Determination of Lubricating Oil Additive Effects in Taxicab Service

A statistically designed field test was run to evaluate the effect of lubricating oil formulation variables on deposit control. The test duration was 160,000 km in midwestern taxicab service. The test engine was a 5.0 liter V-8.

Seven variables were evaluated in a 2^(7-4) highly fractionated factorial. The test was designed as a resolution III design to determine primary effects only. Variables included additive package composition, viscosity index (VI) modifier type, viscosity grade, and base oil. This matrix of oils spans the performance range from minimum API SG to next generation SG“+” oils. A low reference API SF and a commercially purchased API SG/CD oil were included for comparison.

The results of the test show that API SG oils provide a significant improvement in deposit control versus API SF oils. In addition, improvements in deposit control versus minimum level API SG oils were demonstrated. No difference in oil consumption was observed between the SAE 15W-40 and SAE 5W-30 grades in this engine and service. Comparisons between the field test results and the Sequence VE test are made.