stick to what ever said in manual to be free from confusion!
and chainging oil and oil filter in advance is not a big sin. of course good for the car. btw
, i have heard that figo diesel uses synthetic oil and change interval is 15k kms. ?
For the manza its 20k kms or 1year. and it uses 5w 40.
5w 40 is synthetic and normally used in petrol as well as diesel.
i use a shell helix and elf sometimes wurth as both the distributors are my friend.
though presently my sierra runs on castrol gtx , it has become so black in just 2000 kms of run