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etrucker …
According to Matt Ansari, heavy-duty automotive manager at ChevronTexaco Global Lubricants, “With the advent of Group II base oils made with Chevron Isosyn technology, these impurities, which used to consist of at least 10 percent of the base oil, have been reduced to less than 1 percent. Once the oxidation problem was resolved, it became almost impossible to distinguish between synthetic oils and mineral oils in terms of fighting the hostile environment in an engine.”
Cherillo agrees. “If you refine mineral oils enough, they resemble synthetics,” …
Chevron research compares the performance of Chevron Delo 400 15w40, made from Group II base stock, with a 5W-40 synthetic oil; oil changes were made at 45,000 miles. It shows the mineral oil performs as well as or better than the synthetic oil in fuel economy, oil condition (including viscosity) and engine wear.
… it’s clear the most highly refined mineral oils now have a much greater resistance to extreme temperatures than in the past.