When it comes to maintaining boat engines, the task can be as simple or as complicated as you make it. As a skipper, your relationship with that oil-filled pump lurking in the shadows could be as detached as having total reliance on the nearest engineer, or it could be as involved as digging out your tools and conducting a strip-down and rebuild.

Most of us would likely be satisfied falling somewhere between those two extremes – perhaps offering a bit of day-to-day care, but reluctant to take on anything major. But what sort of care are we referring to? What exactly does it entail and how frequently should we fulfil those tasks?

In most parts of the world, boating is a seasonal pursuit, with alternating periods of activity and dormancy. There are also lifespans on many of the components of an engine – lubricating oils become contaminated, filters clog, anodes waste away, and so on.

What you need is a schedule.

Basic maintenance intervals

Daily when in use

• Check fuel level
• Check crankcase oil lever
• Check freshwater coolant level. Remember that it’s extremely dangerous to open the header tank while it’s still hot
• Conduct a general check for leakage of oil, fuel or water 

Weekly when in use 

• Check belt tensions and inspect for damage
• Check gearbox oil level
• Check for water or sediment in the fuel tank. Inspect the prefilter bowl or drain off a sample from the bottom of the tank
• Check raw water strainer and clear it necessary
• Check battery electrolyte levels and top up if low 

Annually

• Check cooling system anodes, replacing as necessary
• Closely inspect all hoses for cracking, bulging or other signs of deterioration
• Check all hose clips for tightness
• Check the air filter, wash or replace as appropriate
• Check the exhaust elbow for corrosion. Ideally, you should detach the exhaust so you can have a look inside (exhaust elbows are a common source of trouble)
• Check engine mounts for deterioration. Look for loose fastenings and separation between rubber and metal components
• Check the shaft coupling and make sure all bolts are properly tightened

As recommended by the engine manufacturer

Certain jobs relate to engine hours and can arise at any time, depending on how much the boat is used. You should refer to your engine manual for the precise details, but the following are typical.

• Oil and oil filters should be changed every 100 to 150 operational hours or at the end of each season, whichever comes first
• Gearbox oil (or transmission fluid) should also be changed every 150 fours or annually, whichever comes first
• Replace fuel filters every 300 hours
• Saildrive diaphragms should be replaced after 7 years

Scheduled by the seasons

The reality is that most of us shuttle our maintenance plans to the calendar, and there's usually no reason why not. The average sailing yacht will spend only about 50 hours per year under power and even a motor cruiser would be pushed to make 150.

The all-important oil changes can therefore be scheduled as an annual event, and the time to start is when your boat is being put to bed for the winter. That way, the acids that are produced as a by-product of combustion won't be left to eat away at metal surfaces over the lay-up period. The other advantage of giving the engine a good going over in the autumn is that it leaves you plenty of time to rectify any problems you discover.

Some boats are laid up ashore while others remain afloat. It follows that jobs that might be possible in one situation won’t be in the other. Do what you can.

Once spring has sprung

• Check oil levels and top up if necessary
• Check freshwater coolant and top up if necessary
• Refit pump impeller
• Unseal any openings you might have plugged in the autumn
• Re-tighten all belts
• Reconnect batteries
• Cheer stem gland lubrication. Give the remote greaser a couple of turns
• Start the engine
• Enjoy!

RYA Boat Maintenance Handbook

Discover more about how to maintain your diesel engine in chapter 15 of the RYA Boat Maintenance Handbook.

This essential guide from boat maintenance guru Andrew Simpson is a must have for all marine enthusiasts and professionals. Packed with essential tips for effective boat care, maintenance procedures, troubleshooting, and safety guidelines.