Because it has uniform molecular size, Refinement, Additives which boost protection and can clean engines, Better function in cold and extreme weather and its cleaner oil with fewer impurities.
The benefits of synthetic oil vs conventional oil:
- Fewer emissions
- Better fuel and oil economy
- Increased engine protection and wear from lower friction
- Longer intervals between oil changes
- Reduced engine drag from greater resistance to thickening
- Oil effectiveness/quality is more predictable and uniform
- Better all-weather protection
- Quicker engine start time
- Helps clean engine sludge and deposits
(Source: https://www.idrivesafely.com/defensive-driving/trending/synthetic-oil-vs-conventional-oil
Lots of content is available on Internet. You can Google, if further details are reqd.)
In 5w-30, Total Quartz 9000 Future series 5w-30 is best for bucks, but do not drag it beyond 5,000 Kms. Change oil and oil filter after every 5,000 Kms.
However, if your oil filter can easily last 8-10K Kms, then changing it after every 5,000 Kms would be waste of oil filter. In that case, I would recommend Mobil1 5w-30 ( http://mal-eshop.com/mobil1.php?mid=149 ).
Bro, ZIC is also good as long as its 100% genuine and original.
I would suggest to avoid it. Its unnecessarily thick.
Bro, changing fully synthetic oil in normal driving conditions, after every 2,000-2,500 kms is a shear waste of money IMO.