Raza sb, actually, I was reading ur posts continuously but just now, I read an e-mail from our very own ahmad bhai. 
He asked me to elaborate a bit on the oils but lazy me, I read the e-mail 2 days later.
Sorry ahmad bhai... 
coming to the topic, bros, I don't have much knowledge over here but still, sharing what I've got so far.
As we are talking abt new cars over here, so bros, for a new car, the best oil to use is the one having greater viscosity. The reason is, it prevents most of the inevitable wear and tear inside. more viscous, more lubrication, and hence lighter the engine, the drive and the response.
The 'w' in the grades stands for 'winter' i.e the oil's viscosity has been measured at cold temperature, and the number that follows,stands for viscosity itself.
A 5w30 oil will be more viscous and temperature withstanding as compared to a 10w20.
In Pakistan, as we have high temperatures prevailing and very often, w come across situations where ladies move into shopping malls for countless hours and we have to wait in the car with AC on in idling. The oil comes in handy and keeps the engine cooool in this state.
But bros, its not the only thing that matters, the thing thats even more important than this is the brand, the quality of the oil u are about to use.
never buy anything that u have any ambiguity in, about its packing, quality, unbelievably low pricing, etc...
Its the oil that will make ur engine live long and strong after several thousand kms... 
I hope this helps a bit...
