5w20, My .02

[acdaazn]

Originally Posted by dallas

The car calls for 5w30 whay would you use a 5w20, and shorten the life of your engine.
Using a 10w thinner oil is only worth around a .02 mpg improvement. Car mfg are using a lighter oil to meet CAFE ( corporate average fuel economy ratings). A car manufacturer must get a average fuel milage rating for their entire auto line or they pay millions of dollars in penalties. As the engine gets hotter the oil thins, thinner oil has less internal friction, hence better mileage, but under fast driving and high rpm the thin oil layer can be spun away so you have metal to metal contact. More important than the brand of oil you use is the oils viscosity. If you really want a lighter oil find a 5w30 that is lighter at 100C, or a 5w20 that is heavier than others at 100c All oil spec sheets will show the visc at 40c and 100c compare brands and find the right oil but in my opinion a 0-20 or 5w20 is just too light if you plan on keeping the car beond the warrantee period.

http://www.yarisworld.com/forums/showthread.php?t=5744

If they approve it, and it gives better MPG, why not? They "should" cover the engine with this grade of oil as well.