Originally Posted by wemay
Originally Posted by LubricatusObsess
And if they don't say the customer must use those viscosities in their O&M Manual, EPA can void their certification for meeting CAFE regulations.
Do you have link to this information?
https://cen.acs.org/business/specialty-chemicals/Engine-oil-becomes-critical-automakers/97/i5
Quote
Over the decades, modifying these ingredients has yielded greater fuel economy. The preferred strategy for formulators and additive makers is reducing the viscosity of the engine oils.
"Viscosity is really drag," says Mark Sztenderowicz, global manager of product development for automotive engine oils at Chevron Oronite, the lubricant additive arm of the big oil company. "Moving a thicker fluid takes more energy. If you reduce viscosity, less energy is consumed in the moving parts and in pumping the fluid around the engine."
This strategy can be seen in the evolution of SAE International grades of oil, such as 5W-20. The lower the code numbers, the lower the viscosity. The number before the W—which stands for "winter"—signifies the cold viscosity performance; the one after it designates the viscosity of the oil after the engine has warmed up.
In the early 1990s, 20W-50, 10W-30, and 10W-40 were the most popular grades, Henderson says. Now the most common ones are 5W-20 and 5W-30.
Newer engines use 0W-20, 0W-16, and even 0W-8. How much fuel efficiency benefit comes with lower viscosity varies from engine to engine, Sztenderowicz says. But, for example, a change from a 10W-40 to a 0W-20 oil, assuming identical engines, could bring up to a 3% improvement, he estimates.
Rolling out such lower-viscosity products poses challenges, Sztenderowicz says. At lower viscosity, base oils are more volatile and likely to evaporate. Solving this problem necessitates higher-quality, and often more expensive, base stocks.
And the changes stretch beyond base stocks. "As you go to the thinner oils, you need the additives to work a little harder," says Cyril Migdal, head of global application technology for lubricant additives at the chemical maker Lanxess. "When there is less film thickness, there is a higher probability that engine parts can come into contact with each other. If they come into contact, you will have wear."
More and better additives—antiwear additives, for example—might be needed to protect the metal surfaces, Migdal says. And because thinner oils are more susceptible to oxidation, they require stronger antioxidants.