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Compressed natural gas (CNG) is a promising alternative fuel due to several main reasons, specially the strict engine emission regulations all over the world. This has made that lot's of cities have decided to use CNG as an alternative fuel in their urban transport fleets or in other urban tasks. Nevertheless, due to the recent implementation of the CNG technology in automotive sector, several problems related to lubrication have been detected, mostly affecting a reduction of the oil drain period and these problems showed no relationship with a particular fleet nor with the lubricant's brand used. These effects will have a very important weight on fleet manager's decision to select CNG as an alternative fuel, thus this reduction does not only increase the cost in engine oil, there are other maintenance actions referred to this basic period of oil drain, thus also increases other more significant costs.

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.

One of the most interesting alternatives to reduce friction losses in the internal combustion engines is the use of low viscosity engine oils. Recently, a new engine oil category focused fuel economy, has been released in North America encouraging the use of these oils in the heavy-duty vehicles’ segment. This paper presents the results of a comparative test where the differences in fuel consumption given by the use of these oils are shown. The test included 48 buses of the urban public fleet of the city of Valencia, Spain. The selected vehicles were of four different bus models, three of them fueled with diesel and the other one with compressed natural gas (CNG). Buses’ fuel consumption was calculated on a daily basis from refueling and GPS mileage. After three oil drain intervals (ODI), the buses using low viscosity engine oils presented a noticeable fuel consumption reduction. These results bear out the suitability of these oils to palliate engine inefficiencies.

Due to the increasingly stringent emissions standards in the world and, on the other hand, the foreseen shortage of fossil fuels, the application of low viscosity engine oils (LVO) is considered one of the most interesting options for counter these threats. In parallel to a fuel consumption fleet test, the aim of this study was to assess the performance of commercial low viscosity oils regarding their degradation and engine wear, since the use of LVO could imply an increase in wear rate. Potential higher engine wear could result in a reduction in the expected engine life cycle, obviously is a non-desired effect. In addition, currently limited data are available regarding “real-world” performance of LVO 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).