# Understanding the Difference in Viscosity

#### FMC

Using Mobil 1 5W20 and 5W30 as the examples, how can I understand or gauge the difference between these two oil viscosity at the temperatures of 100 C

5W20 - Kinematic Viscosity @ 100 C, mm2/s, ASTM D445 = 8.6

5W30 - Kinematic Viscosity @ 100 C, mm2/s, ASTM D445 = 10

Is 1.4 difference between them a Large difference or a very small difference ?

I hope im explaining this correctly

At temperature, there are accepted ranges for 20 and 30 weight oils, as with the other weights. For certain applications, the higher MOFT of a 30 weight oil is advantageous, especially when shearing effects over time are accounted. Someone will post those ranges shortly, I'm sure. I don't have immediate access to them.

Being a thickie, I'd choose a 30 weight 7 of 7 days in a week.

There ... I kept my post short and with only one comment!

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At temperature, there are accepted ranges for 20 and 30 weight oils, as with the other weights. For certain applications, the higher MOFT of a 30 weight oil is advantageous, especially when shearing effects over time are accounted. Someone will post those ranges shortly, I'm sure. I don't have immediate access to them.

Being a thickie, I'd choose a 30 weight 7 of 7 days in a week.

There ... I kept my post short and with only one comment!
Dont worry i have arrived with the chart.

xW-20 = 6.9 - 9.2 cSt, >2.6 cP HTHS
xW-30 = 9.3 - 12.4 cSt, >2.9 cP HTHS
xW-40 = 12.5 - 16.2 cSt, >3.5 cP HTHS (0W/5W/10W-40), >3.7 cP HTHS (15W/20W/25W-40)
xW-50 = 16.3 - 21.8 cSt, >3.7 cP HTHS

= 8.6
= 10
Is 1.4 difference between them a Large difference or a very small difference ?
In real world terms, that's a tiny difference. Consider that most automotive engines have no active method of oil temperature control. The viscosity varies wildly over wide temperature swings. A cold day may result in oil temps of 180 and a hot day and heavier loads, 220f.

Now, take a look at the viscosity graph.