Mercury OptiMax 115 Outboard Engine Review

Only three direct fuel injection (DFI) two-stroke outboards in the 115hp range are available: the Evinrude E-TEC 115, Tohatsu TLDI 115, and Mercury OptiMax.

The E-TEC and TLDI engines have four cylinders and are relatively smooth across the entire rev range.

However, that is not true with the Mercury OptiMax 115 outboard motor. Its big-displacement three-cylinder powerhead sends vibration waves through the hull structure at less than 1000rpm, guaranteeing gentle flab reduction whenever you grip the hull or steering wheel. And it’s a little rougher than the competition over 1000rpm.

Power and Efficiency

The most powerful of a trio of DFI two-stroke outboards from 75hp, the three-star OEDA-rated Mercury 115 develops 113.3hp at 5375rpm from its 1526cc loopcharged powerhead and has a Wide Open Throttle range of 5000-5750rpm.

Developed by WA’s Orbital Engine Corporation, the Mercury OptiMax DFI is a two-stage system that mixes air with fuel before injecting the atomised mix directly into the combustion chambers. I don’t want to put anyone to sleep, so I won’t go into operational details. However, it suffices to say that this DFI system has incredibly low trolling fuel and oil consumption with traditional two-stroke outboard performance.

A belt-driven, voltage-regulated 60A alternator provides plenty of power for electronic toys. Since the only other belt is for the air compressor, the 115 is relatively trouble-free compared to 115hp four-strokes. The dry weight is 170kg for the long shaft version (175kg for extra-long), and the gear ratio is 2.07:1, which is a little taller than its OptiMax 75 and 90 counterparts.

Powerhead access is good even though a 4.7L oil tank is fitted. Mercury recommends servicing every 100 hours or annually after the first 20 hours, and the engine has a five-year recreational use warranty.

Impressions on the Water

A hull that could handle 230kg was a good match for the demo Mercury 115 engine and the Stacer 565 Coral Master Sports Runabout, which was planned at incredibly low speeds. It easily lifted out of the hole, and the Mercury 115 planed cleanly from trolling revs in 2.5 seconds, despite swinging an 18-inch prop and pushing a total of around one tonne, including two adults.

The Merc 115 started instantly hot or cold with no oil smoke, and, provided the anti-ventilation plate was kept at least three-quarters immersed. It was great for backing off estuarine sandbars. However, the Mercury remote-control box was a tad notchy in its operation.

At less than 1000rpm, we appreciated that Mercury had opted for such a large-displacement three-cylinder engine and that we didn’t have to endure the same vibration level through the hull at engine speeds of over 1000rpm. Few four-stroke 115s could maintain a clean plane at only 2700rpm, and the 115 was incredibly fuel efficient at the most economical cruise speed of 3000rpm. There was no prop ventilation through tight turns at 4000rpm, and the 115 let us know it was working hard for our enjoyment at WOT.

The Verdict

The Mercury OptiMax 115 outboard motor compromises between the lower but wider profile of the V4 E-TEC 115 and the tall stature of the in-line TLDI 115. It’s cheap to run for a 115, and with Mercury’s proven saltwater corrosion protection and outstanding warranty coverage, it’s a logical re-power choice for older hulls. Parts are easily available across Australia because the 115 uses the same pistons and other components as the V6 OptiMax 200-250 range.

Throw in the fact that the Orbital Combustion Process has been the most trouble-free system of the three DFI options on the market, and the OptiMax 115 represents very good value. As of May 2013, the extra-long-shaft 115, including prop and installation, was quoted at $13,140 (Melbourne dealer). A spare Vengeance prop retails for around $1000.

Thanks to Lifestyle Marine, Toronto (NSW) — call (02) 4959 1444 or visit www.lifestylemarine.com.au — for the use of the demo engine.

Mercury Optimax 115 Performance

Competitor Comparison

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This article was written by and photos provided by Kevin Smith and previously appeared at TradeaBoat.com.au, now powered by Only Boats.

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