Understanding the viscosity charts

[Dave Sherman]

Looking at the viscosity chart link off the main BITOG page, am I correct in reading from it that any 5W-xx oil at 40C has pretty much the same viscosity? I guess the real thing I'm trying to get at is: In bone biting cold, is a 5w30 going to be pretty much the same viscosity as a 5W-20 or even a 5W-40, and that the differences aren't really going to become apparent until it gets hot?

 

[d00df00d]

Viscosity is sort of a weird and complicated thing that can be measured in different ways with different results. The 5w measurement is taken differently from the 20/30/40 measurement, so the numbers are not necessarily comparable. Also keep in mind that 5w is a range, and a 5w-40 will usually (but not always) be higher in that range than a 5w-20.

However, the general idea you had is correct: all 5w-xx oils are similarly pumpable when cold, and all xw-20/30/40 oils are in the same viscosity range when hot.

 

[sangyup81]

the 5w is more for that pumpability test

@40c a 5w20 is in the 40-50 cSt range while a 5w40 is closer 10 100cSt

 

[mechtech2]

Dave - Yes, you are on the right track.
In temps around 0 deg F, those oil listed will be about the same.
In intermediate temps and hot temps, there will be differences.

 

[Dave Sherman]

Thanks all!