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MerCruiser Engines FAQ

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What are the main differences between the Alpha and Bravo® Drives?

The Alpha and Bravo series drives are designed to meet the specific needs of different boat applications. The Alpha is ideally suited for small to mid-size runabouts and cruisers and offers an outstanding combination of features, durability and value. Near net forged gears, a floppy vane water pump impeller and dog clutch are just a few of the components that make this a popular drive. The Bravo series features extra heavy-duty shafts and bearings to withstand the demands of larger boats and performance-oriented applications. Bravo drives incorporate steel cone clutches for smooth, reliable shifting and precision-forged gears (on the Bravo I and III) for added strength and durability. Both the Alpha and Bravo series offer Power Trim XD, anti-feedback power steering, drive lube monitor and an audio alarm system (optional on 3.0L).

What are the differences between the Bravo I, Bravo II and Bravo III Drives?

Bravo I's smartly styled hydrodynamic gearcase is designed to excel under the high stress requirements of today's performance boats. Its sleek design is made possible by the use of MerCruiser's exclusive precision forged gears that afford exceptional strength for their size. Constructed with larger shafts, bearings, upper gears and MerCruiser's own heavy-duty universal joint, this drive easily handles the power and torque of big block engines.

Bravo II is a perfect match for demanding applications where added thrust is required to get a larger boat moving. Bravo II drives accept a larger diameter propeller (up to a 20") which improves planing characteristics and provides significantly higher reverse thrust for greater stopping power and better maneuverability.

Bravo III represents the ultimate power for everything from runabouts to large cruisers. This drive features twin counter-rotating propellers for exceptional boat trimming and handling ability.

What are the differences between a carbureted engine and an electronic fuel injection (EFI) system?

MerCruiser offers both carbureted and electronic fuel injected (EFI) systems. The carbureted system relies on atmospheric pressure and air flow through the engine to draw fuel through the carburetor. This approach provides a cost effective method of metering fuel to the engine, but does not provide the precision and operating refinement of an EFI system. With the EFI system, pressure is delivered to injectors at 30 psi — 43 psi. An electronic brain that monitors a multitude of engine conditions and precisely controls the flow of fuel to the engine electronically controls these injectors. With fewer components to wear out and improved compatibility with today's fuels, the boat owner ultimately can achieve greater reliability and reduced operating costs.

What is Thunderbolt V?

The Thunderbolt V ignition system is standard on all carbureted V-6 and V-8 gasoline models. Programmed on the MerCruiser production line to the specific engine model requirements, Thunderbolt V offers valuable operating benefits, including faster, easier starting; smooth low speed trolling operation; quicker, more positive throttle response; improved fuel economy, unaffected by hot or cold weather; minimized ignition tune-ups and parts replacement; and protection from over-speed damage. Knock control (standard on all EFI sterndrives, ski and inboard models) also protects the engine from poor quality fuel (not offered on any carbureted models, except the 5.7L, which is standard).

What are the benefits of the MerCruiser SmartCraft™ MPI system?

All SmartCraft models feature a new, highly refined multiport fuel injection system run by the Mercury-exclusive 555 engine control module. The 555 control module monitors up to 64 internal functions and gathers data from inside and outside the boat. By monitoring the inputs, the system automatically optimizes fuel mixture and ignition timing, resulting in improved, precise performance that translates into more powerful and efficient engines.

What kinds of engine protection systems does MerCruiser use?

All carbureted models (optional on the 3.0L) feature the Audio Warning System, which uses an under-helm mounted warning horn that alerts the operator to potentially engine-damaging conditions, such as low oil pressure, high engine temperature, low drive lube level (sterndrives), or excessive transmission temperature (inboards). The Mercury-exclusive Engine Guardian™ system takes marine engine protection to new levels by not only detecting and alerting the operator about these conditions, but also by processing the data and automatically reducing power to a safe operating level. In addition, Engine Guardian monitors cooling water pressure, providing an early warning to the 555 controller of the potential for high engine temperatures. Any incident that activates the system is logged by the controller and is accessible by a Mercury MerCruiser technician for diagnostic troubleshooting.

Sterndrive Corrosion Resistance

In an effort to make their sterndrive packages stronger and more reliable, MerCruiser exposes the complete propulsion system to rigorous saltwater testing, condensing a lifetime of boating into one year or less. As a result of this extensive testing they have developed some of the most corrosion-resistant sterndrives in the industry. Here are some of the most important features:

XK-360 Alloy. This unique low-copper aluminum alloy used to cast many of the sterndrive components is proven through immersion testing to be superior to industry standard alloys.

Multi-step Painting Process. To assure proper paint adhesion, each part is put through a 14-step cleaning and coating process. This process includes a zinc chromate primer, epoxy and acrylic paints applied via computer controlled ElectroDeposition Painting (EDP) process for a more uniform coverage. The paint formula also contains plasticizers to help resist chipping. Components are then baked to seal the painted metal in a non-chipping protective coating.

Sacrificial Anodes. Sacrificial indium/aluminum alloy anodes are strategically placed on the sterndrive unit to sacrifice themselves to corrosion (be eaten away) while the important components are unharmed.

MerCathode. Neutralizes the corrosive current with a blocking current of its own, which reduces the need for periodic inspection of anodes (a nice feature on larger boats that are left in the water).

4" Exhaust Elbows. A larger passageway in the exhaust elbow prevents saltwater clogging. To improve life in saltwater, MerCruiser manufactures the elbows from cast iron using lost foam casting process to provide better control over the wall thickness, preventing thin spots that can corrode through prematurely. Many models feature a ceramic coating baked on between the epoxy paint and cast iron surface, coated both inside and out for an added layer of corrosion protection.

What is the 3-year limited corrosion failure warranty and what does it cover?

All standard production MerCruiser gas sterndrive and inboard packages are protected by Mercury Marine's exclusive 3-year limited warranty against corrosion failure. For complete information, please consult the MerCruiser Operation & Maintenance Manual.

Did You Know? Facts About Mercruiser SternDrives

  • Power steering is standard on all MerCruiser sterndrives 4.3L and larger, optional on the 3.0L.
  • 3- and 6-inch risers which prevent saltwater clogging are a factory-installed option available on all MerCruiser sterndrives and inboards, except the 3.0L.
  • Remote oil filters are standard on all gas fuel-injected sterndrives, Bluewater Inboards and diesel engines, and are available as a kit on all carbureted sterndrive models.
  • MerCathode is standard with all Bravo drives (kit available through Mercury Precision Parts for Alpha drives).
  • The Audio Warning System (mounted under the helm) alerts the boater to low oil pressure, high engine temperature, excessive transmission temperature (inboards), AND low drive lubricant (sterndrives). Standard on all gas and diesel models, available as a kit on the gas 3.0L sterndrive.
  • All MerCruiser V-6 and V-8 models feature an innovative dry-joint exhaust system design, which eliminates water leaks into exhaust passages. These exhaust systems receive special coatings, including EDP and ceramic, to resist corrosion under tough saltwater usage.
  • Engine Guardian™, standard on all SmartCraft™ MPI models, detects, alerts the operator and proactively reduces engine power level to protect the engine and drive from the potentially damaging effects of low oil pressure, low water pressure, high engine temperature, high exhaust manifold temperature (496 MAG and 8.1S models) and low drive lube (sterndrives) or high transmission temperatures (inboards).

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