How to Get a Yanmar 12HP Marine Engine to Start

Written by robert osborne
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The Yanmar 12HP, or horsepower, marine diesel is a one-cylinder, raw water-cooled engine in the YS model series. Yanmar marine diesels are very reliable engines that often give years of trouble-free service. You experience frustration when the engine does fail to start. Fortunately, you can easily fix the starting problem if you had operated the engine recently. A diesel engine needs only clean air, clean fuel and good cylinder compression to start and run normally.

Skill level:

Things you need

  • Hair dryer
  • Volt-ohm meter
  • Metric open end wrench set

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  1. 1

    Turn the engine's fuel shut-off valve to the "ON" position.

  2. 2

    Open the engine's seawater intake through-hull.

  3. 3

    Switch the engine start battery switch to "ON".

  4. 4

    Preheat a cold engine with a portable space heater or hair dryer. Aim the heat at the cylinder head. Ensure that you do not melt any wires or hoses.

  5. 5

    Engage the engine's starter by pressing the "START" button. The engine should turn over. If the engine does not turn over, measure the voltage at the battery with a volt-ohm meter set to the DC Voltage scale. The reading should be 12.5 volts. If the reading is lower, charge that battery with a battery charger. Try to start the engine again. If the battery reads about 12.5 volts, the problem may be with the starter or a loose connection.

  6. 6

    Confirm that the battery and starter connections are tight and corrosion free. Clean off any corrosion with a wire brush or sandpaper. Measure the voltage at the engine starter solenoid. The starter--solenoid is faulty if the reading is 12.5 volts and the engine still does not turn over.

  7. 7

    Remove and inspect the engine air filter. Ensure that the filter is clean and is able to pass air to the engine.

  8. 8

    Inspect the engine fuel filter's sight bowl. Confirm that there is no dirt or water in the bowl. Replace the fuel filter if dirt or water is found. Clean diesel fuel is straw coloured.

  9. 9

    Loosen the fuel line at the engine's injector with an open-end wrench. Crank the engine over with the starter button until a steady flow of fuel is seen without any air bubbles. This procedure is known as "bleeding the fuel lines." Re-tighten the line at the injector.

  10. 10

    Press the "START" button. The Yanmar engine should start and run at idle speed. If the engine still fails to start, the problem is an internal mechanical problem. You must contact a marine diesel engine mechanic.

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