Mercury
250 OptiMax Pro XS
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Mercury 250 OptiMax Pro XS Mercury 250 OptiMax Pro XS main video
Mercury Marine's 250 XS has been highly successful in boat racing, and the 250 OptiMax Pro XS builds on that success. It is available in 20'' and 25” (50.8 cm - 63.5 cm) shaft lengths it is outfitted exclusively with the robust Torque Master gearcase. When designing the 250 OptiMax Pro XS Mercury set its sights on bass boats, deep-V walleye and saltwater bay boats. However this engine has quickly become a popular choice on the tournament circuit thanks to its power-to-weight ratio, which is the best in class.

Mercury 250 OptiMax Pro XS (Outboard) Specifications
Number of Cylinders 6 Cylinders
Configuration V-drive
Weight (lbs/kg) 505.00 lbs / 229.06 kg
Fuel Delivery Fuel Injected
Displacement (cu/cc) 183.00 cu / 2,998.83 cc
Shaft Length Options L- 20 '' (508 mm) XL- 25'' (635 mm)
CARB Rating 3-Star
Recommended Fuel 87 octane
Alternator Output 60 A
Engine Monitoring System Standard

Mercury 250 OptiMax Pro XS Captain's Report

Mercury 250 OptiMax Pro XS

The Mercury 250 OptiMax Pro XS was tested in a tournament bass boat where we reached a top speed of over 75 mph.

Improved Design

Several factors have gone into the 250 OptiMax Pro XS that make it such a standout, but most will not be seen or felt by the end-user. These include racing design components such as carbon fiber reeds, solid billet aluminum mounts, and special dome shaped coated pistons. Mercury has also made significant improvements in noise and vibration.

Efficient Design

The 250 Pro XS benefits from Mercury's efficient OptiMax two stage fuel injection system. This system uses a charge of fuel and air to atomize fuel droplets directly into the combustion chamber, providing better fuel economy and lower emissions.

Corrosion Protection

The 250 OptiMax Pro XS features a high torque starter with a gear reduction added on. Mercury has added MercFusion paint to the starter to reduce corrosion, particularly in a saltwater environment. Additionally, this engine uses aluminum alloys to reduce copper content in the metals. Mercury manufacturers it’s own aluminum-silicon alloy and says that its alloy has the lowest copper content. Lower copper content means less corrosion.

Mercury 250 OptiMax Pro XS

The silver gearcase denotes that this is the pro series Torque Master gearcase for heavier loads and higher speeds.

Painting Process. It’s a three-step process over the low cooper alloy metals. First Irridite metal prep and sealing provides a highly resistant barrier and a good foundation for the paint process. Then it’s on to EDP, Electro-Deposition Priming. This process uses electrically charged paint and oppositely charges components for a uniform coverage that seals out the corrosive environment.

Finally it’s on to the powder coated top coat. Again, oppositely charged paint and components are used to adhere to the paint powder, and plasticizers are added not only for flexibility but better long term adhesion. After it’s sprayed on it’s baked creating a finish that is harder, thicker, and tougher than conventional paint.

Mercury 250 OptiMax Pro XS

Low speed intake vents not only serve to keep the engine cool during idling, but also compensate for higher altitudes.

Features Inspection

The Mercury 250 OptiMax Pro XS is a V-6, 60-degree, 3L displacement engine. It has a dry weight of 505 lbs. (229 kg), is water cooled, naturally aspirated, and has 2-stage direct injection designed to run on 87 Octane fuel with up to 10% ethanol.

Mercury 250 OptiMax Pro XS

This vapor separator pressurizes the fuel creating a more fuel efficient burn in the combustion chamber.

Oil Delivery

The multi-point oil injection pump is a big deal as it not only lubricates the components, but cools and cleans them as well. It’s computer controlled to deliver the right amount of oil to the components whether during break-in, hard running, or idle speed. There’s a remote oil tank in the boat with a second oil tank on the engine that includes sensors for low and no oil. Rather than pump the oil from the remote tank, it is instead forced into the engine mounted tank from crankcase pressure. From there it goes to the multi-point oil pump with its several discharge ports. These feed oil to all six cylinders with the ratio controlled by the PCM… the onboard computer.

Mercury 250 OptiMax Pro XS

The multi-point oil pump not only delivers oil to the components, it also cleans them.

The Silver Bullet

This engine comes standard with the silver gearcase that signifies that this is the Torque Master gear case, which is standard on the Pro XS and is designed for heavier loads and boats hitting speeds up to 85 mph. In the front of the hydrodynamic gearcase are low speed water intakes that compliment the side mounted intakes and these will also ensure optimum cooling at higher altitudes.

Mercury 250 OptiMax Pro XS

There is both a large primary and a smaller, secondary anti-cavitation plate. The smaller one directs water flow over the side intakes and then towards the propeller giving better performance and more top speed.

May the Force Be with You

Because these engines are equipped with a right hand turning propeller, the heavy torque pushes the gearcase to the right. That can get hard on the mechanics of the steering as well as the operator, so Mercury added a cambered skeg with a flair to the right side that counters the propeller torque and takes the strain off. It also gives a straighter hole shot.

Mercury 250 OptiMax Pro XS

The vents in the propeller aerate the water around the propeller allowing it to spool up to speed quicker and give a faster hole shot.

Prop Vents

The propeller utilizes Mercury’s PVS, or Performance Vent System which works particularly well with heavily loaded tournament rigged bass boats to get on plane quicker. With conventional props, water restricts the rotation of the propeller as it accelerates. By venting the exhaust out the front, the prop is aerated, and allowed to accelerate quicker. Different sized plugs allow users to fine tune the performance.

Mercury 250 OptiMax Pro XS

Here we can see 1) the high torque starter and notice it’s painted to reduce corrosion, 2) the familiar terminator plug for plugging in diagnostics, and 3) the connectors for digital and analog gauges, whichever the customer prefers.

Performance

So how does it all come together? We tested the Mercury 250 OptiMax Pro XS on a Ranger Z521 tournament bass boat with an empty weight of 1900 lbs. (861.8k g). With full fuel, two people and the 505 lb. (229 kg) engine, we had a test weight of 2,969 lbs. (1,347 kg).

With the 250 Pro XS turning a 14 x 25 three blade stainless steel Fury propeller with 12 mm vent plugs we reached a top speed at 5800 rpm of 75.1 mph. At that speed the 250 Pro XS was burning 22.8 gallons per hour giving the Z521 a range of 71 miles.

Mercury 250 OptiMax Pro XS

Our test results of the Mercury OptiMax 250 Pro XS TM with a 14 x 25 Fury prop on a Ranger Z521 tournament bass boat with full fuel two people and the 505 lb. (229 kg) engine we had a test weight of 2,969 lbs. (1,347 kg).

Best Cruise came in at 3000 rpm and 30.5 mph. That speed reduced the fuel burn to 6.2 gph and gave us a range of 106 miles and an endurance of three hours and 30 minutes while still maintaining a 10% reserve.

We had a time to plane of 6 seconds, reached 20 mph in 8.5 seconds, 30 in 10.3 seconds, 40 in 12.6 seconds, and continued accelerating through 50 mph in 15.6 seconds.

Mercury 250 OptiMax Pro XS

Few things are as thrilling as blasting across the surface of the water at 75 mph.

Handling

The Mercury 250 OptiMax Pro XS had remarkable responsiveness. It brought us up on plane in short order. Pulling the throttle back showed that it settles into any rpm steadily with no hunting. With a 120 degree turning radius, handling was effortless with no feedback thanks to the hydraulic steering. The mid-range responsiveness can be seen here, where we cruised at 50 mph, the maximum speed of the camera boat, and then quickly accelerated to the 75 mph, the maximum speed of the test boat. When taking power off, I noticed no freewheeling of the propeller which seemed to bring us off plane in a timely manner. Low speed maneuvering was also excellent.

Observations

Mercury’s 250 OptiMax Pro XS is one seriously robust engine and with the Torque Master gear case it should be up to the challenges of hard use over a long period of time. We drove it like we stole it during our tests and it never wavered from top performance. We're told by Mercury that this engine is the number one choice on the tournament circuit. We think for offshore fisherman, it’s equally appealing.


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