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The boat engine knocks or makes strange noises

Trace knocking, ticking and vibration in the engine: oil level and oil pressure, temperature, belts, engine mounts, octane rating, valve clearance and injectors.

Check step by step

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

  1. DIY

    Find out where the noise is coming from: the engine block and belts, or the drive and gearbox. Listen with the engine in neutral and then with a gear engaged.

    Volvo Penta's GXi manual divides engine noise and vibration into engine components, ignition, cooling system, engine mounts and drive. Noise that is only heard with a gear engaged, or that comes from the drive, belongs on the drive side.

    Action: If the noise comes from the drive or gearbox: stop here and go to the troubleshooting guide for a knocking drive. Otherwise continue with the steps below.

  2. DIY

    Stop the engine, wait a moment and check the oil level on the dipstick. Also check whether the oil is dirty or milky.

    The GXi manual links valve knock (hydraulic valve lifters) to oil quality, quantity and type. The same checks are listed under the heading Low Oil Pressure or Engine Knock. Volvo Penta wants the oil level on the D1/D2 checked daily before the first start.

    Action: Top up with the oil specified in the manual, but never above max. If the oil is milky or is used up quickly: do not continue, contact a workshop.

  3. DIY

    If the oil pressure light comes on or the gauge shows low oil pressure: stop the engine immediately.

    Volvo Penta warns that continued running with too low oil pressure causes serious engine damage. The causes in the charts are low oil level, a clogged oil filter and, according to Vetus, also a faulty oil pump or a defective sender.

    Action: Check the oil level and replace a clogged oil filter. If the lamp stays on with the correct level: do not restart, have a workshop measure the oil pressure.

    oil filter
  4. DIY

    On diesel: read the temperature gauge. The D1/D2 table links engine knocking to too high coolant temperature.

    Volvo Penta's troubleshooting table cites excessive coolant temperature as a cause of engine knocking.

    Action: Reduce rpm and let the engine cool down. Go through the overheating troubleshooting before continuing.

  5. DIY

    With the engine off: check belts and pulleys. Look for wear, fraying, cracks and incorrect tension, and feel for play in the pulleys.

    The GXi manual lists loose belts and pulleys among the causes of engine noise. Vetus wants the V-belt checked every 500 hours, and Volvo Penta describes checking and replacing the belt on the D1/D2.

    Action: Tension or replace the belt according to the manual, always with the engine switched off. If a pulley or bearing has play: take it to a workshop.

    V-belt
  6. DIY

    If the engine vibrates at idle: inspect the engine mounts. Look for cracks in the rubber, loose bolts to the engine bed and mounts that have sagged.

    Defective engine mounts are in the D1/D2 table for vibration, together with an incorrect or damaged propeller. The GXi manual mentions loose, broken or worn mounts and loose bolts in the bed. According to Vetus, mount compression affects the alignment between engine and propeller shaft.

    Action: Tighten loose bolts. Have the workshop replace broken mounts and check the alignment.

  7. Workshop

    On petrol engines with pinging or knocking under load: check that the fuel has the correct octane rating.

    The GXi manual gives three causes of pinging or knocking in the ignition system: incorrect timing, corrosion in the distributor cap and rotor, and too low an octane rating.

    Action: Use the fuel specified in the manual. Have the workshop check the ignition timing, distributor cap and rotor.

  8. Workshop

    On a diesel with knocking or ticking despite the correct oil, temperature and mountings: have the workshop check the valve clearance and injectors according to the service schedule.

    Vetus schedules a valve clearance check every 500 hours on the M-Line and lists incorrect valve clearance and a faulty injector when the engine does not fire on all cylinders. Volvo Penta refers to its service protocol for service intervals.

    Action: The valve clearance is checked on a cold engine using the model's specifications. Have the workshop do it and test the injectors.

When to call a workshop

Call a workshop if the oil pressure is low with the correct oil level, if the knock gets worse with engine speed or if the oil is milky. Have the workshop check the valve clearance, injectors and alignment.

Frequently asked questions

Why does the engine knock on a cold start?

The manuals have no separate fault item for knocking at cold start. Check the oil level before starting and that the oil is the type and viscosity specified in the manual. On the GXi, valve noise is linked to oil quality, quantity and type. If the engine still makes noise when warm, or the oil pressure drops: stop it and have the workshop listen.

The engine knocks at idle. Can I keep running it?

First check the oil level, oil pressure and temperature. If the oil pressure lamp is lit, stop the engine: Volvo Penta warns of serious damage if operation continues. If oil, pressure and temperature are normal, the noise may come from belts, mounts or valve clearance.

Why does the engine vibrate at idle?

Volvo Penta's table points to defective engine mounts and an incorrect or damaged propeller. Look for cracked rubber dampers and loose bolts. Vetus points out that compressed mounts change the alignment between engine and shaft.

How can I tell whether the noise comes from the engine or the drive?

Listen with the engine in neutral and then in gear. Noises heard only in gear, or coming from the drive, belong to the drive side. Belts, mounts, oil and valves make noise in neutral as well.

Related troubleshooting

Sources

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