There is always difference in Theoretical and practical understanding..I have my own Lubricants Business...998cc three-cylinder K series ‘K10B' engine is fitted in Wagon R ..that is offering power of 68ps @ 6200 rpm and torque of 90nm @ 3500 rpm.There are different recommendations for the oil grade for this particular engine..even Suzuki Maruti Recommends different grades even 15W-40 Synthetic oil depending on temperature difference..Ow-20 and Ow-40 can be put but i do not recommend it...even if recommended by the company..I normally put 5w-30 Fully synthetic oil for small engines even with latest Technology(While considering Pakistan overall environment conditions)..I had discussion with shell company ..even they don't allow these grades for smaller engines..There are different experiences i know especially in Mira after putting 0w-20...the engine sound was very much changed..thats why its better to remain in middle one ..Baqi everyone has different understanding depending on experiential + Theoretical Knowledge!