Abstract: A number indicative of the number of engine revolutions corresponding to the useful life of the engine oil in a motor vehicle is stored in nonvolatile memory. As the vehicle is operated, the number is periodically decremented by an amount determined in relation to a penalty factor and the number of engine revolutions which occur in the period. The penalty factor is periodically updated and is determined in relation to the operating temperature of the engine oil, based on empirically determined data. The stored number represents the remaining life of the engine oil and is continuously displayed for the information of the operator. A warning lamp is lit to alert the operator to change the oil soon when the stored number is reduced to within 10% of the originally stored value. When the oil is changed, a reset switch is actuated and the number is reset to its original value.