The honest answer to how often you should service a marine diesel is: whichever comes first, hours or calendar. UK cruising boats almost always hit the calendar interval before they hit the hours interval, and that is what catches people out.
The general rule
Most marine diesel manufacturers specify a full service every 200 to 250 hours, or every 12 months. On the Thames a typical leisure boat does 40 to 80 hours a season. That means you are almost always on the annual interval, not the hours one.
What manufacturers say
- Volvo Penta: 200 hours or 12 months for the main service.
- Yanmar: 250 hours or 12 months, with valve clearances every 500 hours.
- Beta Marine: 250 hours or 12 months, with the impeller inspected every season.
- Nanni: similar intervals, with closer attention to belt and pulley wear.
What a proper service includes
- Engine oil and oil filter, warmed first so the oil drains cleanly.
- Primary and secondary fuel filter change, plus a bleed of the system.
- Inspection of the raw water impeller, heat exchanger end caps, and exhaust elbow.
- Check of belts, hoses, mounts, anode in the heat exchanger, and gearbox oil.
- A written report with photos and a sea trial to confirm the result.
Book a service at your mooring
Annual services are booked at your mooring on the Thames. No lift out required for a standard service, and you get the boat back ready to cruise the same day.
