10W-40 is totally wrong grade for 660cc engine. With 10W-40, the engine sound increases, fuel economy and acceleration decreases. Here's the recommendation from Suzuki Japan for R06A engine used in both Alto and Wagon R
You can clearly see the recommendation for R06A (NA) engine is 0W-20 grade. This is the same engine used in Pak Suzuki Alto. The point to ponder is the recommendation for TURBO version of same engine is 5W-30. Remember, the turbo engines produce lot more heat than NA engines. So the question is on what basis Pak Suzuki is recommending 10W-40 even though Suzuki Japan recommends 5W-30 for turbo engine.