Predictive Maintenance Services, Inc.

 

Viscosity is a measurement of a lubricant’s resistance to flow.  It is commonly thought of as how “thick” the oil is - the higher the viscosity the “thicker” the lubricant.  Most laboratories report viscosity in centistokes (cSt) known as Kinematic Viscosity.  The lubricant type dictates the temperature at which the test is performed.  These charts of viscosity specifications are for NEW oils. 

 

Viscosity may be the most important and least respected indicator of lubricant health.  Changes in an oil’s viscosity are significant and should not be taken lightly.  A few of the more common causes of significant changes in viscosity are oxidation, degradation, soot loading, water, fuel dilution, shearing and incorrect make-up oil added to the system.

 

Viscosity Index

 

Viscosity Index measures the change of viscosity with temperature.  The higher the viscosity index, the smaller the relative change in viscosity with temperature.

 

 

ISO Viscosity Grade

Viscosity @ 40°C

22

32

46

68

100

150

220

320

460

680

1000

1500

Minimum cSt

19.8

28.8

41.4

61.2

90

135

198

288

414

612

900

1350

Maximum cSt

24.2

35.2

50.6

74.8

110

165

242

352

506

748

1100

1650

AGMA

Grade

 

 

1

2

3

4

5

6

7

8

8A

 

 

 

SAE Viscosity No. Crankcase Oil Viscosity

Viscosity @ 100°C

0W

5W

10W

15W

20W

25W

20

30

40

50

Minimum cSt

3.8

3.8

4.1

5.6

5.6

9.3

5.6

9.3

12.5

16.3

Maximum cSt

No

Req.

No

Req.

No

Req.

No

Req.

No

Req.

No

Req.

<9.3

<12.5

<16.3

<21.9

 

 

SAE Viscosity No. Gear Lubricants

Viscosity @ 100°C

75W

80W

85W

90

110

140

190

250

Minimum cSt

4.1

7.0

11.0

13.5

18.5

24.0

32.5

41.0

Maximum cSt

No

Req.

No

Req.

No

Req.

<18.5

<24.0

<32.5

<41.0

 

No.

Req.