Engine oil change interval depends on a lot of factors, which include driving habits, climate, road conditions, load on the engine, acceleration/ deceleration ratios.... It's a huge list.
Owner's manual is normally a chappa kind of thing, which doesn't correlate with latest developments in petroleum products.
The best possible answer to this interval dilemma is by checking the dipstick once every month and noticing the smell and colour change.
Fully synthetic engine oils can last from 10-20k Kms on the odo.
The change intervals being quoted in the manuals or by mechanics is more of a marketing gimmick, however, to always remain on the safe side, 5000 km or 6 months is a decent change interval.
Something under this threshold is waste of money.
Then comes the reliability factor of oil brands. People run after Liqui Moly and Mobil 1, since these are packed at their respective plants abroad and do not allow local blends.
You can search on the internet and compare 2 different oil specs. I did the same for Total Quartz 9000 SN 5W-30 and Liqui Moly Special Tec AA 5W-30.
The entire data sheet was same for both the oils except one odd difference. The price difference is of Rs 4000. Why waste money over something !
