Low temp viscosity crossover

[mjoekingz28]

When I look at company oil lineups, I probably always see a 10w-40 having a much more viscous 40C viscosity than a 10w-30. So my question to you, is do they ever overlap?

Say a cold start with a 0w-40 versus a 5w-20?

Maybe a 5w-40 and a 10w-30.


it seems in these charts I read on company webpages state that the second number does ndeed correlate with the first #.

 

[Shannow]

The "W" ratings are pumpability and crankability at extremes of temperature.

They, and the 40C numbers have no correlation at all.

What correlation that does exist is 40C, 100C, and Viscosity Index (which is the dimensionless number that describes for want of a better word the slope of the curve between those two points).

 

[Quattro Pete]

Originally Posted By: mjoekingz28
So my question to you, is do they ever overlap?

You can plug in the numbers and see how close or far apart they are:
http://www.widman.biz/English/Calculators/Graph.html

Not exactly a scientific tool, but for some general indication. It does not take into account the "W" number.

Quote:
Say a cold start with a 0w-40 versus a 5w-20?

The 0W rating is obtained by pumping test at -40C.
The 5W rating is obtained by pumping test at -35C.

So yeah, at -40C, the 0w-40 should always pump better. If the 5W oil could have passed the test at -40C, then it would have been labeled as 0W.


Quote:
it seems in these charts I read on company webpages state that the second number does ndeed correlate with the first #.

Not sure I follow.

 

[mjoekingz28]

Ok, thanks.

I just looked up a 5w-20 and its 40C was 48.

Then I looked at a 0w-40 and it is 77 at 40C.

I was thinking this is where the W weight is from and the 100C is where we get the second number.

Quattro Pete, I mean on the product information charts of a company's oil. I just never understood how a 5w-40 and a 5w-30 could have vastly different 40C viscosities when they are both 5w. I realize for the 40wt to be a 40wt it would probably not flow as well as low temps, but I couldn't understand how they could rate it the same. (As above)


If this is not clear QP, I will show you the chart I am referring to and share the thought process.

Basically, the 40 in a 10w-40 made the 10 a 'heavy' 10. While the 30 in a 10w-30 made the 10 a 'light' 10. I came to that conclusion since the 40C numbers were so different even though they were both 10w.


Thanks Shannow and Quattro Pete.

 

[Quattro Pete]

Originally Posted By: mjoekingz28
If this is not clear QP, I will show you the chart I am referring to and share the thought process.

Please post it.

Quote:
Basically, the 40 in a 10w-40 made the 10 a 'heavy' 10. While the 30 in a 10w-30 made the 10 a 'light' 10.

There is no heavy 10 or light 10. The number before the "W" is not a grade. It is just a winter rating based on cold cranking and pumpability tests. An oil either passes the test or it doesn't.

 

[dblshock]

wouldn't the 40C viscosity some what represent warm-up viscosity.

 

[umungus1122]

You would need to look at the exact oils and the exact temp. to find where they'd be the same. At say 50 degrees F for example, a 5w-30 is thinner than a 0w-40 usually, and a 5w-20 is usually thinner than a 5w-30.