Originally Posted by slip_sinker

What’s your beef with 0w-20?


Probably just me being paranoid. 20 weight (and new 16 weight) oil is fractionally better for corporate average fuel economy ("CAFE") standards set by the government, but that does not mean that it is best for engine life. The first vehicle I purchased that spec'd 20 weight oil was my $17,200 2008 Honda Civic. That same year, high-end Ferarris and BMW "M" series performance vehicles were rolling off the assembly line with Shell Helix Ultra synthetic 10W-60 oil as factory fill. Am I to believe that my cheap Civic's motor was built to higher standards and "tighter tolerances" than a $400k Ferrari?

At that time I was a BITOG motor oil forum regular reader. Honda Accords being sold in the U.S. were specing 20 weight oil. Australian BITOG members posted pics of their Australian Accord owner's manuals with identical motors specing 15W-40 motor oil. If I lived in the American southwest, should I feel as comfortable running 20 weight oil as an Aussie living in the Outback running 40 weight oil? These examples also seem to refute the argument that the engineers who designed the vehicle know "which oil weight is best for the motor". Why would they have spec'd 20 weight in the U.S and 40 weight in foreign countries for the exact same motors? My guess is they were trying to meet ever-tougher CAFE standards.

Here is a link to a current website identifying which oils are approved by Mercedes Benz. Most are 40 weights, with a few 30 weights and 50 weights thrown in for good measure. None are 20 weights. I doubt my '08 Civic's motor is engineered to "tighter tolerances" than a modern six-figure $ Mercedes.

Mercedes Oil Specs

Chances are a motor will do fine with 20 weight oil, but I believe a thicker oil (at operating temps) of equal quality provides better protection, especially if pushed hard and/or in the heat. Modern heavier oils protect well at start-up, too. For the record, I run Mobil 1 0W-40 in my Civic, and it has 292,000 trouble free miles on the motor, and it's still going strong. The motor has never been touched other than to have routine maintenance.