QD19 Overheat Question – Update

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  • beerman57


    Replies: 596
    Topics: 126
    #1830

    As you may know, I rebuilt the powerhead on my 1958 Johnson 10hp. The shift handle and upper midsection get hot, the mid hot enough to boil water. I can’t find anything wrong, nothing plugged up, pumps plenty of water. Running it on a hose, you could hold your hand on the cyl. head all day, never checked it on the boat after being up on plane. So my question is, what do you think of removing the plate (#2) in the diagram, to let the exhaust down the mid with less restriction. The plate is right in front of the water discharge hole in the mid and blocks off the exhaust cavity in the mid, directing the exhaust forward as it goes down, into the cavity with the shift linkage.

    http://www.marineengine.com/parts/johns … Lower+Unit


    chris-p


    Replies: 2456
    Topics: 153
    #18711

    I believe that plate doesn’t prevent gas from going DOWN, it actually prevents gas from coming back UP>

    If you remove it, and look down it, you will notice there is a port a couple inches down, into the chamber that the spent cooling water is diverted on its way out the snout.

    The exhaust gas come up the chamber that the plate covers, out through that bypass port, then out the snout with the spent cooling water. If that plate were removed, you would have excess build up of gas there with no where to go.

    I don’t totally understand the engineering of it, but I BELIEVE, that there is a siphon type effect that goes on there. Removing that plate would make it worse. Just my 2 cents. Wait till the mechanics chime in.


    fleetwin

    US Member - 2 Years
    Replies: 4737
    Topics: 46
    #18713

    Still waiting to get home to search around for a midsection/powerhead to look at dissect. But, I don’t think I would remove that plate.


    legendre


    Replies: 389
    Topics: 8
    #18716

    Certainly no expert here, but out of curiosity, how do the plugs look? Are there any signs of overheating, what does the mixture ring look like, etc..

    Point is, it sounds like you really don’t know what’s going on – as in, is this an issue of excessive heat production (incorrect ignition timing, mix too lean), or an issue of improper heat flow through and out of the engine (improper exhaust flow or weak cooling performance)?

    If the plugs are still new or very nearly new, they might not be able to provide enough info. If that’s the case, consider putting in a good, used set and run those for a while, to get a better read.


    beerman57


    Replies: 596
    Topics: 126
    #18726

    Plugs are dark, new impeller, wear plate & housing are in good condition. 9 hours of break-in on the motor, runs perfect for all 9 hours, not even one sneeze. Relief hole in the water discharge isn’t plugged up, snout in the gearcase either. 24:1 mixture (1 quart to 6 gals.). If the shift handle wasn’t hot (only at idle) or the upper, starboard mid wasn’t getting discolored, I wouldn’t know or probably even care.


    garry-in-michigan

    Lifetime Member
    Replies: 3583
    Topics: 31
    #18732

    It seems to me I saw a service bulletin about complaints of the paint turning brown under the powerhead. It seems to me the cure was to remove the powerhead and drill a 3/16" hole at an angle in a specific spot in the water jacket to cool the exhaust under the powerhead.
    Now I have to look through 600 service bulletins to find where to put the darn hole.
    … 🙄


    beerman57


    Replies: 596
    Topics: 126
    #18734

    This appeared to be a fairly low hour motor, but froze up from sitting after the top main seal developed a leak, ruining the crank but the conn. rods did have play.
    Garry, I’ll be more than than happy to pay you for your time, this DARN thing has me beat. Any way I can help you look for the bulletin from 60 miles away? Not that you would want me on your computer, but do you use "teamviewer"?


    chris-p


    Replies: 2456
    Topics: 153
    #18735

    Someone had posted a bunch of the service bulletins somewhere did they not?

    I have a few bulletins, but no where near 600!

    That is very interesting Garry! Thanks.

    Ill look through what I have as well


    jeff-register

    US Member - 2 Years
    Replies: 1562
    Topics: 54
    #18737

    Garry,
    Bless you!! I too have been trying to help Robert but as you know I know little about Johnsons. Would a bulletin be in my Johnson service manual? It is a older one with a red cover. As usual you have the correct reply. Does this bulletin appear in the older Evinrude manual as well? The 58 leg was a redesign using the 5/7.5 hp leg correct? Seems the cooling system would be smaller as well too. Thoughts?
    Thank you!!


    legendre


    Replies: 389
    Topics: 8
    #18739
    quote beerman57:

    Plugs are dark

    As you know, that tends to indicate a rich condition – but how dark are they?

    In any case, I’d suggest you rule out a rich mixture and/or retarded ignition timing. Not saying these are creating your issue, but IMO it’s imperative that you rule them out before going down any other avenues.

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