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Boat engine won't start when warm

Does the engine start cold but not hot after a stop? It is usually flooded, either because the choke was pulled out or because you pumped the throttle. Otherwise it is the fuel, the spark plugs, a weak battery or a starter motor that loses power when it gets hot.

Check step by step

Select your engine on its model page to see the relevant steps and part numbers.

  1. DIY

    Outboards: start a warm engine without choke or fast idle.

    A warm engine doesn't need the choke. With the choke out or the fast idle lever up it gets too much petrol and won't start.

    Action: Push in the choke or lower the fast idle lever and try again. The owner's manual has a separate starting procedure for a warm engine.

  2. DIY

    Is the engine flooded? It smells of petrol. Let it cool and unscrew a spark plug. If the plug is wet with petrol, the engine is flooded.

    A flooded engine is most common when a warm engine won't start right after running.

    Action: Dry the plugs and refit them. Then start with the throttle fully open and the choke in, if that is how your engine should be started when flooded.

    spark plug
  3. DIY

    What petrol did you fill up with last? Check the octane rating, the ethanol content and how long it has been in the tank.

    The wrong octane rating and too much ethanol make hot starting harder. Petrol with alcohol can cause vapour lock, where the petrol boils in the hot fuel line and the engine gets only vapour.

    Action: Fill up with fresh petrol of the correct octane rating and no more than 10 % ethanol (E10). If the problem started after refuelling, drain the tank and refill it.

  4. DIY

    Drain the water separator under the fuel filter into a glass jar.

    Ethanol petrol absorbs moisture, and the water can separate from the petrol in the tank and be carried to the engine.

    Action: Drain or replace the filter. If there's a lot of water, drain the tank.

    fuel filterwater separator
  5. DIY

    Unscrew the spark plugs and check the electrode gap, deposits and cracks in the insulator.

    Worn, sooty or incorrectly gapped spark plugs give a weak spark, and it only shows once the engine is warm.

    Action: Brush them clean or replace them with the plug type and electrode gap the engine is specified for.

    spark plug
  6. DIY

    Does the starter motor turn the engine more slowly when it's warm? Test the battery and feel the cables.

    Heat increases the resistance in poor cables, and a starter motor with overheating damage gets weaker when it's warm.

    Action: Charge the battery, then brush and tighten the connections. If the starter motor still turns slowly when warm, have the workshop test it.

    starter motor
  7. Workshop

    Does the engine refuse to start when warm but start once it has cooled down? Then the ignition system needs to be tested at a workshop.

    The ignition coil and ignition module can cut out when they get hot and work again once they have cooled down. The same sometimes applies to the fuel pump.

    Action: Note how long the engine ran and how long it has to cool before it will start. The workshop can then test the parts while they are hot.

When to call a workshop

Call the workshop if the engine repeatedly refuses to start when warm despite the right starting procedure, fresh petrol and good spark plugs. The ignition coil, ignition module, fuel pump and starter motor are best tested warm.

Frequently asked questions

Why won't the boat engine start when it's warm?

Most often it has been flooded or the petrol is bad, with water or too much ethanol. After that come spark plugs, battery, cables and an overheated starter motor. If it refuses to start right after running, suspect the ignition coil or the ignition module.

The engine stops when it gets warm. Is it the same fault?

The cause is often the same: a closed tank vent, clogged filters, bad petrol or spark plugs. See the page on an engine that stops after a while.

Should I use the choke when the outboard is warm?

No. A warm engine is started with the choke in and the fast idle lever down. Using the choke on a warm engine floods it.

Can ethanol in petrol cause vapour lock in the boat engine?

Yes. Ethanol petrol boils more easily, and in a hot fuel line it can vaporise so the engine runs out of fuel. Volvo Penta petrol engines may use E10 at most.

Related troubleshooting

Sources

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