Which grade engine oil for M800 1991 Type-I model? SF, SG, SH?

Please tell me which grade engine oil ie. SF, SG, SH is good for Maruti 800 1991 model which clocked over 90K. 

@Vndv94,

Have a look at the car's manual for info about the recommended oil. In fact if you visit any garage/car spares shop the people over there too will tell you which oil to put.

That said, since the car is so old, make sure that there are no leaks in it. Also, don't put fully synthectic oil without first verifying that the oil seals are fine and that there's no dirt/sludge actually in the seals - which incidentally will also work like the oil seals. Fully synthetic oil might dislogde this sludge making the engine actually leaky.

Anyway, I replaced mineral oil with Castrol Magnatec 10w40 which costed 1000/- for 3L and also changed Oil filter(MGP).  Now engine sound reduced and feeling more pickup. But engine is heating up more with castrol. When I did run engine idle for 20 mins the radiator fan is switching on more frequently as it was before oil change. Is normal? or should I change to Magnatec 20w50? plz help.

Good that the oil change has had a positive effect. If the temperature indicator stays just on or below the half mark then I guess things should be fine. However look out for any increase beyond that (even if not very frequently) in hot conditions or slow, heavy traffic - these are the times when the ambient temp. is higher and hence will show up any problems with engine cooling.

Also get the cooling system checked - adequate coolant (and correct mix of the same), clean radiator, no leaks, etc.