It has been reported that multigrade oils save fuel and oil. In medium-speed diesel railroad engines, the claimed savings being about 20% oil and 1% fuel.Oil consumption in such engines has previously been measured in locomotives operating in commercial service, and subject to the errors and logistics problems associated with such procedures. We now report the results of an oil consumption test run in a full-scale engine on a dynamometer in a test cell.The technique involved estimation of the mass of oil in the engine by the amount of dilution of a pre-measured quantity of magnesium when added to the crankcase. This method accounts for oil in the entire system including the sump, filter housing, and oil galleries. The results indicated at least a 15% oil consumption benefit for an SAE 25W-40 oil versus SAE 40.The paper presents the technique, the mathematical model used, and a rigorous statistical analysis to support the conclusions.