Best Motor Oil for Your Boat’s Engine

Boat motors are expensive, so using the best marine motor oil is critical to protecting it in the harsh environments they operate in.

Have you ever really thought about the differences in how your boat’s engine is used compared to your car’s engine? Do you know why it’s important to understand these differences, so you can choose the best oil?  This article will talk to you about some of these differences and introduce you to the best synthetic motor oils on the marine market, manufactured by AMSOIL. 

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What’s different

The wet and sometimes salty environment it operates in, the amount of use it gets, high RPM’s and constant load are just a few.  Compared to your car’s engine, these are some of the harshest environments that can be encountered. Add to this list, that maintenance is usually not at the top of the priority list.  So, when you choose an oil for your boats engine, using one that is designed to give you the best protections in those conditions is a must. 

Whats high stress

Consider that a marine engine powering a boat at 30 mph runs about 5,000 rpm. In contrast, an automotive engine powering a car at 60 mph runs about 2,000 rpm. This higher stress causes traditional oils to break down and lose viscosity. This leads to deposit formation, reduced power and eventually engine failure.

How does rust come into play

Due to constant exposure to humid, wet environments, marine engines are prone to rust and corrosion. Rust on engine parts acts like sandpaper, scouring bearings, the cylinder wall, piston rings and other components, while aluminum pistons and other parts can corrode. Rust and corrosion reduce engine power and eventually cause catastrophic failure. Rust protection is not natural to motor oil; it comes only by design from the additives added to it.

Storage

When a marine engine sits in storage for the winter season, all the acids and water introduce to the oils can lead to rust formation on the internal parts. When the engine starts up again, damage will caused to the cylinders and bearings. Extending your rust protection to the off season comes into play.

Results of the Marine oil E-TEC engine study.
Test results from the E-TEC field study.

Who makes oils

Reading a recent article about marine engine oils, I had to laugh when the author started talking about engine makers formulating oils.  Engine makers don’t formulate motor oils, the oil manufacture’s formulate oils.  Just as designing engines to meet the newest standards is a continuous process with lots engineering and testing, Formulating oil to meet the latest standards in a variety of operating environments takes the same amount of engineering and testing.  On top of all that goes into developing oils, testing oils is expensive and ongoing. Most people don’t understand that every time and oil formulation is adjusted, it must go through the tests all over agin to be re-certified.

Who makes the standards

The National Marine Manufacturers Association (NMMA) developed the standards and testing procedures for certification for Marine Engine Oils.  These certifications are FC-W, FC-W (CAT)  and the TC-W3.  The goal of these oil certifications is to reduce emissions, increase fuel mileage and design oils specifically for the marine environment. 

Here is a link to the NMMA if you want to read more about them.

FC-W and FC-W (CAT)

These oils are designed for the 4 stroke marine engines being produced.  The FC-W (CAT) category is for the newest marine engine technology that has exhaust after treatments to further reduce emissions.  These FC-W (CAT) oils are catalyst compatible. 

Four Stroke Marine Oil Certification Testing

Who develops the tests and what are they testing for?   Directly from the NMMA site: “Working with the NMMA, industry leaders in lubrication technology developed testing criteria for this marine four-stroke oil. These criteria include bench tests for viscosity, corrosion, filter plugging, foaming and aeration. In addition, the oil must successfully pass a 100-hour general performance engine test.”  

The FC-W (CAT) certification takes into account the need to protect the catalyst in marine engines with exhaust after-treatments in addition to all the normal performance criteria of the FC-W oils.

TC-W3 

Two stoke oils lubricates engine parts as it passes through the engine and is burned off with the fuel.  Two stoke oils can be either mixed with fuel or injected in to the combustion chamber with the fuel.  The long term goals for two stroke engines have been to reduce the amount of oil used in mixes and to reduce the amount of emissions containing the unburnt oil while increasing engine life.  

As two stroke engines continue to move to higher cylinder temperatures and increased compression ratios to improve performance, it’s critical to use oils that meet TC-W3 specs.

How are TC-W3 oils tested

From the NMMA, “The TC-W3® oil standard is a performance-based qualification program. The requirements include various bench tests for fluidity, miscibility, rust, compatibility, etc., as well as engine tests to evaluate the prevention of ring sticking and carbon buildup on pistons and other engine parts. The engine tests include one Johnson 40 hp and two consecutive Mercury 15 hp tests, all of which are run under severe conditions for 100 hours each. Two additional engine tests are also conducted to ensure a high level of lubricity performance.”

Why is this important

These specific tests and criteria are needed because of the high loads, high speed, exposure to high levels of humidity and salt water found with marine engines. Most standard oil tests don’t work for these conditions. So tests for oils specific for the marine environment are important for the current and future development of marine oils.

Why use AMSOIL marine motor oils

AMSOIL is known as the leader in the Synthetic Motor oils.  They have been developing, producing and pushing the limits of synthetic motor oils for over 45 years.  They take their research and real world data from their involvement in automotive, racing, marine and other industries to improve all their products.  Now, AMSOIL also has research from one of the most demanding industries, Wind Turbine gear box oil, to add to their line up. In addition to all the testing for API/NMMA and other industry certifications, AMSOIL has independent lab testing and conducts real world field studies of its products in use. They then publish the results of these studies for everyone to read.

Results of the Marine E-TRC engine study.
Test results of HP Marine oil in an E-TEC engine

Why this matters to you the marine engine owner

AMSOIL is the Factory Fill in over 50% of the gear boxes world wide for wind turbines.  When one of these gear boxes fail, it costs over $500,000 to repair or replace.  AMSOIL has had such great success in this market with reducing failures, that they are in talks to increase the number of factory fills they do.  What this does is gives AMSOIL amazing research and data, in one of the most demanding operating environments, to apply to the other oils they manufacture for other industries.  The harsh operating environments of marine engines being one of those other industries.

What marine oils are available from AMSOIL

For Four Stroke Marine Engines AMSOIL has Synthetic marine oils that provide the highest wear protection and great rust prevention for the high stress, high RPM and wet conditions of marine engines.  These protections last well into the storage season was well.

AMSOIL 10W-30 Synthetic Marine Engine Oil

NMMA FC-W (Cat) Certified
AMSOIL Marine Engine Oil SAE 10W-30

Is a premium synthetic formulation designed to withstand the heat and stress of high-rpm operation and deliver excellent wear protection. It protects against rust and corrosion during periods of inactivity and long-term storage to keep your engine protected, even when it’s not running. 

Applications include: Gasoline-fueled four-stroke inboards, outboards, inboard/outboards and personal watercraft, including those made by Honda*, Mercury*, Yamaha*, Johnson/Evinrude*, Bombardier/BRP*, Suzuki*, Nissan*, Tohatsu*, OMC*, Volvo-Penta*, Mercruiser*, Chevrolet* and Ford*.

Buy 10-W30 Marine engine oil here

AMSOIL 10W-40 Synthetic Marine Engine Oil

NMMA FC-W (Cat) Certified
AMSOIL Marine Engine Oil SAE 10W-40

Is a premium synthetic formulation designed to withstand the heat and stress of high-rpm operation and deliver excellent wear protection. It protects against rust and corrosion during periods of inactivity and long-term storage to keep your engine protected, even when it’s not running.

Applications include: Gasoline-fueled four-stroke inboards, outboards, inboard/outboards and personal watercraft, including those made by Honda*, Mercury*, Yamaha*, Johnson/Evinrude*, Bombardier/BRP*, Suzuki*, Nissan*, Tohatsu*, OMC*, Volvo-Penta*, Mercruiser*, Chevrolet* and Ford*.

Buy 10W-40 Marine engine oil here

25W-40 Synthetic Blend Marine Engine Oil

FC-W (CAT)®  Certified
AMSOIL Marine engine oil SAE 25W-40

Is designed with excellent shear stability to deliver a consistent lubricating film. It helps guard engine components from wear for maximum life. It is fortified with potent inhibitors that guard against damaging rust and corrosion.

Applications : Use in gasoline-fueled four-stroke inboards, outboards, stern-drives (inboard/outboards) and PWC that require any of the specifications, including those made by Mercury* and Mercruiser*. 

Buy 25-W40 Marine engine oil here

For two stroke equipment

AMSOIL Specifically designed for outboard motors, 2-Stroke Oil containing a heavy dose of low-temperature dispersant additives that excel at reducing varnish, carbon and deposit formation in water-cooled motors. They have low-smoke, low-odor, low-toxicity properties that produce fewer emissions, thus benefitting operators and the environment.

Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil

Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil

Designed for pre-mix applications as lean as 100:1 ratios or richer. Improves throttle response and lowers or eliminates smoke. Minimizes deposit formation and lowers emissions. Performance emphasis on the cooler operations of water-cooled motors.

Applications include: pre-mix use in two-stroke outboard motors, personal watercraft and jet boats that specify TC-W3. For maximum performance, mix with gasoline at 100:1 regardless of the mix ratio specified for the equipment. Richer mix ratios may be used where desired.

Buy Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil here

HP Marine Synthetic 2-Stroke Oil

HP Marine Synthetic 2-Stroke Oil

Excellent for Evinrude® E-TEC™ factory-lean setting (replaces Evinrude XD100™ 2-Cycle Oil). Helps prevent deposits, protects against wear, has low smoke, protects against rust and has low aquatic toxicity. Superior performance as an injection oil or at 50:1 pre-mix.

Applications include: Use in two-stroke marine applications that specify TC-W3, including those made by: Johnson/Evinrude*, FICHT*, E-TEC*, Mercury* EFI & Optimax*, Yamaha*, Nissan*, Tohatsu* TLDI*, Suzuki*, Mariner*, Force*. Use as injection oil or 50:1 premix (2.6 oz. per U.S. gallon of gas).

Buy HP Marine Synthetic 2-Stroke Oil here

As you can see AMSOIL, who has been a leader in all markets of synthetic motor oils, makes products for all manufacturers of  two stroke and four stroke marine engines.  These oils give you the best wear protection, rust prevention and longest lasting engines in the marine environment.  All of these oils are backed by AMSOIL’s industry leading warranty. 

AMSOIL Warranty
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***We remind you that it’s a violation of US Federal law for boat, engine and other power sport manufacturer’s to void your warranty or threaten your warranty for using the products you choose to use.

Trey

I am a retired Firefighter / Paramedic. I own 3 businesses. I own an AMSOIL Dealership and a Pet Safety Education business, where I am a certified Pet First Aid and Pet CPR Instructor. I also own a growing Dog Training Franchise with my wife, that we are expanding to open multiple locations. I enjoy working on cars and other restoration projects. I also enjoy spending time with my 3 daughters, teaching them to work on cars, hunt and fish.