Dear All,
Mineral Oils are Base Oils with some additives that do selective jobs like, cleaning, cooling, coagulation etc etc.(Tribology is a vast subject so lets not get into details). Since Mineral Oil is used, this oil on heating degenerates and forms carbon deposits after some time, the additives also become less effective etc etc. and so the need for change of oil.
Synthetic Oil on the other hand is manufactured totally artificially and is made to exactly suit the engine. Since this is not mineral based, it does not oxidise and generates carbon deposits very slowly so this oil can last sometimes about 7-8 times the life of a normal mineral oil. This depends on the quality of Oil.
I would suggest that one should go by the recommended grade of the manufacturer and change oil at given intervals.
By the way, since Mineral oils and Synthetic Oils are different altogether, most manufacturers recommend flushing. This may not be a ploy to generate extra income for the service center. Mixing of non compatible Oils may cause sludge formation and bigger problems. Please take a decision after consulting either your Car manufacturer/Service Center or pls ask the Oil manufacturer.
B