How to care for your boat’s engine — part one
Engine guru Andrew Norton explains how to properly care for your boat’s engine to ensure it performs better for longer.
Regular maintenance is the key to engine longevity — just make sure you don’t take on more complex jobs without having a service manual handy or a fair idea of the process. That being said, if you’re up for it then the DIY option is always a good idea. To give you the full engine maintenance rundown from Andrew, we had to break this rather lengthy piece into two. Read on for Part One and look out for Part Two which will be published next week.
Basically, there are three types of marine engines: outboards, sterndrives and inboards. Before undertaking any maintenance work, it’s important to establish your engine type and its specific parameters.
Outboards
Outboard engines are located on the outside of a vessel and come as either two- or four-stroke. The sale of new carburetted two-stroke outboards was banned in Australia at the beginning of 2019, so we will focus on four-stroke outboards. Four-stroke outboards function like car engines, where every fourth piston stroke is a power stroke. Four-stroke outboards also require more maintenance and until recently, most were relatively heavy for output. To reduce this weight, manufacturers have been opting for plastic air intake manifolds and EFI (Electronic Fuel Injection) down to 15hp. EFI is recommended with four-strokes as you can enjoy benefits such as smoother running, better throttle response and more power and torque per cubic centimetre.
Sterndrives
Introduced by Volvo Penta in 1959, followed by Mercury in 1961, sterndrives were developed to provide greater horsepower than the outboards available at the time. There was no need for a rudder, as with inboards, because the whole unit could be pivoted for steering. Available sterndrives ranged from 100hp Volvo Penta car engines up to several hundred horsepower V8 GM and Ford engines. The weight is low in the hull compared to an outboard on the transom to give a lower centre of gravity and better stability. Overall, because sterndrive props operate parallel to the water surface underway, they provide better propulsive efficiency compared with inboards.
Inboards
As opposed to outboards where the engine is mounted outside the hull of the craft, an inboard motor is where the engine is enclosed within the hull of the vessel. Despite high shaft angles, inboards are better suited to boats being stored in the water, because the exposed components are just the shaft, prop and rudder, and not an aluminium drive unit. Inboards also allow the engine to be positioned amidships, normally under the saloon and clearing the cockpit of engine box encroachment which is a common in smaller sterndrive boats.
Flushing outboards
You’ll need:
- Suitable immersion drum or flushing muffs
- Attachment for flushing where cooling water intake is under anti-ventilation plate
- Non-leaking tap and hose to ensure no air bubbles reach cooling system
- Stopwatch or phone to check running time if you don’t wear a watch
There are a few simple things you can do to ensure your engine lives a long and healthy life, and one of the first should be flushing your outboards. Current model outboards are made of aluminium so should be freshwater flushed after every saltwater run. If this is not done, aluminium chloride crystals are formed from a reaction of hot water passing through cooling water passages with the aluminium construction. These can then clog the passages, leading to the engine overheating.
Most recent outboards of 15hp and above have provision for flushing the engine without needing to run it — using a garden hose and a simple attachment. However, older outboards won’t have this provision and need to be flushed as the engine is running. With small four-stroke outboards up to 6hp, a simple drum filled with freshwater will suffice, but larger outboards should be flushed with muffs or ears attached to the cooling water intakes in the leg beneath the anti-ventilation plate.
With the outboard in the drum or flushing muffs attached, turn on the tap and make sure water is flowing over the end of the drum or spurting from around the muffs. Start the engine and run it at fast idle in neutral only for at least 10 minutes. Afterwards, reduce engine rpm to idle and switch off the engine before turning off the tap.
Remember: If you have an older carbie two-stroke outboard, never run it out of fuel or the lack of oil in the engine may cause the piston rings to scuff the cylinder bores.
Changing engine oil (and filter)
You’ll need:
- Suitable type and viscosity of engine oil (plus a new filter)
- Correct box spanner for removing sump plug
- Oil filter wrench
- Container large enough to hold all of the used oil
- Spare sump plug washers
Outboards
Engine oil should be changed every 100 running hours or annually — whichever comes first. After ensuring you have the correct engine oil (manufacturer recommended type and viscosity), fit flushing muffs or place outboard in the drum. Turn on the water until it is squirting from around the muffs or overflowing from the drum, then start the engine. Run it at fast idle for around 10 minutes then switch off and turn off the tap. Removing flushing muffs or lift engine out of drum and mount it on a stand in a vertical position.
Remove oil filler cap and sump plug and let oil drain into a container large enough to hold all of it. When most of the oil has drained out, remove the oil filter using a suitable wrench/strap. Unwrap new filter and half fill it with fresh engine oil. Smear some of this on the filter gasket then screw in position (hand tighten only, excessive tightening may damage the gasket and attaching thread). Fit a new washer to the sump plug and screw it until it is firmly sealed. Refill the sump with fresh oil until the full mark is reached on the level dipstick.
Fit flushing muffs again or place the engine in a drum and turn on the tap until water is spurting from the muffs or overflowing the drum. Start the engine and run it for another 10 minutes, checking for any leaks around the sump plug or oil filter. Switch off the engine and turn off the tap. Remove engine from flushing drum and let it sit upright for at least an hour until it cools down. Check the dipstick level again and if needed, top up to the full mark, and you’re good to go.
Sterndrives and inboards
If your trailer boat with sterndrive has cooling water intakes on the leg, then flushing muffs can be attached and the same procedure followed as for outboards.
If your boat is on a mooring — whether sterndrive or inboard — start up the engine and fast idle it for 10 minutes, shut it off, then remove the oil filter cap and sump drain plug.
When the oil has almost completely drained out, remove the oil filter and unwrap the new one. Half fill it with fresh oil and smear some on the gasket before screwing in (again, hand tighten only).
Fit a new washer to the sump plug, screw it in and fill the sump until reaching full on the dipstick indicator level. Start the engine and fast idle it while checking for leaks around the sump plug washer and filter gasket. Switch off after 10 minutes, let the engine cool, then after an hour or so top up sump to the full mark on the dipstick.
Read on for part two!
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How to care for your boat's engine — part two