Problems cooling Yanmar 2GM15

Discussion in 'Diesel Engines' started by rd.sail, Aug 27, 2008.

  1. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    I have being having a problem with coolling my engine for about a year now. The engine stops pumping water (raw water) so it overheats. The problem only occurs after healing.

    I have had the technicians at my marina take a look at the problem 3 times. They check everything and they said it is fine. They lower the raw water filter. It seems to work but when I go out sailing and it is time to come back it stops pumping water.

    I have checked the water pump, change the impeller (which I do every year anyway). I have tested the pump when I have the problem buy disconnecting the exit hose and the pump is working.

    The last time the technician took a look at he said there might be a problem with the water heater going through the engine. Well, I took the water heater off the engine. It made it better but it still happens sometimes.

    One thing that seems to work, is when I start the engine I don't engage the transmission and I increase the RPM for a few seconds (15-30) and it eventually starts pumping water. If I don't do this it will not pump water through.

    Needless to say I have gotten very good at sailing in my boat into the slip.

    Does anyone have any suggestion or recommendations?
    Thank you, Daniel
  2. gramcko
    Joined: Aug 2008
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    Location: so cal

    gramcko New Member

    It's obvious a fuel saving feature. =)

    pump works
    impeller not being destroyed, so not sucking air
    so, flow is being restricted, but not by debris on the input side.

    my guesses: 1) old hose that is weak and collapsing. slows the flow until an RPM increase sucks harder. 2) salt build up. use Salt-away. then start fresh water flushing. 3) an impeller was destroyed and a piece is restricting the output side close to or in the heat exchanger (if you've got one, if not the engine).
  3. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    thank for the response gramcko.

    I have check all your suggestions. The first one I will try is the salt build up. The reason is that I have personally replace all the impellers in the past 4 years. They have all being OK with no need to change them but I do it anyway. As far as the hoses collapsing, I have check the and they all seam to be OK during the problem or when the engine in working correctly.

    As far as the raw water intake, I have check it cleaned everything form the through hole to the hose before the pump and did not find any obstructions.

    One question. Are there any valves in the system that might not be opening correctly?
  4. kenJ
    Joined: Jul 2005
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    Location: Williamsburg, VA

    kenJ Senior Member

    Is the intake hose positioned in such a way that it drains leaving an air bubble when healed? Might try closing the thru hull before sailing and see if it makes any difference. Also check your heat exhanger, pull the intake end cap off. I found that the previous owners of my boat were not so careful, must have had peices of 5 or 6 impellors blocking the flow. A bubble in the water heater loop will also cause overheat problems because it tends to slowly work it's way out. Pull both water heater hoses off the engine, poor anitfreeze into one end until it comes out the other, then reattach. I think older Yanmars also have a problem with the exhaust mixing elbow. The design slowly plugs up causing a lack of flow. Dirty job, but not too hard, might want to check that.
  5. rd.sail
    Joined: May 2007
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    rd.sail Junior Member

    ken J,

    thank you for the comments. I have not check the heat exchanger or the elbow. On your first comment. The intake hose, I reposition my whole intake system so that would not happen. Before the strainer was place high in relation to the pump and that was the first thing I tried.

    this is great I'm getting a list of things to check. I went out this weekend and everything worked great.
  6. Mychael
    Joined: Apr 2006
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    Location: Melbourne/Victoria/Australia.

    Mychael Mychael

    I'm not familiar with that particular motor so sorry if I'm giving you bad advice here.
    What can happen with the 2QM15 that I have is that if there has been slack maintenance in the past and the engine anodes are not replaced at the correct intervals then an anode can degrade to such a point that it basically falls apart and clogs up the water pathways in the head with a gluggy mess of old anode material.

  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Yanmar water pumps wear out and the impeller doesn't seal at the ends. It seems that they don't have much extra material. The solution is to either change the whole pump or take it out and machine some metal off the end so the cover fits tighter.
  8. rd.sail
    Joined: May 2007
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    rd.sail Junior Member


    Thanks for the reply. That is a very good solution. I believe the water pump is the original one which makes it 25+ years.

  9. paulhille
    Joined: Feb 2009
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    Location: northern nj

    paulhille Junior Member

    I don't know if this will help, I have a 38' with a Old renault 30 hp diesel, impellers went, I could not find any where. Mine was 2 impellers in I guess what you call a pump impeller chamber. I removed all impeller debris and installed what I call apump skid to the side of the inner engine compartment. It consists of a piece of 3/4" AZEK 20" longx 15" tall. AZEK is a type of plastisized wood. Anyway, I attached a 12 volt flojet pump,a matching flojet filter, a fuseblock. At raw water intake I now attach the hose to the filter,then the pump, then a hose to the inlet of the impeller chamber.I installed a lighting rocker switch and it was good to go. I was not sure how this would work, but, i have been using it for 2 years, water used to kind of drip out of my exhaust, now it really cools the engine. total cost around $150.00. I keep a spare pump and filter onboard. I have exact part #s if you need. Red
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