I have Maruti Alto LXI model car. its odometer 96000km. can I know whats the most suitable engine oil brand and grade for this??
As stated in the manual the recommended grade is 20W40 for that model and year.
Maruti Suzuki recommend various manufacturers oils - and offer co-branded versions under the following part numbers:
Shell Helix: 99999M20W40-SHL
Total Quartz: 99999M20W40-TTL
Any of those will do the job.
Technically, the right grade of oil for any engine is the thinnest oil which will develop adequate oil pressure after start-up. Oil pressure develops as the pump forces the oil against the surfaces the oil lubricates; the major contributors are the main bearings. If the engine's bearing tolerances are relatively tight, pressure will develop with a thinner grade of oil than they would with bearing tolerances that are loose. As the engine wears, the tolerances loosen, and then typically a heavier grade of oil is needed to develop adequate pressure. The grade specified by the manufacturer takes this into account, as well as known manufacturing tolerances and variations, and then attempts to achieve a compromise which will both satisfy a brand new, unworn engine, and one that has tens of thousands of miles/km on it. Since part of any motor vehicle manufacturer's goal is to improve/maintain their reputation for durability, an eye to this is given when specifying a motor oil. They also want to minimize warranty claims, and maximize fuel economy. Thicker grades of motor oil protect the engine better, but as they increase the work the pump must do, they tend to contribute to lower fuel economy.
In short, it's a compromise. Read more: https://www.machinerylubrication.com/Read/518/motor-oils