Gear oil is a special lubricant for transmissions and differentials in cars, trucks and machinery. Manual gearboxes and differentials use rather highly viscous hypoid gear oils compared to engine oils. Gearboxes do not have an oil pump, so the high viscosity is needed to distribute the oil and to keep it on the metal surfaces, as only the lowermost part of the gears is located in the oil sump.
Depending on the type, these oils contain different amounts of extreme pressure and antiwear additives. The viscosity grades of gear oils are specified according to the SAE Standard J 306. The API (American Petroleum Institute) divides gear oils into 6 classes.
Viscosity Table – Measurement data
SAE 75W-140
Temp. [°C]
Dyn. Viscosity [mPa.s]
Kin. Viscosity [mm²/s]
Density [g/cm³]
0
1551.5
1792.6
0.8655
10
768.20
894.09
0.8592
20
410.55
481.38
0.8529
30
236.53
279.38
0.8466
40
145.40
173.00
0.8404
50
94.468
113.24
0.8342
60
64.333
77.695
0.8280
70
45.654
55.561
0.8217
80
33.544
41.137
0.8154
90
25.409
31.399
0.8092
100
19.749
24.591
0.8031
Gear oil SAE 75W-140 - kinematic viscosity and density over temperature