@IIqbal
I use Zic A+ Fully Synthetic
When my car was only on Patrol then i used to change engine oil after every 2500 Kms exact...
But on CNG.. initialy I used to do that after every 2500 then 3000, 3500....
But since i m using Zic A+ .. i m doing it for every 4000 to 5000 Kms.
Note: I think we should change engine oil for every 3500 - 4000 kms to be on safe side...
Cuz I feel much difference in pickup and smoothness after changing the engine oil only.. i.e No Air filter, plugs change...
So it means after 5000 Kms the engine oil gets very thin or whatever and it can damage the engine i believe... cuz otherwise not much different should be there..
Regards,