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Low viscosity engine oils are considered a feasible solution for improving fuel economy in internal combustion engines (ICE). So, the aim of this study was to verify experimentally the performance of low viscosity engine oils regarding their degradation process and possible related engine wear, since the use of low viscosity engine oils could imply higher degradation rates and/or unwanted wear performance. Potential higher wear could result in a reduction in life cycle for the ICE, and higher degradation rates would be translated in a reduction of the oil drain period, both of them non-desired effects. In addition, currently limited data are available regarding “real-world” performance of low viscosity engine oils in a real service fleet.

This paper shows the results of a fuel consumption in-use comparison test where the effect of Low Viscosity Oils (LVO) was evaluated over a sample of 39 urban buses powered by Diesel and CNG engines. The aim of the test was to verify the fuel consumption benefits of LVO in Heavy Duty Vehicles (HDV) found in previous works, which were obtained mainly in engine test bench, when engines are working on “on-Road” conditions. In order to achieve this goal, a sample of 39 urban buses was studied over an Oil Drain Interval or 30.000 km (approximately an 11 month period), measuring daily mileage and fuel consumed to calculate each bus fuel consumption. Mileage was measured by GPS and fuel consumed was measured from refueling system. The sample was divided into two groups; a control group of buses using reference oils (SAE grade viscosities of 15W-40 and 10W-40) and a candidate group using LVO oils (SAE grade viscosities 5W-30).