Nine engine oils were evaluated in two GM vehicles: a 1993 Pontiac Grand Am with a 2.3L Quad4 engine and a 1993 Buick LeSabre with a 3.8L (3800) V-6 engine. Standard EPA (Environmental Protection Agency) fuel economy (FE), vehicle-dynamometer tests were conducted. The results were compared with the fuel economy obtained with a standard ASTM reference oil (BC). The vehicle data from this program were used in evaluating the new engine-dynamometer ASTM Sequence VI-A test designed to predict “real world” fuel economy in vehicles.
EPA 55/45 combined fuel economy performance in the GM vehicles ranged from almost 2 percent improvement (over the BC oil) for an SAE 5W-20 oil, to over 2 percent poorer fuel economy than the reference oil for an SAE 20W-50 oil. The two different engines responded similarly to the different oils and showed similar trends. Both engines showed increases in fuel economy (as measured with the BC reference oil) over the more than 16,000 km (10,000 miles) accumulated during the program. This increase in fuel economy is believed to be due to engine break in.
The fuel economy results could not be correlated to a high degree of significance with either kinematic viscosity at 100°C or HTHS viscosity. Although fuel economy tended to decrease with increasing viscosity (by both measures), considerable scatter in the data suggested that factors other than viscosity (differences in the frictional characteristics being the most likely) are important.
Sequence VI-A results correlated reasonably well with the vehicle results. Only one oil, ASTM FM-8, containing an extreme dose of a non-commercial friction modifier, did not seem to fit the correlation. This may be because the GM engines operate at higher temperatures than the Sequence VI-A Ford 4.6L engine. Overall, however, the data confirm the ability of the proposed Sequence VI-A test to predict fuel economy gains from engine oil for the “average” GM vehicle.