Fuel economy is not an absolute attribute, but is highly dependent on the method used to evaluate it. In this work, two test methods are used to evaluate the differences in fuel economy brought about by changes in engine oil viscosity grade and additive chemistry. The two test methods include a chassis dynamometer vehicle test and an engine dynamometer test. The vehicle testing was conducted using the Federal Test Procedure (FTP) testing protocol while the engine dynamometer test uses the proposed American Society for Testing and Materials (ASTM) Sequence VIE fuel economy improvement 1 (FEI1) testing methodology. In an effort to improve agreement between the two testing methods, the same model engine was used in both test methods, the General Motors (GM) 3.6 L V6 (used in the 2012 model year Chevrolet™ Malibu™ engine). Within the lubricant industry, this choice of engine is reinforced because it has been selected for use in the proposed Sequence VIE fuel economy test. Results indicate that agreement between methods does exist for some oils. However in the case of ultra-low viscosity oils and oils containing high levels of friction modifier (FM) additives, the engine dynamometer test gave results much lower than those obtained in the chassis dynamometer testing. The consequence of this is that oils which may significantly improve vehicle fuel economy on the road may not be commercialized since the same benefit is not observed in the engine dynamometer test. Since the chassis dynamometer test uses a complete vehicle, is based on an actual drive cycle, and includes dynamic events such as transient operation and cold start, it is believed to be more representative of actual on-road vehicle performance than the engine dynamometer test. Further, chassis dynamometer testing provides a means to validate the relevance of the proposed Sequence VIE engine test results, including the benefits from highly friction modified and low viscosity oils.
