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Thread: Boat mechanics input needed

  1. #1
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    Default Boat mechanics input needed

    OK kids, I have a small problem with a Volvo Penta 5.0 engine in my boat.

    Last week it overheated,(+210 degrees F) this due to a bad impeller on the raw water pump.

    This has now been replaced, but the engine still overheated after the replacement impeller was installed.

    So out of the water it came, after looking at the thermostat I found small bits of the old impeller inside the housing, so I cleaned out the housing, and back in the water it went, it still over heated, though not as bad,(under +200 F) out it came again, this time I looked at the main circulating water pump, found nothing, and tested it, it worked fine.

    So, I pulled all hoses and did a thorough cleaning, then a complete back flush of the engine block with the water pumps, and thermostat housing off the block, I made adapters to block off the one side of the water pump and one to push water through the thermostat entrance, this was a backwards flow, ran the water at street pressure for 10 min, I didn't see anything come out the discharge tube into the 5 gallon bucket I used to catch anything if there was anything blocking the water passages.

    I tested the thermostat by boiling it in a pot of water, it opened right at 167 degrees F, and was fully open at 174 degrees F, so it's not the problem.

    I tested the thermostat water sensor buy using an ohm meter and a pot of water on the stove, this along with a calibrated digital thermometer gave my the resistance readings for a wide range of water temp's, I know now that at 210 degrees I will have 64 ohms at the sender, and around 760 ohms at 70 degrees.

    This way I can tell directly at the engine if the water temp gauge is right or not.

    Now......Is there a filter somewhere that I am not seeing???? And if it still overheats after all this do I need to pull the heads to look for blockage?? (Not a job I'm looking forward too)

    This is looking to be a big project, I don't want to take it in to the service center as that is a bit above my budget right now, any advice from you boat guys will help.
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



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    Was the impellar broken up and did you find pieces if so. What was the flow of the discharge water like, after coming up to temp.

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  4. #3
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    The impeller was broken and also melted, (due to over heating) I found pieces in the main water distribution manifold, these have been removed and a new impeller installed, but after the thermostat opened the engine temp shot up to 200 degrees F, getting good flow from the raw water pump as the exhaust manifolds are just warm to the touch..

    Thermostat was removed and tested, it opens fine at around 165 degrees F, and is fully open at 170.
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



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    Possible that the impellar installed is backwards. Heard conflicting stories about whether they will self correct.

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    It will work both ways as it is the fin type, but it will only go in one way (indent on one side, see photo) because of the way the internals of pump body are setup.

    41atQEPblLL.jpg
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



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    The raw pump just cools external parts does it not? Things like the power steering and fuel.If thats the case i can't see this as the reason for it to over heat.The main pump on the front of the motor actually cools the motor.Can you tell if your missing any big pieces of the raw pump impeller? then again they would have to travel through small hoses so i can't see them plugging up the most of the water jackets for it to over heat.Kinda sounds like you maybe had a overheating problem which took out the raw pump.Only leaves few things in my mind to cause this a cracked head a thermostat or the main pump.I don't know if i'm making any sense here i'm just rambling.

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    Do you have an internal water system or straight raw water? If it is an internal system the exchanger may be partially plugged with impeller pieces.

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    Straight raw water system, no exchanger as I never plan to take it out in the Ocean.
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



    Coming soon to a crop circle near you.....

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    it was put in backwards.

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    Quote Originally Posted by hammer51 View Post
    it was put in backwards.
    See my number 5 post..........
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



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    gee isnt that a jabsco water pump? if it is still running hot then take a real good look at the intake port and its piping, it might have some sort of restriction you overlooked, that may have been why the other one failed,

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  17. #12
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    had a customer running a Volvo Penta with similar problem , if he just trolled slow it run warm but as soon as he got into the RPMS it ran hot . turned out to be the o ring around the water tube in the out drive , replaced it now runs cool at any speed
    PLEASE Do NOT PM me for support! Post ALL Support questions in the forums for all members to benefit.

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  19. #13
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    Ahhh sorry guys that I haven't been back to this one.

    I found the problem, it was a melted wire harness in the back of the engine, two wires in this harness were fused together possibly when it first over heated, the one wire was for the temperature sender to the gauge, it barely touching to the wire used for the over temp alarm, this caused a higher then normal reading at the temp gauge.

    I found this when I removed the back bulkheads for further testing, we tested it with a laser heat sensor gun, the engine was at normal temps, the gauge was at 200+, after the engine cooled, I looked all over it, looking for a plugged hose in the back, (there were none) that's when I found the melted wire harness, it was touching the exhaust manifold, and had melted when the engine first overheated.

    The replacement of the raw water pump fixed the overheating problems, but the fused wires gave a false reading at the instrument panel.

    I would have never found the problem if I hadn't removed the back bulkheads for the thermal tests.

    All works great now, the temp is back to normal. (170 degrees F)

    Thanks for all the help guys.
    ♫♫♫ I知 a lumberjack and I知 OK ♫♫♫ I drink all night and sleep all day. ♫♫♫



    Coming soon to a crop circle near you.....

    There is a 66 and third % chance that I'm on the right planet...

    "I'm happier then a Jackalope in a balloon factory"

    "First rule of testing satellites"
    "If its working fine now, then don't mess with it"

    "Second rule of testing satellites"
    "If you did mess with it, and now it doesn't work, can you blame someone else?"

    "Third rule of testing satellites"
    "If you did mess with it, and it doesn't work now, and you can't blame someone else"
    "Can you HIDE it"?

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