Used in internal combustion engines, their major challenge comes from combustion products getting into the lubricant. Combustion products can oxidise the lubricant, forming harmful engine deposits. These deposits contaminate the lubricant, and, if left unchecked, ultimately impair engine operation.
Engine oil performance is judged on its ability to reduce friction, resist oxidation, minimize deposit formation, and prevent corrosion and wear.
Various institutes determine viscosity grades (SAE – Society of Automotive Engineers) and service classifications (API - American Petroleum Institute) for engine oils. Combined, these indicate overall performance levels.
Viscosity classifications assure easy engine starting and lubrication at low temperatures, and adequate lubrication at high temperatures.
SAE J300 engine oil viscosity
|
SAE viscosity grade |
Low temperature cranking viscosity, cP max. |
Low temperature pumping viscosity, cP max. with no yield stress |
Low shear rate kinematic viscosity (cSt)
at 100ºC, Min. |
Low shear rate kinematic viscosity (cSt)
at 100ºC, Max. |
High shear rate viscosity, cP at 150ºC Min. |
|
0W |
6200 at –35 |
60000 at –40 |
3.8 |
|
|
|
5W |
6600 at –30 |
60000 at –35 |
3.8 |
|
|
|
10W |
7000 at –25 |
60000 at –30 |
4.1 |
|
|
|
15W |
7000 at –20 |
60000 at –25 |
5.6 |
|
|
|
20W |
9500 at –15 |
60000 at –20 |
5.6 |
|
|
|
25W |
13000 at –10 |
60000 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) |
|
40 |
|
|
12.5 |
<16.3 |
3.7 (15W-40, 20W-40,
25W-40 & 40) |
|
50 |
|
|
16.3 |
<21.9 |
3.7 |
|
60 |
|
|
21.9 |
<26.1 |
3.7 |
Service classification matches the lubricant to the performance requirements of the equipment type.
Original Equipment Manufacturers (OEMs) also have specific performance requirements, which may be over and above these industry standards.