Mercury Four Stroke 150 outboard review

When Mercury released its FourStroke 150 outboard two years ago it was love at first sight. This engine was so good it actually made me rethink my love of direct fuel injection two-strokes. And while the FourStroke 150 outbord motor doesn’t deliver the incredible trolling fuel efficiency of the Mercury OptiMax 150 it scores with better midrange efficiency, which is the forte of all four-stroke engines.

According to my local Mercury dealership, which moves a lot of larger outboards, the FourStroke 150 has proved more popular with anglers than the OptiMax because of its midrange efficiency and because it’s fairly light for a four-stroke Mercury 150. Absolutely no servicing issues have arisen.

The OEDA 3-star Mercury 150 has the biggest piston displacement of all the 150hp four-stroke outbords in our market, even though at 147.5hp at 5500rpm its power output is similar. The Wide Open Throttle range of 5000 to 6000rpm allows for some propping flexibility.

The Mercury's 3lt four-cylinder engine has chain driven SOHC actuation for the eight valves and the twin counter-rotating balance shafts are gear driven at the bottom of the crankcase, not at the top or bottom of the engine. Roller finger followers, where the camshaft lobes are in constant mesh with the rocker arms, eliminate the need for valve clearance adjustments.

A simple single-throttle body feeds the multipoint fuel injection. The oil dipstick and canister filter are easily reached, and the drain plug with spout in the leg reduces oil dribbles down this when the oil is changed. Quicksilver FCW SAE 10W30 oil is recommended for temperate climates.

The belt driven 60amp alternator produces 30.6amp at 1500rpm, with a maximum of 46.3amp available for battery charging. The dry extra-longshaft engine weight is 213kg and the gear ratio a usefully low 1.92:1.

Servicing is straightforward with 100-hour or annual intervals after the first 20 hours. The warranty for us recreational anglers is five years.

ENGINE PERFORMANCE

Sadly the Mercury FourStroke 150 outbord motor has less flab reduction qualities than its OptiMax counterpart, with none of the slight shaking that occurs when the stratified combustion switches to homogeneous. There’s nothing but smooth, effortless power delivery across the entire rpm range, with better than expected bottom-end torque for clean holeshot. The demo engine started instantly hot or cold with no oil smoke appearing and though the absence of drive-by-wire electronic throttle/gearshift, the controls did give more of a clunk when forward or reverse were engaged, the shift shock less than an OptiMax.

Mounted on a Kiwi-built FiGlass 6.4 Warrior cuddy cabin and swinging a 17in Quicksilver Enertia prop, the review Mercury FourStroke 150 planed our 1850kg total weight, including four adults, from trolling to planing speed in just four seconds. The bottom-end torque appeared comparable to the Mercury OptiMax, with a clean plane at well under 3000rpm in calm water and an ability to stay planing at 3000rpm in rolling ocean swells, and keep on the backs of waves without constantly playing the throttle. No wonder offshore anglers love this engine!

Through tight turns at 4000rpm in calmer water, absolutely no prop ventilation occurred and the sheer grunt of the 150 returned higher upper-throttle opening speeds than I would have expected with remarkably low mechanical noise and no balance shaft whine at WOT. There was no OptiMax V6 howl, but no outboard engine is perfect!

THE TRADE-A-BOAT VERDICT

It was the right choice of Mercury Marine to develop the marine-specific Mercury FourStroke 150 outbord motor  in-house instead of rebadging an automotive-derivative engine from another manufacturer. With its way low XK360 alloy copper content of 0.2 per cent the Mercury 150 outboard motor is guaranteed a long life in saltwater. It’s servicing simplicity is refreshing after the complexity of its direct competition and although its quiet, smooth operation won’t enhance your tinnitus or reduce flab, the 150 still makes a great repower engine for older ’glass hulls to six metres.

As of January 2014 the extra-longshaft model had a price of around $20K, with a spare prop coming in at $1100. Thanks Mercury Marine, Dandenong, VIC, phone +61 03 9791 5922, for supplying such a well-prepared demo engine. 

MERCURY 150 FOURSTROKE PERFORMANCE

COMPETING OUTBOARD ENGINES