You might find some information here that will help you:
HPL has shared that unless your engine is burning or sending significant quantities of oil into the exhaust, there is no downside to running the Euro formulations.
Yes, rings have a harsh environment due to the high temperature seen in the ring pack, which thins down the oil even more in that region from the higher operating temperatures compared to the rest of the engine areas/components.
Not so much. Oils are formulated wildly differently. Most 5W-30 SN oils had HTFS in the range of 1.8-2.1. With SP, that’s now 2.1-2.2 to pass GF-6. In the case of HPL no VII, HTFS = HTHS. So 3.x…
Where does the ILSAC GF-x spec specify a minimum HTFS (Full shear) to pass? What oil specs actually define a HTFS spec to pass? And what ASTM and/or SAE spec procedure and test machine do they use?
HTHS is in page 155 here
I asked where is the official test for HTFS (Full Shear, not High Shear). And where is it a spec in any oil certification/license like ILSAC or API, etc with pass or fail criteria?
I know, HTFS is not mentioned anywhere obviously, there is even no standard test for it. Thats actually such a shame for an industry not to have an standard on such an important merit of their product.
The bold text in your post is why I made the comments I did in post 88 - I didn't think there was any spec of HTFS for any oil cert/license pass/fail criteria. I don't think knowing the HTFS is really that important - maybe it will be some day as oils become thinner and thinner, and if so maybe SAE J300 will incorporate it.
Even oils with no VII additive will have some shear thinning, and will have a lower HTFS than HTHS.
Apparently developing viscometers that can measure at very high shear rates is really challenging. Traditionally, viscosity at very high shear rates has been estimated with mathematical techniques, like those used in Ghokan's spreadsheet. A study from 1995 suggests that viscometer measurements at shear rates of 5x10^6 1/s were about as high as could be measured at the time. Some modern viscometers can measure accurately to at least 10^7. HTFS requires measuring viscosity at shear rates of 10^8. We may see a new standard at some point.
More or less true, but there are some outliers, especially some 0W-40s with high VI that don’t look so great on Gokhan’s old spreadsheet, even relative to their HTHS.
I don’t think the industry currently considers it a figure of merit. If anything, the industry is marching toward higher VI oils and lower HTHS for fuel economy. They are now designing engines to handle ultra thin oils, instead of before where the oils met the engine’s requirements.
And also going towards stronger AF/AW formulation as the oils become thinner to obtain a better tribofim strength for wear mitigation when the MOFT from viscosity fails. Viscosity has always been the main factor to keep moving parts separated, but the AF/AW tribofim is becoming a bigger factor to mitigate wear.
This is probably true for the nominal case where the bearings are assumed to never leave the hydrodynamic regime. There are engines that don’t always seem to be kind to their bearings and perhaps they leave the hydrodynamic regime for short periods. In those flawed designs or high load situations I would guess shear rates could exceed the commonly accepted range. For example, BMW specified 10W-60 with HTHS of 5.2 for S85 engines and they still ate rod bearings for lunch. The HTFS of that oil isn’t as good as the HTHS would suggest because of all the VII needed. Would a high HTFS oil help here? Not sure but I do wonder if HTHS is a good enough metric for the bearings in all cases.
One thing that most people don't realize with journal bearings is that the shear rate in the bearing, and also the resulting temperature rise of the oil inside the bearing is sensitive to not only the oil viscosity, but also the bearing clearance and MOFT thickness. If bearings are on the tighter side of their clearance range, it would decrease the MOFT to a degree. The smaller the MOFT, the higher the shear rate and the higher the temperature rise. The shear rate the oil experiences in the MOFT wedge can be drastically changed just by the thickness of the oil wedge, which is effected by the bearing clearance, oil viscosity and engine RPM. If things add up too much in the wrong direction with the balancing act, it can become a runaway situation. Tight bearing clearance is more sensitive and less forgiving than larger clearance. Also, low engine RPM with high rod load is bad for MOFT (ie, WOT at low RPM situations). Maybe the BMW issue was too tight of bearing clearance? I don't know, since I never studied the issue.
