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OMC 15 hp 2 strokes overheating

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  • OMC 15 hp 2 strokes overheating

    I have had a few of these over the years overheat and stop running only to run again when cooled down. I'm sure this is not the only hp or brand that has done this. Does anyone know what exactly happens when outboards stop running like this?. They seize up but only til they cool down. Usually it is the water pump or blocked passages in the cooling system. Do the rings expand to cause this as seems logical? The motors usually seem to be fine and run again or maybe once in a while a blown head gasket is the only thing that happens.

  • #2
    the pistons expand to the point where they can no longer move in the bores. this usually also scuffs the pistons and bores.

    generally its not a good thing.

    keep the impeller in good shape
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      The piston rings and the piston top are as hot as they'll ever get due to the constant combustion action every (approximate) 11 seconds (idle rpm). As Scott states, it is the piston skirt area from top to bottom that expands in combination with the cylinder sleeve to a point whereas the piston has no clearance between it and the cylinder wall... and the piston can no longer move.

      One occurrence is enough to damage the pistons and also the cylinder wall.
      Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

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      • #4
        Couple an overheat with too low an oil mixture and pistons and bore become one in a welded THWACK!
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

        Comment


        • #5
          Ouch!

          After an overheating episode, it’s a good idea to replace the head gasket after resurfacing the head to correct any warpage. When addressing the cooling issue, you might consider replacing the upper water tube grommet in the inner exhaust tube at the powerhead. They can become deformed and block water flow. (i.e., If a new impeller/t. stat doesn’t fix the cooling problem, check the cooling passages for blockages when you have the cylinder head off. If still no success, consider the grommet — requires removal of the powerhead.)

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          • #6
            At idle the combustion process happens about 10 times every second , in each cylinder I would think.

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            • #7
              I think he meant ".11 seconds" or 11 times asecond
              '47 18' CC Utility "Knock On Wood"
              Various Evinrude powered Pontoons all named "Floosy"

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              • #8
                "due to the constant combustion action every (approximate) 11 seconds (idle rpm)." <--- Yeah... poor choice of words. That happens when I'm tired, overheated, sort of smashed, sick, overworked, and something else, can't remember.

                The above sounds like it fires once, coasts for 10 revolutions, fires again, etc etc...... Hey, remember those old cement mixers.... POW, fluh, fluh, fluh, fluh, fluh POW, fluh, fluh, fluh, fluh, fluh, etc etc.........

                Anyhow.... Should have been "due to the constant combustion action, 11 each second (idle 650 rpm)". Actually 10.833333....... but 10's okay by me racer.
                Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

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                • #9
                  Thanks for all the replies. I gathered the overheating was in the piston but narrowing it to the skirt makes a lot of sense since it is thinner metal than near the top of the piston and would expand easier I would think. Think I have been lucky so far with no head warpage I can detect yet anyway. Yes, For the first time I experience the dreaded water tube grommet problem on this 15 and replaced them. Have cleaned salt deposits before in other 15's, some so bad it was really a wonder the engine still functioned and did not overheat. What has been interesting the couple overheats in a few 15's I have had is that the paint never cooked off like I have seen in various other outboards. Any ideas why this did not happen? Was I just lucky it never reached that high of a temperature?

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                  • #10
                    You should take a coffee break and while you're at it.... buy a lottery ticket.
                    Our Questions Require Answers... If You Refuse To Answer Our Questions... How Can We Answer Yours?

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                    • #11
                      If you constantly have overheat issues, why are you not preventing them in the first place?
                      Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

                      1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

                      Past Boats
                      1970 Wooster Hellion - Merc 9.8
                      2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
                      1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

                      What’s behind you doesn’t matter.Enzo Ferrari

                      Comment


                      • #12
                        I thought it was usually cold in Alaska.-----So cooling system work is not that important.------The piston SKIRT is usually bigger in diameter than the piston near the rings.-----Therefor the skirt suffers first on severe overheat.

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                        • #13
                          If your boating is done in salt water on constant basis that OB needs to have exhaust, crankcase, thermo areas cleaned periodically by mechanical means no matter if OB is rinsed in fresh water or even vinegar for long time periods. Excessive salt formations will contribute to lessen the cooling effects of water passing by at pressure through entire powerhead.

                          When severe overheat occurs you can damage pistons, cylinders, warp head, melt cables among other issues. Know about this as have had 2 of those OB's. If wanting any OB to cool same as when out of the box must remove salt layers mechanically, once cleaned install new gaskets.

                          If your water pump its doing its homework right but all water passages works already with reduced diiam due to salt layers, crust, that OB is candidate to suffer repetitive overheats as described. So installing new impeller or entire water pump, thermo, water tubes it's no guarantee that will cure overheat issues. Who tears powerheads from time to time to make internal preventive maintenance ? No One..

                          Happy Boating




                          Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                          • #14
                            Yes, who tears powerheads indeed. I run in very shallow water at speed going over mud and weeds not in them like so-called mud motors do. Sometimes you will suck weeds and assorted mud into the engine plugging up the water pump, but not often I don't run in salt but have obtained outboards that have been. The water grommet issue is rare in my experience as after changing water pumps and/or impellers in dozens have only recently came across the water pump grommet problem that entails taking out the entire engine and a total pain in the badochie. I have had to resort to cleaning salt residue out of some and 1 had a half box of standard size Morton salt come out of the engine....and it still ran but hot. After cleaning and new impeller cooled like new. Thermostat problems are not that common in my experience either, but do happen. Taking the thermos out of the older 15's with the thermos on the bottom of the head is always a contorted problem. I always just take the head off to make life easier and the thermos easier to work on and remove and replace. Don't like the latter Mexico enchilada modular 15's. Poor design on the thermos me thinks.

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                            • #15
                              Sign up today
                              invest in some salt -away.

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