Mercury Optimax 150

Since its local release in 1998, the Optimax 150 has proven very reliable. Sure, there have been minor problems such as fuel injector failures, but it has never suffered the rapid combustion carboning-up problems that afflicted Evinrude's FICHT 150 of the same era. And unlike FICHT models, it doesn't require a special oil to function reliably.

The Optimax 150 utilises the long-running 2.5lt powerhead that is still used in carburetted models out to 200hp.

It has all the Optimax features such as the dual-fuel Orbital Combustion Process (OCP) system that mixes air with fuel before it's injected into the combustion chambers, resulting in fuel atomisation down to five microns - up to five times finer than Yamaha's HPDI system. The OCP also operates on a mix of 'stratified' and 'homogenous' combustion, with the air/fuel ratio as lean as 40:1 when trolling or about four times leaner than a carburetted 150. The Motorola microprocessor automatically alters the air/fuel ratios according to engine load and barometric pressure. Also, when the engine is brand new or has been reconditioned, the management system can be programmed to automatically double the fuel/oil ratios for the first five hours.

And like all Optimax models it's SmartCraft-compatible, allowing it to operate digital fuel-flow meters, range-to-empty and other goodies associated with this brilliant system. It can also be fitted with TrollControl, which reduces trolling revs to a mere 400 - ideal for serious freshwater or livebait trollers.

I recently tested a 150 on a 6m Seafarer Victory. Spinning a 17in Quicksilver Vengeance stainless steel prop, it handled the five-adult load much better than expected.

The demo motor started instantly, hot or cold, and never emitted oil smoke, nor was there any oil smell in following winds. Provided the antiventilation plate was kept at least three-quarters immersed, power astern was good and no cooling water starvation occurred. Vibration levels across the entire rev range were incredibly low, and only at low speeds was the air compressor noise apparent (but not as noticeable as an Optimax 135 I tested a while ago).

Pushing a total of 1800kg, according to my Lowrance GPS the 150 trolled at 4.7kmh on 650rpm, consuming an unbelievably low 1.1lt/hr, which is less than a four-stroke Mercury F90 uses when trolling. Increasing the revs to 1000 returned a wake-free 7.0kmh consuming 2.4lt/hr. At 2000rpm the average was 13.0kmh, ideal for offshore lure trolling. At these revs the 150 still used only 8.3lt/hr.

Despite the hull load and subsequent overpropping, the 150 achieved a clean plane at 29.7kmh on 3200rpm, consuming 18.8lt/hr and cruised quietly at 48.1kmh on 4000 using 25.7lt/hr. Through tight figures-of-eight at these revs, there was no prop ventilation and the microprocessor maintained engine speed within a 100rpm range through the turns.

Over a 15cm windblown chop the Wide Open Throttle average was 65.8kmh on 5050rpm consuming 57.9lt/hr, still very reasonable for a 150hp outboard. Noise levels were sufficiently low for us to converse normally at the helm.

Despite its apparent undercowl complexity, servicing the 150 is straightforward. Mercury Marine's recommended intervals are every 100 operating hours or once a year (also for waterpump impeller replacement) after the first 20 and 50 hours. Ken Bullen Marine, which supplied the demo motor, suggests checking and/or changing the 1:1 air compressor belt drive every 100 hours. Unlike Yamaha's HPDI system, which has a limp-home mode should the high pressure injection pump fail, the compressor is crucial to the operation of the OCP system.

Mercury Marine fits pure aluminium anodes to its outboards. These erode very quickly in saltwater, so it's important to replace them after about 100 hours of immersion or surface rust may appear on lower unit bolts and the stainless steel prop. But providing this is done, the 150 has a proven reputation for saltwater survival.

For recreational applications the warranty provides two years of general coverage, three against corrosion perforation and four for selected ignition components.