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Ask The Experts | Four Cycle Engine Oil Update
Article courtesy of Yamaha Outboards

By now, youre probably aware that automotive lubricants arent adequate for use in your four-stroke outboard, and that you should look for marine-grade oils displaying the National Marine Manufacturers Association® (NMMA®) FC-W® (Four-Stroke Cycle, Water-Cooled Gasoline Engine Lubricant) certification label.

Have you ever considered what that FC-W® rating really means? We at Yamaha wanted you know because our findings gave us a new appreciation for all the behind-the-scenes work necessary to prove an oil is worthy of the FC-W® approval.

This gets a little techy but its great information so you use the right oil for your engine.

Dozens of Tests
Using the NMMA® FC-W® Certification Procedure Manual as the guide, a four-stroke oil must successfully complete tests in 12 major categories, including all the steps and tests within each of the categories, to be eligible for FC-W® certification.

Here are the categories and brief insights into the specific nature of the individual evaluations:

A. Identification Tests
Identification tests, using ASTM International standards, define the test oils unique characteristics, defining precisely what makes this oil different than other lubricants.

Note that 10 tests comprise the Identification portion of the FC-W® protocol.

Kinematic Viscosity @ 40C/104F (ASTM D445)
Viscosity Index (ASTM D2270)
Specific Gravity (ASTM D1298 or D4052)
Total Base Number (ASTM D2896)
Total Acid Number (ASTM D664)
Elemental Analysis (ASTM D4951, D4927, D4628 or D5185)
Sulfur Content (ASTM D5453, D2622, D4294 or D6443)
Nitrogen Content (ASTM D5291 or D5762)
IR Spectrum (ASTM E168)
SAE Viscosity Grade (SAE J300)

B. Kinematic Viscosity @ 100C/212F
Kinematic viscosity loosely translates into how thick the oil is, at a specific temperature, when moving (via gravity in the test). This test determines the oils thickness (viscosity) at 100C/212F by measuring how long it takes the oil to drip through a calibrated glass laboratory fixture.

C. Cold Crank Simulator Viscosity
As the temperature drops, oil tends to thicken and flow slower than it would at normal engine operating temperatures. This segment of the evaluation simulates the effects of low temps (-5C/23F to -35C/-31F) on an oils ability to provide adequate engine bearing lubrication when starting the engine in cold conditions.

D. MRV-TP1 Viscosity
Starting at 80C/176F, an oil sample is cooled to predetermined temperatures where oil failures typically occur. A complex rotor/stator fixture measures the oils resistance to turning motion, to determine how well the oil will flow through the engines oil pump at cold temperatures.

E. Foam, Sequence I, II and III
This test determines the foaming characteristics of lubricating oils at 24C/75.2F and 93.5C/200.3F by blowing air through the oil at specific temperatures. Foaming (air/oil mix) can prevent the oil pump from circulating the oil through the engine, resulting in lubrication-deprived components, and eventual engine failure.

F. Foam/Aeration, Sequence IV
Oil foaming at high temperatures creates a host of issues, including lack of internal component lubrication, inability of the oil pump to circulate foamy oil, as well as oil system overflow from the increased volume of foaming oil. Conducted at 150C/302F, this test quantifies an oils foaming characteristics and performance at elevated temperatures.

G. Shear Stability
Predicting the decrease in an oils viscosity when its polymer ingredients break down under shear stress indicates how the oil is going to perform in the real world.

H. High Temperature High Shear Viscosity
A key property of an engine lubricant is its High Temperature High Shear (HTHS) viscosity the ability of an oil to maintain sufficient viscosity at high temperatures (150C/302F). This indicates if an oil is likely to provide proper lubrication to critical parts of the engine, such as the piston ring-to-cylinder wall contact area, crankshaft bearings, connecting rod bearings, and camshaft bearings.

I. FC-W® Rust (Salt Fog Test/SFT)
Marine engines operate in a damp, wet environment it goes with the territory. The last thing we want is rust forming inside the engine; this test tells us how well a candidate oil protects cylinder bores from corrosion and rust.

J. Noack Volatility
As operating temperatures increase, lighter portions of an oils formulation are likely to evaporate, leaving behind thicker, heavier parts of the oil. The result is reduced engine performance and reduced fuel economy because of the extra effort required for the moving parts to slog through the remaining higher-viscosity oil. This exercise determines the lubricants evaporation rates at given temperatures to predict the oils performance in real life.

K. Filter Plugging (EOFT)
This test replicates running a new engine briefly, then storing the engine for an extended period, with a bit of water and combustion by-products suspended in the oil then, to what degree will the slightly contaminated oil clog up the oil filter when you restart the engine.

L. Yamaha 115 Hp General Performance Engine Test (GPET)
This separates the players from the wanna-bes our favorite test by far.

Using a brand-new Yamaha 115 hp four-stroke outboard (powerhead) outfitted with a cut-down propeller to simulate a load, the engine is run in a test tank at specific rpms for predetermined lengths of time.

Oil samples are taken at requisite intervals to monitor the oils dilution levels, and the engine is disassembled at the end of the test to inspect individual components for lubrication-related wear or damage.

And this is the condensed, easy-to-read version; each test is thoroughly documented to ensure only the best oils make the cut.

Every engine manufacturer has their own proprietary lubricant blends, and we strongly recommend using the lubricants specified in your engines owners manual.

Yamaha four-stroke outboards reach peak performance with Yamalube oils and lubricants, for example.

Dont cut corners and put lower-quality, non-certified oil in your four-stroke outboard. The few bucks you might save today can negatively impact your boating experience and your wallet in the future.

Get the best. Your outboard deserves it.

[EDITORS NOTE] Find the marine engine oil at

Article courtesy of Yamaha outboards. For additional information on Yamaha boating, visit

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