Honda 40 cooling mystery

Discussion in 'Outboards' started by Carlazzomark, Apr 28, 2022.

  1. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    Despite changing impeller, impeller housing and gaskets, a good thermostat, and making sure all lines are clear, I still do not have telltale output. I have placed a hose on the upper unit intake with the lower unit off, and the flow/telltale are fine. I have put the lower unit in a water tub and spun the shaft with a drill safely connected to the spline, and all is normal.

    What else could it be? How long can I run the engine without a telltale to warm up and test?

    Thanks
     
  2. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    Additional info: I took the thermostat out and ran the motor with the thermo cap off. No water here.

    So, having changed out the water pump system and tested the lower unit, and run hose water from the upper unit intake tube with success at the telltale, what am I missing? Is there a sensor before the thermostat port that could be bad?
     
  3. baeckmo
    Joined: Jun 2009
    Posts: 1,340
    Likes: 315, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    It seems the water does not pass from the pump into the intake tube leading upwards to the powerhead. You may not have got the tube to enter into the pump output recess or you have damaged the sealing collar.
     
    philSweet likes this.
  4. DogCavalry
    Joined: Sep 2019
    Posts: 2,135
    Likes: 1,078, Points: 113
    Location: Vancouver bc

    DogCavalry Soy Soylent Green: I can't believe it's not people

    There's a world, or rather, an engine worth of difference between "No telltale" and "No cooling water to engine" but the water path is very direct. As @baeckmo says, a connection is missing. If spinning the lower unit pumps water up hill, and directly pumping water into the power head also works, there's the location of your failure. Where the LU connects to the PH. There's no other available failure mode.

    In answer to your question, how long you can run it w/o water? A very short period of time.
     
  5. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    Thanks for you suggestion.
    Thanks. How would I check for that?
     
  6. baeckmo
    Joined: Jun 2009
    Posts: 1,340
    Likes: 315, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    ...."Thanks. How would I check for that?"...
    You have changed the impeller, according to your first post. For that, you removed the lower unit which holds the pump. Now when putting it together again, you must be careful so that the water tube fits into the pump outlet. On some engines the tube is easily displaced during the process; this is what I think has happened to your engine. Ergo; open the rig again and make shure the water tube is fitted correctly.
     
    DogCavalry likes this.
  7. DogCavalry
    Joined: Sep 2019
    Posts: 2,135
    Likes: 1,078, Points: 113
    Location: Vancouver bc

    DogCavalry Soy Soylent Green: I can't believe it's not people

    As @baeckmo says. The leg is easily removed. You can also put on a muff, feed it water from the tap, and crank it over in gear eithout fuel. Water should come out the telltale, the prop hub, and slots in the leg above the antiventilation plate.
     
  8. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member


    Now I am even more perplexed.this morning I took the lower unit off again, ran water into the upper unit again (telltale ok), and tested the lower unit in a tub again using a drill on the shaft. This time there was no water coming out the pump. Disassembled it, made sure the intake ports were clear, reassembled and tested. Same result, and all new impeller parts (housing, bowl, impeller). Put a second new impeller, and still the pump exit port is totally dry.

    wWhat am I missing or doing wrong?
     
  9. DogCavalry
    Joined: Sep 2019
    Posts: 2,135
    Likes: 1,078, Points: 113
    Location: Vancouver bc

    DogCavalry Soy Soylent Green: I can't believe it's not people

    Direction of rotation? If it's in reverse, but you're driving it forward judging by the prop, it won't pump.
     
  10. baeckmo
    Joined: Jun 2009
    Posts: 1,340
    Likes: 315, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Shaft key lost or old rubber pieces stuck in pump outlet?
     
  11. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    no, all fine here.
     
  12. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    When placing the housing over the impeller, I hand rotated the shaft clockwise to get the fins oriented properly, per a video I saw. Is this correct?
     
  13. baeckmo
    Joined: Jun 2009
    Posts: 1,340
    Likes: 315, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Yes, correct. You may try to "prime" the pump, ie pouring water into the delivery port before your bathtub exercise. If that gets the pump going, something is wrong/worn in the pumping department. Is it the correct impeller btw, check impeller width contra housing depth f.i. .
     
  14. Carlazzomark
    Joined: Oct 2006
    Posts: 100
    Likes: 13, Points: 18, Legacy Rep: 16
    Location: Michigan

    Carlazzomark Senior Member

    I have tried three different impellers and two different housings, so I don’t think that is the problem. If it were the case that the impeller was too large for the housing, wouldn’t the impeller be shredded by the torque of the motor?
     

  15. baeckmo
    Joined: Jun 2009
    Posts: 1,340
    Likes: 315, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Guess it's time for some pictures; till now we have been blind guessing.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.