Mercury 150 EFI

When Mercury Marine's EFI range of outboards were released in Australia in the late '80s, they provided boaters with the convenience of turnkey starting, just like an EFI car.

Basically, Mercury's EFI system is the same as that in an EFI car engine and injects fuel at the reed valves via an Electronic Control Unit (ECU) that continuously monitors air and engine temperature, throttle position, engine revs and barometric pressure, altering the air/fuel ratios accordingly. This enables Mercury's EFI engines to run as well on high altitude alpine lakes as they do at sea level, eliminating the need for the 'hit or miss' starting of choke-equipped motors.

But unlike Mercury's Optimax models, some unburnt fuel is released before the pistons close off the exhaust ports and the fuel/oil ratios are the same as carbie models. The combination of these factors prevents the EFI models from complying with the US EPA 2006 exhaust emission regulations, let alone California Air Resources Board (CARB) requirements.

However, there are still no plans to introduce EPA or CARB-style regulations onto the Australian market, so providing Mercury Marine continues to manufacture these motors they will be available locally past 2006.

The 150 EFI is the smallest of Mercury's EFI models and is based on its reliable 2.5lt powerhead. EFI models utilising this powerhead range from 150 to 200hp.

Standard features include Modular CD ignition, a 40-amp under-flywheel alternator with dual battery charging capability and an electronic engine warning system equipped with a high-pitched alarm.

The demo motor was supplied with full instrumentation including a water temperature gauge (more on this later).

Mounted on an 6.55m Allison Vision 21 spinning a 17in pitch Quicksilver Laser 11 stainless steel prop and pushing a total of 1450kg including two adults, safety gear and two thirds-full fuel tank, the demo motor was well matched to this hull though slightly under-propped.

However, add a full fuel load of 260lt, four adults and fishing tackle, which would bring the total to about 1800kg, the 17in prop would be ideal.

The demo motor started instantly hot or cold with oil smoke appearing only for the first five minutes, and had much lower vibration levels than a 175 EFI I tested a few years ago.

The motor warmed quickly from cold, and providing the anti-ventilation plate was kept at least three quarters immersed, power astern was good.

Trolling at 800rpm the 150 EFI averaged 5.8kmh and at 1000rpm reached 8.2kmh. At the normal offshore trolling revs of 2000, the average speed was 12.4kmh.

Despite the Allison having a half pod that wasn't flush with the hull bottom, a clean plane was achieved at just 24.6kmh at 3000rpm. At 4000rpm the Merc averaged a quiet 50.2kmh consuming 35lt/hr. Through tight figure-eight turns at 4000rpm there was some prop ventilation, but under normal circumstances this shouldn't occur.

At Wide Open Throttle the Merc averaged 74.1kmh on 5900rpm using 59lt/hr, and although the normal Merc V-six 'howl' was present it wasn't loud enough to prevent us conversing normally at the helm.

Unfortunately the demo engine overheated whenever we dropped off the plane. Above 3000rpm there was sufficient water pressure through the cooling water passages to overcome this problem, but at low speeds (when V-six Mercs always run hotter) the gauge needle was on the 'high' mark in a couple of minutes, accompanied by an ear-splitting alarm.

This is the first time I've encountered an overheating problem with a V-six Merc, but it did prove the value of a temperature gauge!

Powerhead access is very good and recommended servicing intervals are every 100 hours or once a year (which also applies to waterpump impeller replacement) after the first 20 hours.

The EFI 150 has a proven reputation for survival in saltwater and in my opinion is worth every cent over carburetted motors of the same size.

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