On vehicle with flexible service interval, the service intervals are calculated, in addition to driven distance and time, also using fuel consumption and oil temperature. This calculation gives a value of the oil's degradation in relation to thermal loading. On vehicles with diesel engines the oil's degradation is calculated based on engine rpm, engine load, driven distance, and oil temperature. This gives values for thermal loading and soot deposits. Oil degradation is the decisive factor for when the next service shall take place. The shortest interval for service is 15,000 km or 12 months.