Viscosity Standards

While scales such as SAE or ISO try to standardize the classification of different lubricants and oils, the many different classifications and company-specific ratings mean that determining the viscosity of a product is confusing sometimes. Knowing how to read these standards and understanding what they mean for you is important when picking out the right lubricant. In general, a higher viscosity means slower movement, since the fluid resists flowing more strongly. This is also, in general, true of oil viscosity ratings; a lubricant that is SAE30 is less viscous than one that is SAE50. One exception is when comparing gear oils and engine oils — a 75W gear oil is roughly equivalent to a 10W engine oil. It is important to note that SAE viscosity classifications are also not 1:1, meaning 10W20 is not twice as viscous as 5W20.

A lubricant labeled SAExx, with xx being a number, is a single-grade oil. These are best used in applications with a narrow temperature range. One of the most common examples is SAE30 motor oil is often used for lawnmowers.

A lubricant labeled xxWxx or xxW-xx (used interchangably) are multi-grade oils.
These lubricants are more suitable for applications with a wide range of temperatures. The "xxW" part indicates the oil viscosity in cold, or winter, conditions.
The lower viscosity means that as the oil naturally thickens as it cools, engine performance will remain the same. The "xx" part indicates the oil viscosity at a high temperature. One common example is 10W30 motor oil, commonly used in everyday vehicles where the engine may be starting cold in the winter.

30WT, 60WT, and 70WT are mostly specific to Red Line Synthetic Oil's Race Oil line of products. In this case, 30WT is equivalent to SAE 10W30 and 60WT is equivalent to SAE 20W60. 70WT is equivalent to D-A Lubricant Company's PennGrade Nitro 70, or other SAE 70 lubricants. This engine oil is typically only used in extreme conditions, such as the ones found in drag racing competitions.

Overall, while it may not be readily apparent at first glance, most companies will try to align their specific ratings to be in line with SAE standards. Product data sheets contain more information regarding the viscosity and other characteristics of the lubricants for cases where that information may not be clear.