Originally Posted By: tig1
Originally Posted By: geeman789
0w20 is used by Subaru for one reason... fuel economy. And if you use 0w20 for the EPA testing, you are required to list it as the recommended oil grade...
Subaru has poor fleet CAFE numbers... they don't have a Yaris or Fit or Micra type subcompact in their line-up to boost the average... so they "require..." the 0w20 to eak out every tenth of an mpg...
The reasoning is that the 0w20 is slightly less thick when cold, so when the cold engine is started the oil pumps and flows with slightly less energy required, using less fuel as the engine warms up... which is true, but to a very small degree...
And once the oil reaches operating temps, a 5w20 is the same viscosity as the 0w20.
Warranty is the only issue when using the 5w20... most dealers ask for proof of oil changes, not proof of oil grade. Will a dealer play hardball if you use 5w20 and have a problem... ? Maybe, maybe not... but you won't know unless you have an engine issue under warranty... !
The OP quoted the owners manual and it says "for optimum performance and protection". That doesn't sound like fuel economy (CAFE) only is the reason for 0-20 oils. There's a lot more to using 0-20 than just economy.
The manual also says this:
Quote:
Engine oil viscosity (thickness) affects fuel economy. Oils of a lower viscosity provide better fuel economy. However, in hot weather, oil of a higher viscosity is required to properly lubricate the engine.
See 11-13 from the 2015 Subaru Outback owner's manual:
http://techinfo.subaru.com/proxy/91583/pdf/ownerManual/091583_2015_Legacy/MSA5M1504ASTISvD_16.pdf
-Dennis