The SAE J300 Engine Oil Viscosity Classification provides a standardized way to categorize oils based on their viscosity at different temperatures, helping consumers and manufacturers choose the right oil for specific applications and climates.
In 1911, the Society of Automotive Engineers (SAE) introduced the SAE J300 Engine Oil Viscosity Classification, a numerical code system designed to categorize motor oils based on their viscosity properties. This classification system aimed to provide both a standardized method for assessing an oil’s suitability for engine lubrication and a clear understanding for consumers.
Initially, the SAE J300 system comprised five numbered grades (SAE 10, 20, 30, 40, and 50), delineated by flow rates (viscosities) measured at 100°C. By 1926, this classification expanded to include six grades (SAE 10 through SAE 60). Recognizing the need to address performance in extreme temperatures, particularly cold weather conditions, the SAE introduced four “W” (Winter) grades in 1952, denoted as SAE 10W, 15W, 20W, and 25W, measured at -18°C (0°F). Subsequently, two additional low-temperature grades, 0W and 5W, were incorporated.
In response to issues observed in high-temperature operating conditions, particularly excessive wear under heavy loads, the early 1970s saw the integration of minimum High-Temperature/High-Shear (HT/HS) specifications, measured at 150°C.
By the 1980s, incidents of engine failures due to oil thickening in cold climates prompted further modifications to the J300 specification, necessitating cold temperature cranking and pumping tests.
A significant revision to the SAE J300 system occurred on April 2, 2013, with the introduction of a new high-temperature viscosity grade, SAE 16, addressing the need for lower viscosity oils to meet stringent fuel economy requirements set by passenger car Original Equipment Manufacturers (OEMs). However, this grade is not recommended for use in older engines or vehicles not designed for low-viscosity oils.
In addition to the inclusion of the SAE 16 grade, the 2013 revision adjusted the minimum viscosity limit for SAE 20 oils. Previously, the viscosity range for SAE 20 oils at 100°C spanned from 5.6 cSt to 9.3 cSt, with a broader range compared to higher-viscosity grades. To align SAE 20 with other viscosity grades, the minimum kinematic viscosity was raised from 5.6 cSt to 6.9 cSt. This adjustment aimed to optimize performance consistency across different viscosity classifications.
| SAE Viscosity Grade | Low-Temp (°C) Cranking Viscosity (cP) Max | Low-Temp (°C) Pumping Viscosity (cP) Max (with no yield stress) | Kinematic Viscosity (cSt) at 100°c Min | Kinematic Viscosity (cSt) at 100°c Max | High Shear Viscosity |
|---|---|---|---|---|---|
| 0W | 6200 @-35 | 60,000 @ -40 | 3.8 | ||
| 5W | 6600 @ -30 | 60,000 @-35 | 3.8 | ||
| 10W | 7000 @-25 | 60,000 @-30 | 4.1 | ||
| lSW | 7000 @ -20 | 60,000 @ -25 | 5.6 | ||
| 20W | 9500 @ -15 | 60,000 @ -20 | 5.6 | ||
| 25W | 13000 @ -10 | 60,000 @ -15 | 9.3 | ||
| 16 | 6.1 | <8.2 | 2.3 | ||
| 20 | 6.9 | <9.3 | 2.6 | ||
| 30 | 9.3 | <12.5 | 2.9 | ||
| 40 | 12.5 | <16.3 | 3.5* / 3.7** | ||
| so | 16.3 | <21.9 | 3.7 | ||
| 60 | 21.9 | <26.1 | 3.7 |
* For 0W-40, SW-40 and l0W-40 Grades ** For lSW-40, 20W-40, 2SW-40 and 40 Grades
SAE grade numbers are based on the kinematic viscosity range of an oil at 100°C. For instance, an oil with a kinematic viscosity of 10.4 cSt at 100°C is classified as SAE 30, as it falls within the 9.3 to 12.5 cSt range.
High-temperature viscosity grades have both minimum and maximum kinematic viscosity limits. In contrast, low-temperature (“W”) grades only specify a minimum kinematic viscosity limit. This is because “W” grades are determined mainly by Low-Temperature Cranking and Low-Temperature Pumping (apparent) viscosity, measured at specific temperatures and shear rates.
Apparent Viscosity (AV), usually measured in centipoise (cP), varies with shear rate and must be specified for accurate measurements.
Cold Cranking Viscosity (CCV) impacts engine startability in cold temperatures, with lower viscosities facilitating easier starts, reducing engine wear, and lessening battery strain. The Cold-Cranking Test, conducted with a Cold-Cranking Simulator (CCS), measures an engine’s ability to start under extreme cold conditions.
A Cold-Cranking Simulator measures an oil’s resistance to cranking in cold conditions, simulating the viscosity in crankshaft bearings during a cold start. This ‘apparent’ viscosity, reported in centipoise (cP), is measured at a specific temperature and shear rate, indicating the lowest temperature at which an engine is likely to start.
Cold Pumping Viscosity assesses an oil’s resistance to flow through the engine after a cold start. High viscosity can hinder pumping and cause cavitation. Ensuring proper lubrication during severe cold conditions is crucial to prevent engine wear.
The Cold Pumpability test, conducted 5°C colder than the Cold Cranking test, ensures the oil can reach the bearings. This viscosity is measured using a Mini-Rotary Viscometer (MRV).
In this test method, oil is cooled slowly through a wax crystallization range, then rapidly to the final test temperature. The resulting ‘apparent’ viscosity is measured in centipoise (cP).
Failures in this test correlate with real-world pumpability issues, often due to the oil forming a gel structure, leading to high yield stress or viscosity.
High-temperature/High-shear (HT/HS) Viscosity, measured at 150°C, assesses an oil’s ability to retain viscosity and resist shearing under high load and temperature conditions. Oils that thin out too much under these conditions may not protect engine parts adequately.
An oil’s film thickness can be significantly affected by high temperatures and shearing forces, causing the oil to lose its load-carrying ability. As shear rate increases, oil viscosity decreases (shear-thinning).
The HT/HS Viscosity test measures the apparent viscosity of oil at high shear and temperature using a High-Temperature High-Shear Capillary Viscometer, with results reported in centipoise (cP).