Fuel Economy Retention in Passenger Car Diesel Engines A Review of the First Test Development Undertaken by New CEC

It has been recognised for many years that specially formulated gasoline engine lubricants are able to improve vehicle fuel economy [FE] by a small but significant amount. Until recently these benefits have been evaluated using unaged oils, but increased interest in fuel economy resulting from the Kyoto Protocol and the continued use of the US Corporate Average Fuel Economy [CAFE] system have encouraged researchers to explore whether analogous effects are obtained in diesel engines and whether these benefits can be sustained as the oil is aged in normal service.

In this paper a test development completed within the restructured Coordinating European Council [CEC] [ref 1] using a Ford Duratorq 2.0litre diesel is described. It was found that fresh oil fuel economy performance improved when oils with reduced high temperature high shear [HTHS] viscosities were used and that performance was insensitive to friction modification. As the oils were aged an overall improvement in fuel economy occurred due to a prolonged running in effect tempered by a small oil degradation effect. This degradation proved almost insensitive to oil formulation. Consequently, for the Ford Duratorq engine with the selected test cycle and measurement technique, HTHS viscosity proved to be an adequate predictor of both fresh and aged FE oil performance. For this reason, it was decided that the development would not be progressed into a formal, commercially available engine test.