Dennison Berwick gives you a complete guide to getting you boat engine fired up and ready for the new season

Preventative maintenance is the key to enjoying summer on the water and avoiding breakdowns. Credit: Alamy

Getting the boat engine ready for service after lay-up (sometimes called ‘summerising’ in contrast to ‘winterising’) should be straightforward and not difficult or time consuming, especially if some of the necessary tasks were completed during laying-up, writes Dennison Berwick.

If these tasks (such as oil change and impeller inspection) were not completed, now is the time – before an engine breakdown spoils time on the water.

It is goof practice to change the oil filter whenever you change the oil

Preventative maintenance is the key to reliability and well worth the modest investments of time, effort and cash.

When we think of our summer sailing it is rare we imagine ourselves motoring along but it is an absolutely essential piece of equipment to keep functioning well

Dennison Berwick is author of Marine Diesel Basics 1: Maintenance, Lay-up, Winter Protection, Tropical Storage, Spring Recommission (Voyage Press, £10.99) the first visual guide to marine diesel systems. He lives aboard SV Oceans Five, a 36ft Chevrier build in 1982

Keeping a maintenance log may sometimes feel like an extra chore, but having one greatly simplifies getting re-acquainted with the diesel system after months away from the boat – jobs done, items taken apart (such as raw water pump), tasks yet to be completed, and items removed from the boat.

A log is simple and easy to keep; don’t trust to memory for information on which the boat engine depends.

A double-page spread in a plain notebook works well.

It can feel like a big task but if it is something you get into the habit of filling out after any work it adds little to the time it takes to complete a task.

Before tackling specific tasks, it’s a good idea to use a strong light and take a look at the engine compartment, the engine and components, under and behind the engine, and in the bilge to ensure everything looks okay.

It’s surprising how much can be picked up by a glance:

Diesel boat engines need scrupulously clean fuel.

Any sediment or water in the fuel will have settled out during lay-up so it’s worthwhile draining a sample from the bottom of the fuel tank, if this is possible.

Abnormal water in the tank may indicate a leaking deck fill cap, maybe from a missing or damaged O-ring.

Growth of HUM (Hydrocarbon utilising microorganisms) is generally not a problem in colder climates, but can grow with alarming speed in hotter regions.

Adding a dose of biocide to each fuel fill can prevent a lot of trouble.

Abnormal water in the tank may indicate a leaking fuel cap

Best practice is to change the primary (off engine) filter every autumn and the secondary filter at least every second year, using 10-micron and 2-micron elements respectively.

Any water in the bottom of the primary filter should be drained before start-up.

It’s a common misconception that fuel is clean if it looks clean.

Human eyes can see down to about 30-40 microns in size. A grain of sand is about 100 microns and red blood cells 8 microns; so it’s not possible for naked eyes to see the particles that can eventually plug a 10-micron filter.

Best practice is to change both fuel filters at regular, fixed intervals, even if they look clean.

Don’t start a new season with old oil in the boat engine.

If this vital task was omitted during lay-up, the engine oil and filter should be changed now to remove corrosive acids, which attack the inside of the engine, and to help prevent carbon sludge building up and blocking small oil passages.

Change the primary filter ever autumn

It’s a good idea to also change the automatic transmission fluid (ATF) in the gearbox each year.

The ATF certainly should be changed if there’s any evidence of overheating (darkening of the fluid). Additives in the fluid break down over time and the gearbox works hard, so this is cheap insurance.

Gravity drains the engine oil into the sump throughout the months of lay-up, leaving bearings and surfaces exposed.

When you refill the oil, make sure the dipstick is properly seated for measuring so you don’t overfill. Remember to check and replace the gearbox oil too

Rather than immediately firing up the engine, it’s prudent to start the engine the first time in three steps to help distribute some oil over bearings before the metals heat up and expand:

A little dishwashing liquid on the vanes of the raw water impeller make it easier to twist and insert the impeller without cutting or nicking the rubber.

Check that the inside of the cover plate is very clean (use 240 grit paper for a light sanding, if necessary) and that the paper gasket or O-ring is in perfect condition.

Any small defect can seriously reduce the amount of water pumped.

It’s a good idea to leave changing the impeller to the spring, so it doesn’t have time to sit and harden in the engine over winter

Impellers on some engines can be hard to reach, discouraging removal and inspection.

However, it’s not possible to properly inspect for damage, such as small tears at the base of the vanes, when an impeller is compressed inside the pump housing.

Make sure you replace the gasket or O-ring on your water impeller. A tiny leak can stop it working. Credit: Graham Snook/Yachting Monthly

In addition, if the impeller was not removed during lay-up, some of the vanes will be permanently bent (‘taking a set’).

The pump will still function but will likely be less efficient.

The fluid should be changed every two years, preferably during lay-up, before precipitates have a chance to block small cooling passing in the engine block.

Check the level, either in the header tank or the overflow bottle.

Always pre-mix antifreeze/coolant and water to ensure full mixing before adding.

Diesels run best with lots of clean, cool, oxygen-rich air.

A boat engine burning one litre of diesel per hour needs about 15,000 litres of air (source: Baldwin Filters).

Good engine compartment ventilation also helps remove engine heat, providing cooler air to the engine intake.

It’s easy to forget to reopen any vents or to remove any insulation baffles installed before winter.

A battery showing 12.65 volts (fully charged) may still have reduced capacity due to sulphation during lay-up (hardening of sulphates on the battery plates).

This happens over time if a battery is not kept fully charged.

Load test your batteries if you have any doubt about their capacity. If the voltage drops below 10V while cranking then the battery may be on its last legs

Load test the battery if there’s any doubt about its capacity and ability to start the engine throughout the coming season.

A load tester typically puts a 10-amp load on a fully-charged battery and measures the voltage. If the voltage falls quickly or low (below 10 volts), the battery is likely to need replacing. The same test can be made with a multimeter measuring battery voltage while cranking the engine.

Galvanic corrosion (between dissimilar metals that are electrically connected by water, or antifreeze/coolant) continues even during lay-up, so all anodes should be rechecked and replaced when about 50% consumed.

This includes the anode on the propeller shaft anode, if the vessel was laid-up in the water.

Tim Bartlett explains how you can diagnose some common marine diesel engine problems, and fix most of them

Small four-stroke outboard engines are pretty simple. Max McHugh of Marine Matters explains how to fix the most common problems,…

E10 petrol, which contains up to 10% renewable ethanol, will be introduced as standard at petrol forecourts in the UK…

Duncan Kent examines the implications of switching from red to white diesel and what you can do to avoid fuel…

Not all boat engines have anodes (check the manual).

A heat exchanger can develop pin-prick holes if its protective anode is allowed to be consumed.

With the gearbox in neutral, the propeller shaft should turn easily and smoothly with little resistance.

And there should be little or no side to side, up and down movement of the shaft in the cutlass bearing (Cutless is a trademark).

Aligning the engine should not be necessary if no work was done on the drivetrain or engine mounts.

After an absence from the boat, it’s easy to forget a few items that should be checked just before and immediately after engine start up.

Using a checklist jog the memory and help make sure nothing is missed.

Inside the June 2022 issue of Yachting Monthly: Everything you…