supradjza80;1817248 said:
I just don't like to tell people something as FACT when I have no real information to back it up. I think it opens the door for you to look like an arrogant idiot if proved wrong which I try to prevent. Likely it is still a PAO oil and obviously it is just as good as always based on the Product data Sheet numbers.
One other question I have for you is the HTHS test results on this oil. I would expect this oil to perform a lot better in this test, 2.9 Cst is pretty low giving the oils Viscosity Index. Any thoughts on if this is an accurate number on the data sheet?
Like I said, I am very comfortable with my information. If you would like to prove me as an "arrogant idiot", please feel free to do so
Concerning HTHS (High Temperature, High Shear) - that test has to be taken in context for a specific oil. Some background:
- 100ºC viscosity is measured in centistokes (cSt) and represents the kinematic viscosity of the oil.
- HTHS viscosity is measure in centipoise (cP) and represents the dynamic viscosity or (more accurate) absolute viscosity of the oil. It is measured at 150ºC.
What we are looking at comparing the two is oil density vs shear stability at different temperatures. You can compare the cSt vs cP for two different oils with the same viscosity range, but never compare cSt to cP - they are apples to oranges. You can think of "cSt @ 100ºC" as resistance to flow through engine oil passages and "HTHS @ 150ºC." as resistance to flow between surfaces with a very small clearance (i.e. bearings, rings, etc). HTHS more closely approximates actual stress an oil encounters in a working engine than kinematic viscosity, but what we are really concerned with is does HTHS viscosity change (decreases) over time due to shear. So, looking at HTHS on a data sheet does not give the complete picture.
Higher HTHS is not necessarily better, it's only higher. Higher kinematic viscosity also isn't better, it's only higher. Higher HTHS means more viscous drag (power loss, more heat, lower fuel efficiency) - higher kinematic viscosity means more resistance to flow through the engine and generally will result in a higher HTHS through the bearings. So, you should choose the lowest HTHS that still provides the best protection for a specific engine - "better" depends on the engine that it's used in. It is worthwhile to compare kinematic to dynamic viscosity to get an idea of the shear stability for the oil.
Shear comes in two flavors:
- Temporary shear occurs when oil is under stress - the oil actually squishes/thins under compression, but recovers when stress is released.
- Permanent shear occurs when long-chain molecules in oil are actually cut and the oil permanently thins.
Shear stability refers to permanent shear. Multigrade oils with a wide viscosity range and high viscosity index (like a 15W-50) are more prone to permanent shear due to extensive use of viscosity improvers. You may find an oil with a high HSTS that actually shears more than an oil with a lower HSTS. It depends on the specific engine - you want an oil that meets minimum HSTS requirements and retains HSTS viscosity over time. The question is how to do this? A very simple way is to compare the relationship of kinematic viscosity @ 100ºC, divided by HT/HS viscosity @ 150ºC. Generally, the lower the ratio, the more shear stable the oil is. Take this as a rule of thumb - a kind of "blind" predictor
