(1) Basics. Engine oil is the lifeblood of any engine. Its purpose is to absorb and carry away the extreme heat generated by engine components and clean the engine of contaminants by moving them to the oil filter. Engine oil also lubricates the metal-to-metal sliding parts. In the clutch, oil works to reduce heat and allows for the right amount of friction between the plates. Understanding engine oil helps you decide which oil to use and teaches you how to take care of it.

(2) Viscosity. The viscosity of a fluid is the measurement of its resistance to flow at a certain temperature. It’s one of the primary ways to describe an engine oil’s character. The higher the viscosity, the thicker the fluid. For example, heavy cream has a higher viscosity than water. Also, higher temperatures typically result in lower viscosity and vice versa. Lower-viscosity oils are beneficial for creating less drag and increased horsepower, but they can also break down easier and become detrimental over time. 

(3) Label. The Society of Automotive Engineering (SAE) came up with the viscosity test used by engine oil manufacturers. The American Petroleum Institute (API) and Japanese Automobile Standards Organization (JASO) each have standards for lubricants used in a broad range of applications. When an oil says that it meets or exceeds API and JASO standards, that means it passed the testing for their specifications. 

(4) Startup. The “10” in the standard 10W-40 engine oil label specifies the oil’s pump-ability at cold temperatures. To determine this number, the viscosity test is conducted at -25 degrees Celsius. A lower first number like “0,” which is a viscosity rating equal to water, is commonly used in vehicles operating in extremely low temperatures because it is crucial to move the oil quickly throughout the engine on startup so that the metal parts aren’t moving without their lifeblood of lubricating oil. 

(5) Multi-grade. The “W” on 10W-40 is thought by many to stand for weight, but it actually stands for winter. It means the oil is multi-grade and designed to work in cold and hot temperatures. Multi-grade oils have specific chemistry formulated to allow for a consistent viscosity in cold and hot conditions. 

(6) High temperature. The “40” in 10W-40 stands for the oil’s viscosity at operating temperature. This is tested at 100 degrees Celsius (212 degrees Fahrenheit) and is measured against the SAE J300 system, which uses centistokes (cSt) to describe the oil’s moveability. For example, a 10W-30 and 10W-40 engine oil have the same startup flow for the oil to disperse through the engine when it’s cold, but they have a different viscosity at operating temperatures. The 10W-40 is thicker when it’s hot. 

(7) Synthetic. Engine oils come in non-synthetic, semi-synthetic and full-synthetic forms. Non-synthetics are mineral- or petroleum-based and have a lower cost and lower quality. Semi-synthetics are a blend of petroleum and synthetic-based oils (with no definitive ratio for each), and they generally provide more stability than non-synthetic lubricants. Full-synthetic oils offer the most advantages in performance, longevity and cleanliness. 

(8) Car oil. Although a generic oil works in multiple applications, you should choose engine oils that are designed specifically for your motorcycle. This maximizes the performance and reliability of your engine. Passenger car oils are focused on fuel economy and long drain intervals. Plus, engine driveline components are installed and lubricated separately on cars, but they work as a single unit on a motorcycle, which requires the engine oil to compensate. Motocross-specific brands’ engineers focus solely on motorcycle applications and formulate their oils to meet specific performance criteria. 

(9) Maintenance. Engine oil prevents internal corrosion and is designed to keep any contaminants in suspension until the next oil change. This is why oil gets darker as it ages. Over time, the engine oil loses its ability to cool, clean and protect. Eventually, the oil is contaminated beyond the oil filter’s ability to filter out debris. The clutch can even start slipping prematurely if the oil hasn’t been changed, because the debris is causing the clutch plates to lose friction. 

(10) Transmission oil. The 2002–2016 model Honda CRF450s used separate compartments for the engine oil and transmission oil. It worked well for reducing friction and increasing power, because Honda owners could use specialized fluids to meet two separate needs. The downside was that the smaller quantities in the two compartments created less room for error. Honda rejoined the rest of the motorcycle manufacturers with its new model in 2017 that used shared engine oil for the crankcase and transmission.



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