Cp and Cst - the confusion between them

[Shannow]

Has been some confusion on the board, particularly when discussing the "Harman Index" as to Centipoise viscosity and Cst Viscosity.

Look at a J300 table (old now, anyone got a link to the new one with the 12s and 8s in it ???)

Cold cranking and HTHS are in Cp, while KV40 and Kv100 ... the former are called the "dynamic" viscosity, and the latter "kinematic". The dynamic, is the KV times the density at the test point.

What's the difference ?

Because a lot of SI units are based around fundamental properties of water, for a fluid of SG=1, they are the same...e.g. Engineering Toolbox conversion table but only when density is 1.

So if you are wanting to have cst equivalence of the CP viscosities, you have to divide the Cp by the density of the fluid at that temperature...To convert the cst to Cp, multiply by the density.

So to explain what was going on This thread

Originally Posted By: Shannow
Basically, use the KV40 and KV100 into the widman operational viscosity calculator, and calculate for 150C...multiply by density, and 0.885.


The 0.885 is the density corrector for 15C to 150C.

 

[Kuato]

This should be stickied somewhere.

 

[Garak]

Here and here are further mathematical discussions on the difference between the types of viscosity, along with more discussion of the units involved for those interested.

 

[widman]

Is the chart you want?

I don't remember If I've put it up in English. I've been busy re-writing everything to be mobile-friendly. Haven't gotten to the English side yet. (or fine-tuned the Spanish side).

 

[Shannow]

Yep with the 8 and 12*is what I was after

But the 40 grades no longer allow 2.9 hths

 

[widman]

If you have a different number, please let me know where it is. Everything I've got says 2.9 is for 0W-40 through 10W-40.

 

[OVERKILL]

Originally Posted By: widman
If you have a different number, please let me know where it is. Everything I've got says 2.9 is for 0W-40 through 10W-40.


1999:

vs 2009:

 

[Shannow]

Here's a link to the 2013 J300 which only has 16 added to it.

 

[widman]

I've got all of those. Jan 2015 is latest

 

[OVERKILL]

Originally Posted By: widman
I've got all of those. Jan 2015 is latest


As you can see then, sometime between 1999 and 2009, it went from 2.9 to 3.5 for the aforementioned grades.

 

[widman]

Thanks, now I see what I had missed. It is corrected, and since it is a link, it shows corrected.

 

[Shannow]