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OMC 15 overheating revisited

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  • OMC 15 overheating revisited

    My other post concerning this got kind of hijacked with talk about salt water salt buildup. But, that's ok as it was all useful info. To delve a little further into this overheating question I might be so bold to ask at what stage of engine paint blister and burn off could one expect engine piston/ring damage to occur. This is probably technically not exactly possible but some old hands with lots of overheating of OMC outboard engines over the years just might have some real life hands on experience to relate. Also, I knew that piston/ring/cylinder damage was the most common damage from overheating, but damage to other vital engine components must occur also, like to bearing. Is there any kind of parameter one might use to predict or expect other vital engine damage beside that that goes on in the bore? I know that lugging engines is hard on bearing, but high engine heat must also be a major factor and of course some engines and bearing layout are tougher than others.

  • #2
    Haha yes you never know when a debate is going to light up on here, but i like them because as you say its all good info to know about. The longest one ive known of was one on the electronics of the oil/fuel VRO.
    Paint peeling is a sign to me to double check what i look for but i find you can overheat lose a lot of paint and have apparently no discernible damage.
    My main candidate for trouble in an overheat is a warped head, but those are easily fixed by planing on light sandpaper on a piece of glass or mirror.
    Next is the exhaust plates on the motor, if they get warped then on some models water can enter the cooling passage and pressurise the cooling system, ie restricting cooling water into the head etc. Ive seen it so bad that theres no water flow through the motor, the exhaust leak is large enough to counteract all the force of the impeller. Unfortunately you cant check for a small combustion leak in the cooling system like you can in a car.
    Bearings, ive never really had a problem with. Old main roller bearings were susceptible to failures from crud build up but the newer sleeve type one have never thrown in overheats ive worked on.
    Wrist pins seems to have some added protection from overheat failure probably from the inflow of air and fuel mix to the underside of the piston.
    The main times ive dealt with cylinder gouges its being from ring failure. To me those failures appear to be from the landing pin in the ring set moving in or out and the ring then turns and catches the edge of a inlet or outlet port. Or the ring grooves a so full of carboned up gunk that there is no movement (expansion and compression) allowed in the ring grooves and they thus prematurely wear and then snap.
    All just my personal observations, no sophisticated population sampling, just what ive seen at autopsy, but after being one involved in hijacking your last thread i thought id make some amends

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    • #3
      why not keep the impeller and cooling system maintained and prevent the over-heat to begin with.

      as for level of outward appearance during a catastrophic overheat. it will vary. there is no definitive level of outward damage to be able to assess internal carnage.

      any overheat is bad and causes internal damage. to what level is a case-by-case basis.

      I have taken engines apart that have had paint blistered and there was only light scoring. I have come across engines that have had no sign of overheat to find that they were run hot, and tore up the bores/pistons.

      best is to do the maintenance to prevent the over-heat 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

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      • #4
        Sorry to have highjacked the original post, but doing preventive maintenance say impeller or full water pump change along a new thermo will do nothing as excessive saltpeter building up issues will screw the entire equation....

        A short 2 strokes story : Going back to your 15 HP Evi model. As I sometimes liked going boating on kelp, algae waters and consequently the lower leg water intakes sucking them up to the point of literally melting the impeller inside its liner, warping cylinder head and even melting cables near crankcase due to running at high rpm when that scenario occured. Have had 0 issues with piston, piston rings and cylinder walls when OB was seized due to instant extreme heat building up.

        After replacing a new impeller, retorquing cylinder head, exhaust gaskets to fact torque specs the OB was brought back to immediate life, this scenario has happened 3 times not in a row though. LOL!! The use of good quality 2 strokes oil contributed to having 0 internal issue and not damaging the powerhead at all..

        Happy Boating


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

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        • #5
          Good info...thanks guys! Yes, I believe that synthetic oil helps prevent catastrophic damage a lot of times. I know some say no? Yes, even with good maintenance it is possible to get into foul bottoms and weeds etc.in some locals. It's reassuring to know that you won't lose the motor to destruction all the time. Now I can sleep at night lol

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          • #6
            Be aware that seizing any engine up due to an extreme overheat cond its a different story than when seizing same due to poor quality 2 strokes oil used or bad fuel/oil ratio mixture employed. In first scenario most times will be able to spring back to life any engine, on second one will have my doubts as too many internal parts will be highly compromised on engines seized while running at high rpm.

            Happy Boating


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

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            • #7
              Great post Sea Rider as I mostly think of overheating due to lack of cooling. Good to know that most times engines are not compromised. Makes a lot of sense as some oil present in overheating is better than no oil at all. Never have had any of those problems. Run small portable outboards most of the time so no multi-cylinders to mess with where that would be more prevalent. I know jet outboards run into a lot of those type of scenarios.

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              • #8
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                Worst scenario would be an extreme overheating condition along a ooops forgot to add 2 strokes oil to the fuel while running wot.

                Happy Boating


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

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