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.