10-40 is fine Bob - the other guy is the stupid one here.
Manufacturers have been recommending lower viscosity oil for years, more due
to regulatory concerns than engine life.
Honda now recommends 5-20 oil not to extend engine life but to garner tax
credits offered under the Clean Air Act of 1991 to increase corporate fuel
economy. Thinner oils increase mileage only negligibly in each vehicle but
the authors of the CAA (mostly democrats lead by George Mitchell of Maine)
felt this would save a lot of fuel overall. It simple did not, and
credible arguments have been made since that the thinner oil actually
reduces engine life.
And BTW the wonderful Clean Air Act also brought us MTBE gasoline additives
which have contaminated between 2000 and 3000 municipal water systems in the
Clean Air Act sounded so good at the time that every politician just HAD to
support that one!
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