The most widely used system for engine oil viscosity classification is that established by the Society of Automotive Engineers (SAE) in the USA.
SAE has established that twelve viscosity grades are suitable for engine lubricating oils.
The physical requirements for these viscosity grades are described in SAE J300, which is intended for use by engine manufacturers in determining engine oil viscosity grades suitable for use in their engines.
Currently low and high temperature viscosity requirements for these viscosity grades are shown below.
SAE Viscosity Grades for Engine Oils — SAE J300 Dec 99
|
SAE Viscosity Grade
|
Low Temperature Viscosities |
High-Temperature Viscosities |
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|
Cranking (cP) max at temp °C |
Pumping (cP) max with no yield stress at temp °C |
Low Shear Rate Kinematic (cSt) at 100°C |
High Shear Rate (cP) at 150°C min |
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|
min |
max |
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| 0W | 6200 at -35 | 60,000 at -40 | 3.8 | — | — |
| 5W | 6600 at -30 | 60,000 at -35 | 3.8 | — | — |
| 10W | 7000 at -25 | 60,000 at -30 | 4.1 | — | — |
| 15W | 7000 at -20 | 60,000 at -25 | 5.6 | — | — |
| 20W | 9500 at -15 | 60,000 at -20 | 5.6 | — | — |
| 25W | 13,000 at -10 | 60,000 at -15 | 9.3 | — | — |
| 20 | — | — | 5.6 | <9.3 | 2.6 |
| 30 | — | — | 9.3 | <12.5 | 2.9 |
| 40 | — | — | 12.5 | <16.3 | 2.9 (0W-40, 5W-40, 10W-40 grades) |
| 40 | — | — | 12.5 | <16.3 | 3.7 (15W-40, 20W-40, 25W-40, 40 grades) |
| 50 | — | — | 16.3 | <21.9 | 3.7 |
| 60 | — | — | 21.9 | <26.1 | 3.7 |
a) All values are critical specifications as defined by ASTM D 3244 (see text, Section 3).
b) ASTM D 5293
c) ASTM D 4684 (see also Appendix B and text Section 4.1): The presence of any yield stress detectable by this method constitutes a failure regardless of viscosity.
d) ASTM D 445
e) ASTM D 4683, ASTM D 4741, CEC-L-36-A-90
Grades with the letter W are intended for use at lower temperatures and are based on maximum low temperature viscosity and minimum high temperature viscosity at 100°C.
Grades without the letter W are intended for use at higher temperatures and based on the viscosity at 100°C only.
A “multigrade” oil is one whose low temperature viscosity and borderline pumping temperature satisfy the requirements of one of the W grades and whose viscosity at 100°C is within the stipulated range of one of the non-W grades .
Example :
- An SAE 40 (monograde) satisfies the SAE 40 requirement at 100°C i.e. Viscosity between 12.5
and 16.3 mm2/ s. - A 15W-40 (multigrade) satisfies the low temperature requirement for SAE 15W and
also the high temperature requirement for SAE 40 i.e. ASTM D2602 viscosity at -20°C is below
7000 cP and the ASTM D445 viscosity at 100°C is between 12.5 and 16.3 3 mm2/ s