When are service bike or car on service center? We are very confused about engine oil grade. Many companies provide the best engine oil with different grades 5w-30, 10w-30, 20w-30, and 20w-50. But what means of number.

Let’s clear about the means of these numbers. The first number is a temperature reading, the second is the viscosity rating.

Importance of Viscosity in Engine

The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine. The lower the viscosity the easier all this will happen. That is why cold starts are so critical to an engine because the oil is cold and so relatively thick.

But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft. The higher the viscosity, the better the load it can support. Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss, or increased fuel consumption. So a compromise is chosen to minimize power loss but maximizes load support.

Defines an Oil’s Viscosity

viscosity

SAE Viscosity Grades – Engines

SAE Viscosity Grades for Engine Oils (SAE J300) – December 1999
Absolute Viscosity (cP) Kinematic Viscosity (cSt) HTHS (cP) 150°C
Grade Maximum Cold Cranking Maximum Cold Pumping Minimum Maximum High-Temperature- High-Shear
0W 6 200 @ -35°C 60 000 @ -40°C 3.8
5W 6 600 @ -30°C 60 000 @ -35°C 3.8
10W 7 000 @ -25°C 60 000 @ -30°C 4.1
15W 7 000 @ -20°C 60 000 @ -25°C 5.6
20W 9 500 @ -15°C 60 000 @ -20°C 5.6
25W 13 000 @ -10°C 60 000 @ -15°C 9.3
20 5.6 <9.3 2.6
30 9.3 <12.5 2.9
40 12.5 <16.3 2.9 (1)
40 12.5 <16.3 3.7 (2)
50 16.3 <21.9 3.7
60 21.9 <26.1 3.7
Grade Maximum Cold Cranking Maximum Cold Pumping Minimum Maximum High-Temperature- High-Shear
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