But where does the engine oil go?

Apart from massively polluting the air, 4-wheelers present another environmental problem -- the annual disposal of billions of litres of engine oil that need to be replaced every 4,800 km for cars and every 32,000 km for trucks. Engineers at the Florida-based TF Purifiner Inc, recently devised an oil-cleaning system which, when installed in trucks, made oil changes unnecessary for up to 640,000 km.

The canister-shaped system is connected to the engine's oil pressure sending unit. Engine oil first flows slowly through a replaceable cotton filter that removes particles as small as a quarter of those taken out by conventional filters. Then the oil is heated to 90.5oC to eliminate contaminants like fuel and water.