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In a previous paper (SAE 951035) Daimler-Benz and Shell advocated that fixed oil drain intervals should not exceed 15,000 km or annually. This paper describes further experience, with data from various field trials and engines, allowing engine condition to be considered in relation to lubricant ageing and condition. Based on this Mercedes-Benz have introduced ASSYST, a new passenger car maintenance system which processes customer-specific operating data and calculates oil change intervals. Unnecessary oil changes are avoided, conserving resources, and changes are not overlooked assuring durability. Intervals between 15,000 and 30,000 km are enabled, corresponding to between 1 and 2 years, representing a time extension of about 50%. Premium quality oil permits a longer interval, thus the customer sees an immediate benefit. This study shows that lubricant continues as an important engine design element and illustrates the environmental commitment shared by both companies.

The Quality-Level-Temperature-Sensor (QLT-Sensor) provides the dielectric number, level and temperature of fluids used in passenger car engines e.g. engine oils. The diellectric number can be used to indicate changes in oil-quality. Level detection can be used to determine oil corrsumption, minimum oil level or critical overfilling. The oil-temperature can be used in combination with the dielectric number for precisely predicting the oil drain time. The design-principles and functions including compensation of aging and temperature effects are described. It is shown, what engine constructors and developers must consider when regarding mechanical and electrical interfaces.