Formulation Effects in a Severe Passenger Car Diesel Engine Test 2002-01-2678
The CEC-L-78-T-99 test, also known as the VW PV 1452 procedure, is a severe test of a lubricant's ability to prevent piston deposits and ring stick in a passenger car diesel engine. The test features in the ACEA “B” sequences and also, at a somewhat higher performance level, in various proprietary specifications. The demanding nature of the test means that it exerts a major influence upon the formulation of lubricants meeting these performance standards.
Passing this test with the SAE 5W-30 or 0W-30 grade oils needed for fuel economy can be a difficult task and obtaining satisfactory results from statistically designed experimentation can be plagued by instances of ring stick. A modified test procedure has been developed with the intention of avoiding the loss of data due to ring sticking. By stopping the test at intervals during the procedure, intermediate piston ratings can be obtained, this does not affect the outcome of the test. The modified protocol has been used to define the effect of viscosity modifiers and API Group III/IV basestocks on piston merit in a statistically designed experiment. Further work has produced a performance ranking of a series of Group III basestocks. The influence of dispersants on piston ratings has also been examined and the benefits of mixed systems identified.
An assessment of the interaction of the formulation requirements imposed by this test upon other performance features of the lubricants has been made. Low lubricant volatility limits are imposed by tests sensitive to oil consumption whereas low viscosity is favored to maximise fuel economy credits. Integrating these conflicting needs with the inherent piston deposit characteristics of the Group III basestocks studied provides a more rounded ranking of basestock performance.