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Bench tests are often less expensive and faster than vehicle tests. However, correlation between bench tests and the engine needs to be proven, otherwise bench tests may be misleading. This investigation explored the relationships between bench wear test results and engine results from short-trip driving tests for a variety of conditions: fresh vs. used oil, different methods for assessing wear, and chemical effects such as oil contamination and differences in the fuel. There was a negative correlation between bench tests with fresh oil compared to vehicle test results with used oil, which suggests that bench wear characteristics of fresh engine oil should not be used to determine engine wear rates under the conditions tested here. Statistical analysis of bench test wear rates with used engine oil, compared to engine wear measurements, indicated that the trends were in an appropriate direction, with some scatter in the results.

The results of several investigations indicate the extent to which driving cycle, oil formulation, and fuel type (either regular unleaded gasoline or M85) influence the nature and severity of engine-oil degradation and engine damage. Driving cycle greatly influenced mass loss of piston rings and main and connecting rod bearings. For example, short-trip, cold start service with M85 caused 80 times more wear of top piston rings per km of service than was observed in long-trip service with the same oil. The magnitude of engine oil degradation was also documented. Under freeway driving conditions, in which the engine oil warmed completely, service with M85 fuel caused approximately the same amount of oil degradation as was found with gasoline. In city service, several engine oil parameters (base number, accumulation of insoluble contaminants, viscosity) degraded twice as fast with gasoline as with M85.

Extending engine-oil-change intervals is of interest from the standpoint of reducing used oil disposal and reducing time and expense of maintenance. However, the oil must be changed before serious oil degradation and engine damage occur. Three variables which influence oil degradation were chosen for investigation: base oil composition (synthetic oil versus mineral oil), trip length (short trips versus long trips), and driving schedule (degrading an oil during a given type of service, then changing to another type of service without an intervening oil change). Analysis of oil samples taken throughout the testing program indicated that type of service (freeway compared to short trip) influenced oil degradation to a greater extent than oil type. That is, API SG-quality synthetic oil in short-trip service degraded faster than borderline SG-quality mineral oil in long-trip service.

Accumulation of fuel, water, acids, insolubles, and metals in engine oil is documented and compared for variable-fueled (fuel containing up to 85 percent methanol) and gasoline-fueled vehicles in short-trip service. The oil temperature at which various contaminants are removed is noted. As a consequence of emulsion formation, the viscosity of the oil in the M85-fueled vehicles increased. Due to the presence of gasoline, the viscosity of the oil in the gasoline-fueled vehicles decreased. Equations were developed to explain both the viscosity reduction due to gasoline and the viscosity increase due to emulsion-forming contaminants (water and methanol).

Cold-start, short-trip driving causes the accumulation of fuel, water, and other contaminants in oil. In this type of service the engine oil degrades at a rapid rate. To gain a better understanding of the degradation, the oil under these conditions was observed and photographed through a transparent oil pan. In addition the oil was analyzed to provide a quantitative measure of the degradation. Oil analysis results confirmed what was observed visually; once oil became warmer, sludge and contaminants were removed, and many of the oil's properties (acid number, pentane insolubles, water in oil, etc.) improved.

To ensure that vehicles do not suffer adverse consequences when high-methanol-content fuel (M100 or M85) is used, it is important to understand the ways that the use of this fuel affects various vehicle systems. For that reason, some of the changes which occur in the engine oil when using methanol fuel were investigated. During a single cold start with an extended cranking time, as much as six percent fuel entered the engine oil. Over a 15-minute period, the lubricating medium changed from engine oil to an oil-methanol-water emulsion. With multiple cold starts followed by a five-minute trip and ambient temperatures near freezing, the oil contained 19 percent volatile contamination. In addition, the oil contained elevated levels of water, lead, iron, chromium, and aluminum. Efforts need to be directed toward reducing the adverse consequences of methanol fuel.

To insure maximum engine life, it is essential that engine oil be changed as required. Some drivers are not aware that the oil should be changed, and others do not know how often to change it. To assist the driver in this regard, an automatic oil-change indicator was developed. In developing the oil-change indicator, it was found that oil temperature, vehicle mileage, engine revolutions, and changes in the physical and chemical properties of the oil during use all provided an indication of oil degradation. Based on these measurements, a mathematical model was developed which relates oil life to oil temperature and either vehicle mileage or engine revolutions. Computer hardware and software suitable for use in a vehicle were developed based on the mathematical model. Vehicle testing, in conjunction with oil analyses, has confirmed the validity of the automatic oil-change indicator system.