oil viscosity what's right
All the auto manufacturers are 'recommending' 0W30 to 0W50 in their new cars. the reason is simple Corporate Fuel Economy (CAFE) penalties. Lower viscosity oil means higher fuel economy in the EPA mandated test cycle. They HAVE to use the oil viscosity recomended in th emanual, and a specification that is 'readily available in the market area (no magic mouse milk exotic stuff allowed.) AND so long as the engines make it to the end of the warranty period, the manufacturers are happy. Same with tranny fluid. More and more 'new engines' and tranny's are wearing out these days from the low visc fluid not keeping lubrication sufficient when either a warm spell, or a high speed run on the highway happens.
Pitty the poor second owner who has to shell out $15-20K for a new engine when the cams and rods wear out.
In the lower 48, excepting the real 'arctic' places that get colder than -10F regularly, there is no reason to use anything lighter than a 10W40. 15W50 synthetic is great for anywhere except Edmonton or Fairbanks or other similar un-inhabitable frozen waste lands.
Only the 'miracle' of cheap petroleum products allows man to settle in those places and drive cars anyway.