Mercury OptiMax 150 Fuel Consumption

When considering an outboard motor, one of the most critical factors for any boater is fuel consumption. Understanding how much fuel a specific engine will use can significantly impact your budget and the overall enjoyment of your time on the water. In this article, we'll take an in-depth look at the Mercury OptiMax 150hp outboard, a popular choice for many boaters, and explore its fuel efficiency based on real-world testing and its underlying technology.

Understanding the Mercury OptiMax 150

The Mercury OptiMax 150 is a direct fuel-injection two-stroke outboard that sits within a range of Mercury engines from 135 to 175hp. These engines share the same robust 60° V6 powerhead, a design that has a long and distinguished history. This particular powerhead, with its 2.5lt loop-charged configuration, is renowned for its durability and performance. It's capable of producing up to 200hp in its carburetted and EFI (Electronic Fuel Injection) forms. Key to its longevity are its relatively low Wide Open Throttle (WOT) range, typically between 5250 and 5750rpm, combined with a large cylinder bore and a short piston stroke. These characteristics contribute to a reliable and long-lasting engine. In fact, a race-tuned version of this powerhead has been known to achieve speeds of up to 84 knots (155 km/h) in smaller craft.

A significant advantage of the Mercury OptiMax 150, especially when compared to some of its four-stroke competitors, is its design as a true marine engine. It features a diecast alloy cylinder block and head, specifically engineered to withstand the harsh conditions of saltwater cooling. This not only enhances its durability but also ensures that spare parts are readily available. Mercury even provides a convenient rebuild program for the powerhead, offering peace of mind for owners.

Innovative Fuel Injection Technology

At the heart of the OptiMax 150's efficiency lies its advanced fuel injection system. It utilises the Orbital Combustion Process (OCP) developed by Orbital Engine Corporation of WA. This dual-stage direct-injection system operates in both stratified and homogenous modes, setting it apart from other direct-injection technologies. Unlike systems that inject only fuel, the OptiMax injects a mixture of atomised air and fuel. This precise control over the air-fuel mixture is crucial for optimising performance and fuel economy across different operating conditions.

At lower engine speeds, generally below 1500rpm, the system injects an air/fuel mixture with fuel droplets as small as five microns. This mixture is directed in a narrow conical pattern precisely at the spark plug, ensuring a normal air/fuel ratio of 14.7:1. However, within the combustion chamber, the overall ratio can be as lean as 70:1, a testament to the system's efficiency. As the engine speed increases above 1500rpm, the overall air/fuel ratio is adjusted to generate the necessary torque for planing the hull. Furthermore, the fuel/oil ratios are carefully managed, varying from 44:1 at WOT down to a very lean 400:1 when trolling. This sophisticated fuel management makes the 150hp OptiMax remarkably economical for its power output. The standard in-boat oil tank capacity is 11.4 litres.

On-Water Performance and Fuel Economy

During testing, the Mercury OptiMax 150, weighing 201kg in its extralongshaft (25in) configuration, proved to be considerably lighter than many direct four-stroke competitors. In a test on an Archer 58C plate-alloy cuddy cabin, pushing a total weight of 1350kg and fitted with an 18-inch pitch Quicksilver Mirage stainless steel propeller, the engine demonstrated impressive performance. While the test unit felt slightly overpropped and might have benefited from a 17-inch prop, it ran flawlessly. The vibration levels were low across the entire rpm range, and harmonic resonance transmitted through the hull was minimal.

The holeshot acceleration was a standout feature, on par with other 150hp DFI two-stroke outboards. The characteristic Mercury V6 “howl” only became noticeable at higher power settings. However, it's worth noting that the OptiMax 150 was still generally noisier than its four-stroke counterparts. In sharp, full-lock figure-of-eight turns at 4000rpm, there was no prop ventilation, an admirable feat for a plate hull with a long external keel.

Starting the engine, whether hot or cold, was instantaneous. No oil smoke was observed at any time, and there was no noticeable oil smell, even when backing upwind. The only minor critique was the “notchy” shifting action of the Mercury control box, which could be improved. With the antiventilation plate kept at least three-quarters submerged, the engine provided good power astern without any signs of cooling water starvation.

Perhaps the most compelling aspect for many boaters is the fuel consumption during trolling. The Mercury OptiMax 150's fuel usage when trolling was comparable to that of a 60hp four-stroke outboard and even a carburetted 25hp two-stroke. This is an exceptional achievement for an engine of this power. In a remarkable demonstration of its efficiency, after one hour of performance testing, the 150 OptiMax consumed only 9.5 litres of fuel. This is an outstanding figure for any 150hp outboard motor.

Accessibility and Maintenance

Access to the powerhead for maintenance is designed to be straightforward. Key components such as the belt-driven air compressor and the 60amp/h voltage-regulated alternator are easily reachable. The air and fuel injectors are also neatly grouped, simplifying servicing. Mercury Marine recommends servicing the OptiMax 150 every 100 hours or annually, with the initial service due at 20 hours. Adhering to these service intervals at an authorised service centre ensures the five-year recreational usage warranty remains valid.

Performance Data and Comparisons

To provide a clearer picture of the Mercury OptiMax 150's fuel consumption across various speeds and engine loads, here is a breakdown of its performance data:

It's important to compare this with its direct competitor, the Evinrude E-TEC 150XL. While the Evinrude E-TEC 150XL was priced at $19,674 in April 2011, the Mercury OptiMax 150 had a recommended retail price of $19,000. The Evinrude also featured a 60° V6 2.6lt engine, weighed 194kg, and came with a 3-year warranty, earning 3 OEDA stars. The Mercury, with its 2.5lt powerhead, was slightly heavier at 201kg but offered a 5-year warranty. These figures highlight that while pricing and some specifications may vary, the fuel efficiency of the OptiMax 150 is a significant selling point.

Frequently Asked Questions

Q1: How much fuel does a Mercury OptiMax 150 use when trolling?

When trolling, the Mercury OptiMax 150 is remarkably efficient, using approximately 0.8 litres per hour at idle speeds (around 550rpm) and around 10.2 litres per hour for offshore trolling (around 2200rpm). This is comparable to much smaller engines.

Q2: What is the fuel consumption at Wide Open Throttle (WOT)?

At Wide Open Throttle (around 5000rpm), the Mercury OptiMax 150 uses approximately 59.0 litres per hour. This is typical for an engine of this horsepower operating at maximum output.

Q3: Is the Mercury OptiMax 150 a fuel-efficient engine?

Yes, the Mercury OptiMax 150 is considered a very fuel-efficient engine for its class, especially at cruising speeds and when trolling. Its advanced direct-injection technology allows for precise fuel delivery, resulting in impressive economy.

Q4: What is the fuel injection system used in the Mercury OptiMax 150?

The Mercury OptiMax 150 uses the Orbital Combustion Process (OCP) dual-stage direct-injection system, which injects a mixture of atomised air and fuel for optimal combustion and efficiency.

Q5: How does the Mercury OptiMax 150's fuel consumption compare to four-stroke outboards?

While the OptiMax 150 is a two-stroke, its direct-injection technology allows it to compete very favourably with many four-stroke outboards in terms of fuel efficiency, particularly at lower and mid-range speeds. Its trolling fuel consumption is notably on par with much smaller four-stroke engines.

Conclusion

The Mercury OptiMax 150hp outboard motor stands out as a powerful and remarkably fuel-efficient option. Its innovative direct-injection system, robust construction, and excellent on-water performance make it a compelling choice for a wide range of boating applications. The data clearly shows that for its horsepower, the OptiMax 150 offers exceptional fuel economy, especially during trolling and efficient cruising. While it might be slightly noisier than some four-stroke alternatives, its overall package, including reliability, performance, and crucially, its low fuel consumption, makes it a strong contender in the 150hp outboard market.