This is my conclusion about the SAE J300 viscosity specification: It is obsolete and does not give the full picture.
SAE J300 was updated in the mid-1990s to correct inherent problems associated with it by introducing the HTHS viscosity, which is measure at 150 ℃ and a shear rate of 10⁶ s⁻¹. At that time, viscosity meters were limited to a shear rate of 10⁶ s⁻¹. However, the HTHS viscosity does not directly relate to engine wear.
Recently viscometers capable of measuring at shear rates of 10⁷ s⁻¹ have become possible. I introduced the HTFS viscosity, which is measured at a shear rate of 10⁷ s⁻¹ or higher (as shear rate → ∞).
The HTFS viscosity will determine the wear protection of an oil—higher HTFS for more wear protection. HTFS and viscosity index (VI) will determine the fuel economy—lower HTFS and higher VI for better fuel economy.
If my table is sorted by HTFS, you will see that some 0W-20 oils are thicker than some 0W-40 oils. For example, Ravenol ECS 0W-20 is thicker than M1 FS 0W-40. Therefore, before you get into any "thick vs. thin" debate, understand that the SAE viscosity grade does not paint the whole picture and a 0W-20 can actually be very thick.
HTFS and VII-content table sorted in decreasing HTFS
SAE J300 was updated in the mid-1990s to correct inherent problems associated with it by introducing the HTHS viscosity, which is measure at 150 ℃ and a shear rate of 10⁶ s⁻¹. At that time, viscosity meters were limited to a shear rate of 10⁶ s⁻¹. However, the HTHS viscosity does not directly relate to engine wear.
Recently viscometers capable of measuring at shear rates of 10⁷ s⁻¹ have become possible. I introduced the HTFS viscosity, which is measured at a shear rate of 10⁷ s⁻¹ or higher (as shear rate → ∞).
The HTFS viscosity will determine the wear protection of an oil—higher HTFS for more wear protection. HTFS and viscosity index (VI) will determine the fuel economy—lower HTFS and higher VI for better fuel economy.
If my table is sorted by HTFS, you will see that some 0W-20 oils are thicker than some 0W-40 oils. For example, Ravenol ECS 0W-20 is thicker than M1 FS 0W-40. Therefore, before you get into any "thick vs. thin" debate, understand that the SAE viscosity grade does not paint the whole picture and a 0W-20 can actually be very thick.
HTFS and VII-content table sorted in decreasing HTFS
HTFSV: High-temperature, full-shear viscosity
It is theorized that the wear for the following engine components depends on these variables among other things: Bearings: high-temperature, high-shear (HTHS) viscosity, TBN/TAN/base-oil oxidation performance (lead and copper corrosion) Piston rings: base-oil viscosity, TBN/TAN/base-oil...
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