2021 Mercury 15 EFI Fourstroke outboard engine review

However, it’s more than just an outboard engine, with some clever thinking going into how owners will use it.

The Mercury 15 EFI Fourstroke is designed for both tiller and forward control applications. For this test, the engine is mounted to an AnglaPro Core 374STL tinnie and steered via Mercury’s small engine tiller control.

Introduced in 2017, the Mercury 15 EFI Fourstroke is an in-line two-cylinder water cooled engine that uses an electronic ignition system so it does not need to be tethered to a battery.

Designed to be lightweight, the Mercury 15 EFI Fourstroke tips the scales at just 45kg dry in its lightest form, making it on par with other four-stroke rivals in this class. You can add more weight by opting for power-assisted tilt and trim if you’re using a forward control on something like a skeleton console RIB.

The low weight makes it easy to manually lift the Mercury 15 EFI Fourstroke for transport. Getting it up to the top position is a two-click process to get past the shallow water drive setting – more about that later.

The 15hp outboard engine shares its engine block and almost all its components with the 20 EFI Fourstroke, including a single low-friction overhead cam with two valves per cylinder.

Displacement is 333cc – about the same as a can of beer – and the cylinders use an oversquare 61x57mm bore and stroke that produces peak torque higher in the rev range compared with a square outboard engine – just what you need for running at constant high revs.

The engine is also available in three different drive leg lengths: 381mm (15-inch)/508mm (20-inch)/635mm (25-inch).

For me, what stands out about this outboard engine is the tiller control. Of note, rather than being offset to one side, the tiller is mounted central to the outboard engine, and the tiller arm is ambidextrous.

That means if you’re one of the estimated one in 10 people worldwide who favour their left hand over the right, it’s a relatively simple process to swap sides with its centrally located F-N-R lever, and then reverse the throttle to suit.

You can also give the tiller arm a slight bias to port or starboard.

The control arm also has LED warning lights covering oil pressure, overheating and over-revving, and a large engine stop button in the centre of the throttle control. An engine kill switch clips onto the midsection of the tiller arm’s underside – if you accidentally detach it, you need to raise the tiller arm to reattach it.

There is an adjusting screw on the underside of the tiller arm that allows the user to set the level it comes down to a comfortable height. The arm tilts up to almost vertical, tucking it out of the way when the engine is fully tilted up.

The outboard engine’s cowling, with a single clip, is easy to remove so that you can inspect, service or clean engine components. The oil filter is located low on one side of the engine, making it easy to self-service, but you’ll have to extract the old oil out via the filler.

Prices for the Mercury 15 EFI Fourstroke start from around $4000, with the slightly more powerful 20hp version adding around a $400 premium.

The Mercury 15 EFI Fourstroke have everything you would expect from a modern, portable four-stroke outboard engine, including shallow water drive, start-in-gear protection, rev limiter, multiple trim positions (manually operated with trim-pin slots), kill switch with safety lanyard, and warning systems for potential engine problems.

Mercury outboard engines are sold with a three-year factory warranty for recreational use supplemented with a three-year bonus period if the outboard engine is serviced at an authorised service centre. Industry leader Honda’s warranty is a year longer with five years before the optional two-year extension kicks in

The extra three years, which are transferable to a new owner if you sell the engine with some warranty period still valid, also requires you to follow a strict service schedule and use genuine Mercury parts.

Servicing is every 100 hours or once a year, whichever comes first. A new Mercury engine is also given a three-month/20-hour inspection.

Stating the Mercury 15 EFI Fourstroke is a simple process of pulling the starter cord – a couple of times when cold, and just once if the outboard engine is already warm.

Clever technology that reduces the cylinder compression as you pull the starter cord makes it an easy engine to turn over, with electronic beeps indicating the pull is hard enough to fire the engine into life.

The automatic choke takes care of warm-up, the engine revs dropping slightly to indicate that the Mercury 15 EFI Fourstroke has opened the thermostat and is up to operating temperature.

Operating the Mercury 15 EFI Fourstroke is just like any other portable outboard engine – just twist the throttle and go – but having the gear lever halfway along the tiller arm is a boon compared with some brands that still have the lever affixed to the engine.

With two people onboard and the 98kg AnglaPro Core 374STL punt-nosed skiff hull beneath it, the Mercury 15 EFI Fourstroke is an impressive performer.

Acceleration is brisk, pushing the AnglaPro to an impressive top speed of just below 20 knots under load. Even with the revs nudging the upper limit, the engine remains smooth and vibration-free, minimising fatigue.

At the other end of the scale, the Mercury 15 EFI Fourstroke idles nicely, pushing the boat along at a comfortable walking speed. Acceleration from a standing start is brisk, although it pays to have some weight forward to keep the nose down.

Fuel use was good on test. Even after bombing around Sydenham Inlet looking for photography locations and acting as a chase boat, the Mercury 15 EFI Fourstroke barely made a dint in our tote tank, using maybe a couple of litres.

The engine’s shallow water setting came in handy while beaching in the Sydneham Inlet channel, a wide section of water with shallow spits running down either side.

A grab handle located conveniently on the aft underside of the cowling allows you to easily lift the Mercury 15 EFI Fourstroke and let it settle into its shallow water setting. This trims the engine so it still pumps water, but keeps the prop just below the water’s surface.

At 45 kilos dry, the Mercury 15 EFI Fourstroke is at the upper limit of what one person can carry, so if you’re swapping it out it’s probably best to have a friend around to help.

The only criticism is that the tiller arm is a fixed length, so if you’re in a boat with broad across-thwart seats like the AnglaPro Core 374STL, things are going to be more comfortable with a tiller extension. Make sure you get one that still allows access to the engine stop button, though.

The Mercury 15 EFI Fourstroke is a good little engine for powering a small trailerable boat. Brisk, fuel-efficient, clean and quiet, it easily performs every task asked of it.

Even if you decide you don’t like it, the transferable warranty will make the engine even more appealing to its next owner.