The time frame for replacing engine oil varies by car, but in general oil should be replaced every 5,000 to 7,500 miles, advises How Stuff Works. Various factors such as the type of vehicle and driving conditions make a difference, so the vehicle's user manual provides the most accurate instructions.
The majority of automakers reject the recommendation to change the engine oil in a car every 3,000 miles, explains How Stuff Works. The 3,000 mile rule was initiated when engine oil was lower in quality. The motor oils used today do not break down as quickly or cause the buildup that previous oils caused, and don't need to be replaced as often.