Boat engine service: inboard, outboard and diesel maintenance
Quick answer
Basic boat engine maintenance means changing oil and filters every 100–200 hours or once a year, replacing the raw-water pump impeller every 1–2 years, checking anodes, belts and coolant, and inspecting the fuel system. Doing it before the season prevents most breakdowns at sea.
What an annual engine service includes
- Engine oil and gearbox or drive oil change.
- Oil, fuel (plus water-separating pre-filter) and air filter replacement.
- New impeller in the raw-water pump.
- Inspection and replacement of heat-exchanger and engine anodes.
- Check belts, hoses, clamps and coolant.
- Batteries, alternator and electrical connections.
- Sea trial: temperature, oil pressure and exhaust.
Get the full printable list in our boat engine maintenance checklist.
Inboard, outboard and diesel
Outboards also need lower-unit oil checks, greasing and a freshwater flush after every use. Diesels are very reliable if fuel is clean: water in diesel is the number one cause of breakdowns. Find specialists in outboards or general mechanics.
Winterising
If the boat will sit idle for months, winterise it: oil change, fuel stabiliser, full tank to avoid condensation and cooling-system protection. It is all in our boat maintenance calendar.
Frequently asked questions
How often should boat engine oil be changed?
Every 100–200 running hours or at least once a year even with few hours, because oil degrades with time and moisture. Always check the manufacturer’s manual.
How often should the impeller be replaced?
Every 1–2 years, or sooner if vanes are cracked or deformed. A failed impeller can overheat the engine in minutes.
Engine service by port
Engine service: professionals by area
Related guides
Boat engine maintenance checklist before the season
The list marine mechanics use to prepare an engine for the season, adapted for inboards and outboards.
Boat maintenance calendar: what to do each season
A simple annual plan to keep your boat ready: what to check before, during and after the season.
Other maintenance services
Antifouling & haul-out
Antifouling is the paint applied below the waterline to stop algae, barnacles and other organisms sticking to the hull. In the Mediterranean it is usually renewed once a year during haul-out, when the bottom is also cleaned and anodes, propeller and through-hulls are checked.
View serviceBoat cleaning
Professional boat cleaning covers washing deck and hull with marine products, gentle teak cleaning without a pressure washer, rinsing stainless steel and cleaning interiors. The bottom can be cleaned in the water by a diver between haul-outs to keep performance up.
View service