Most of the vehicle usage for average usage is based on frequent short trips, stop-and-go city traffic driving, driving in dusty conditions, and driving at sustained highway speeds during hot weather. For this type of driving, the recommendation is to change the oil every 5000 kms or six months. For maximum protection, most oil companies say to change the oil every 5,000 kms or three to six months regardless of what type of driving you do.

As vehicle accumulates more kms, more unburned fuel is dumped into the crankcase which dilutes the oil. This causes the oil to break down. So if the oil isn't changed often enough, you can end up with accelerated wear and all the engine problems that come with it (loss of performance and fuel economy, and increased emissions and oil consumption).

Regular oil changes for preventative maintenance are cheap insurance against engine wear, and will always save you money in the long run if you keep a car for more than three or four years. It's very uncommon to see an engine that has been well maintained with regular oil changes develop major bearing, ring, cam or valve problems under 150,000 kms.