Why a former powertrain engineer questions zero w 20 oil

The speaker suspects increasingly thin oil is partly responsible for engine failures he has seen discussed at GM, Toyota, and Honda, but does not establish that it caused those failures. He says the main reason manufacturers moved toward thinner grades is fuel economy: switching even from five w 20 to zero w 20 can yield roughly one or two percent savings. He argues that longer engine life is not the reason for specifying zero w 20 or zero w eight.

His strongest evidence comes from tests he ran at a domestic automaker in the mid 2000s. An overhead-cam engine that had existed for about 10 years was originally specified for five w 30, then five w 20. In durability cycles equivalent to 80 to 100,000 miles, engines tested with zero w 20 developed pitting on the cam and finger-follower rollers by about 80,000 miles; he says the five w 20 and five w 30 tests did not show comparable damage. The team consequently pursued harder roller and cam contact surfaces. This is his account of one testing program, not a comparison of today’s engines.

He disputes the claim that modern engines require very thin oil because their manufacturing tolerances are tighter: in his view, relevant parts have been made similarly for 20, 25 years. Cam phasers were present during his testing, and turbos dating to the 80s and 90s ran on five w 30 or 10 w 30. He also sees start-stop operation and cylinder deactivation as added stresses, especially alongside thin oil. As a specification contrast, he says his Honda Civic SI calls for zero w 20 in the US but five w 20 in other countries.

His practical suggestion is to use the specified thin oil in winter, but consider five w 20 instead of zero w 20 in summer; for his Honda, he plans that change in spring. He hopes it may prolong engine life, rather than claiming proof that it will. He worries that more engines struggle to reach 150 or 200,000 miles, and cites his son’s Toyota 86/FRS, with just under 100,000 miles, plus blown or replacement-engine listings he has noticed on Facebook marketplace. Those observations underpin his suspicion—not a demonstrated link—between its zero w 20 specification and failures.