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Evaluation of the fuel economy characteristics of engine oils requires a rigorous test design. Side-by-side test designs, though adequate for evaluating the control of deposits, wear, and viscosity, require too many cars for precise fuel-economy testing. Crossover, Latin-square, and other balanced-block designs cannot be used if the fuel economy oil shows “carryover” effects; that is, if the engine is conditioned by the fuel economy oil so that subsequent oils still show a residual fuel economy benefit. The most suitable test design is a sequential one. The reference oil is run until it demonstrates a constant level of fuel economy. The test oil is then run for enough miles so that its full effect has been reached. The comparison is made between the two stabilized levels. Examples are given for an SAE 10W-40, API SF oil, which showed a 4+ % fuel economy improvement in both fleet and EPA type chassis-dynamometer sequential-design tests.

An important quality feature of a crankcase engine oil is its ability to control oil consumption. To the average motorist low oil consumption is synonymous with the oil maintaining good engine performance, low levels of engine wear, low running costs and a clean driveway. In the current environment it has assumed major importance because of the possible adverse effect of oil consumption on exhaust emissions. An oil controls oil consumption by both its chemical and physical properties. Additive chemistry helps by minimizing piston ring and cylinder bore wear including bore polishing, the prevention of piston ring sticking and ensuring oil seals continue to work effectively. Tests to ensure control of these hardware variables were developed during the early 1980's. These test methods are briefly reviewed. Of the physical properties of an oil, viscosity and volatility are the two key characteristics known to affect oil consumption.