I have recently bought Mira 13/16 and 90,000 km on the odo. The previous owner was using engine oil Amsoil 10w-40. I am not satisfied with this as the car is giving milage of 12 to 13 km in local and 16 to 17 on long. Can someone please suggest is this the right choice for my car?? If not then which brand & viscosity oil would you recommend?? And what should I do to increase its mileage??