In most instances of severe service, the recommended interval for changing oil is 3 months or 3,000 miles. When the engine is running, some unburned fuel and combustion byproducts are forced past the piston rings and into the crankcase where they are absorbed by the oil. As the engine wears, this blowby increases. Also, short trips combined with stop and go driving and excessive idling increase the contaminants. Motor oil contains detergent additives that neutralize the blow-by contaminants, but above 3,000 miles the detergents can begin to break down. Combustion creates dirt and contaminants in the oil and changing the oil is the only way to get rid of the contaminants.
If most of a vehicle’s driving is highway driving with little stop and go and synthetic oil is used, the interval for oil changes could be more like 5,000 to 7,500 miles, but most of us don’t drive under those conditions.
When we perform an oil change we include a 35 point courtesy inspection and set tire pressure to the vehicle’s specification.