running out on the lake, but circulating when sitting at the dock. I can't seem to find any pictures with the hole in the exhaust housing that seemed to be the only place where the water was actually entering in from. Looks like this is not typical on other outboards.

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                • #9
                  The pump housing is sealed and gets water through the intakes and nowhere else.. Any holes you see are probably drain holes. If you ran it long enough without water you probably ruined the impeller. And maybe the motor also.

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                  • #10
                    I belive the main water intake is the screen in the snout behind the propeller.

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                    • #11
                      Originally posted by Wedge01 View Post
                      Still doesn't address the fact that the motor was not circulating water when running out on the lake, but circulating when sitting at the dock. I can't seem to find any pictures with the hole in the exhaust housing that seemed to be the only place where the water was actually entering in from. Looks like this is not typical on other outboards.
                      sounds like the intake below the plate might be clogged -- screen in that nose protruding in front of the prop. That is the primary intake when the boat is underway. There is also an intake just above the plate on one side of the housing, and that intake would draw some water at idle or when in reverse.

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                      • #12
                        Originally posted by racerone View Post
                        I belive the main water intake is the screen in the snout behind the propeller.
                        Yes your right. I was just trying to say that the water pump does not get water from holes in the EXHAUST housing.

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                        • #13
                          Wedge01-----I suggest you learn more about the way your motor works before operating it again.-----Talk to your local repair agent and ask how your motor works.-----Or learn through an empty wallet as has been done many , many times.

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                          • #14
                            http://ww2.iboats.com/Gearcase/dm/ca...iew_id.1548449

                            Might find this diagram useful to identify the intake screen down by the prop. Also note that the location of the impeller is at the joint between the exhaust leg and the gearcase. The water level needs to be substantially above that point.

                            If the screen is blocked, don't try to remove it unless it needs to be replaced -- particularly if this is a salt water motor. Use a small brad to clear blockages. Modern "muffs" don't work in flushing this motor, so you are on the right track in using a barrel. I recommend a plastic trash can, with the water level about half way up the leg of the motor. Run at idle or fast idle only.

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                            • #15
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                              Originally posted by Wedge01 View Post
                              .The guy did the mount onto the boat. Its a shallow 15 inch transom so he suggested turning it into a short shaft. Took it to the lake three times. All three times it would not re-start. The motor was obviously overheating before I ran any tests in a tub. Can anybody show me on a picture of where the water level needs to be?
                              What is the name/function of that hole that is on the forward side of the shaft. its about 6 inches below the bolt line of the engine head.
                              The picture attached shows the joint where the water pump is located. Water must cover it by several inches

                              I dont know about any hole on the forward side of the shaft 6" below the power head but the exhaust back pressure port is at about that height on the aft face of the exhaust housing. Also indicated in the picture.

                              A decent picture of your own engine would have made this explanation a lot easier to compile

                              Click image for larger version

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