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  1. #1

    Default 8v-53 overheat at idle ok running

    Hi all,
    I have a pair of 8-53 and one is overheating in gear at idle, if I increase rpm it immediately cools down to 150.
    It is keel cooled aluminum boat,we have flushed coolers and engine several times, replaced thermostats replaced water pump.
    recently we replaced cracked head then started having this problem.
    Also getting oil in cooling water and air out of bleeders on top of stat housings.
    I am wondering if head install might have gone wrong and is introducing combustion gas into coolant and causing air lock at low rpm?
    I make my living with this boat and am at my wits end.
    This engine has allways run at 150 up to around 1400 rpm and at 2350 cruise speed 175-180. Other engine runs normal temps.
    Any thoughts?

    Thanks

  2. #2
    Join Date
    May 2015
    Location
    Oregon
    Posts
    72

    Default Re: 8v-53 overheat at idle ok running

    Don't know 53s too well, but ran 6v53s a long time ago. Only 71s for 40 years. Oil in water, considering head change could be head gasket. That also could put combustion air into the water causing air in the water system. If there's a lot of air, it could stop water moving. Air instead of water around the thermostat can keep it closed. On some other diesels without a thermostat bypass line I sometimes drill a 1/16" hole in the stat to stop air locking when replacing coolant.
    I would do a compression check. Then pressure test the oil cooler/heat exchangers. If the replacement head was used, pressure check it.
    Try boatdiesel.com. Lotta Detroit mechanics there.

  3. #3
    Join Date
    May 2015
    Location
    Oregon
    Posts
    72

    Default Re: 8v-53 overheat at idle ok running

    I should have said to check each exhaust port with a hand temperature gun to see if all cylinders are running the same. A low temp port could mean low compression, head gasket, etc.

  4. #4

    Default Re: 8v-53 overheat at idle ok running

    I did ck exhaust port temps and they seem consistent.

    The water temps have stabilized lately but too cool at 165 running and not getting hot at idle. I have thought of drilling steam holes in thermostats to keep a little water moving thru keel coolers.
    I plan on compression check soon maybe that will tell something. Still getting small amount (1-2 seconds) of air from bleeders above stat housings.
    Thanks

  5. #5
    Join Date
    May 2015
    Location
    Oregon
    Posts
    72

    Default Re: 8v-53 overheat at idle ok running

    On auto and small diesels, I always do a small hole in the thermostat. It helps in initial filling and stops any air lock. All Detroits I used had a bypass for minimal flow when cold. Usually when the engine won't warm up at idle, it's a stuck open thermostat. But my Detroit experience is all heat exchanger engines. On keel cooled engines I have run in cold weather, often won't warm up all the way until under a load. Sitting at a dock with no flow past the boat, the engines get too warm. I assume the water around the tubes gets warm and isn't moved away.

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