Engine oil replacement interval is often given by the OEM which should be followed. But in many cases engine condition and the oil which is being used also determines the intervals.
First of all it should be noted that the mineral oil has lower mileage and drain interval. They should be changed after 3,000 km maximum. On the other hand, synthetic oil stays longer and in Pakistan all synthetic oil at least stay for 5,000 km to 20,000 km.
Factors and Conditions That “Shorten” the Oil Change Interval:
Short-trip Driving - The problem is most pronounced for frequent trips under five miles in cold wintertime conditions. Water and fuel have a tendency to accumulate in the crankcase when the oil temperature does not reach the thermostat setting.
Road Dust-Driving in dusty conditions (dirt/gravel roads) with an economy-grade oil filter can turn your motor oil into more of a honing compound than a lubricating medium. The dirty oil generates more wear metals which increase the risk of sludge formation and corrosion from acids
High-Mileage Engine - Engines with more than 75,000 miles generate more blow-by gases, un-burnt fuel and corrosive agents that enter the crankcase oil.
Diesel Engines - Diesels produce more soot and acidic blow-by products.
Flex Fuels - Alcohol-gasoline blends are prone to accumulate water in the crankcase.
Turbo-charged Engines - High temperatures distress the base oil and additives.
High Oil Consumption - While on one hand high oil consumption replenishes additives, on the other hand the affliction is also associated with high blow-by of combustion gases into the crankcase.
Hot Running Conditions - Hot running conditions, including desert terrain, in general can lead to premature oil oxidation, volatility problems and rapid additive depletion.
Desire for Long Engine Life - Shorter drain intervals increases the safety margin in the event of premature oil failure.
Towing/Heavy Loads generally relates to hot running conditions, thin oil films, higher shearing of viscosity index improvers and more wear metals in the oil. Wear metals catalytically shorten oil life, causing premature oxidation, sludge, acids and deposits.