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The following was extracted from 981443 - Extended Oil Drain Intervals - Conservation of Resources or Reduction of Engine Life (Part II)
"....The authors jointly presented a paper at the February 1995 SAE Congress (1). The main conclusion of the experience up to that time was:
"Used oil analysis of test cars in the European Market demonstrated that engine oils can be already exhausted at 6,000 km (» 3,700 miles) or could last up to 30,000 km (» 18,650 miles), depending on quality of the oil and use of the car....
"4. CONCLUSION
"For a considerable time it has been the objective for scientists and engineers around the world to optimise the use of resources on the one hand and on the other hand to reduce operational costs for cars by defining the ideal ODI. So far the best tools for the optimal definition of the ODI [Oil Drain Interval] are relatively simple engine calculation systems based on mileage, number of starts and average oil temperature.
"But also the oil quality has a major influence on the ODI. Since there is a wide variety of lubricants with different performance levels available in the market, it is necessary to develop a more intelligent system to include oil quality in the calculation.
"An important task is to detect the correct engine oil performance level. High performance engine oils are usually blended with extra high refined or synthetic base stocks at higher cost. But they have a range of benefits, especially reduced friction properties to improve fuel economy and emissions, reduced oil consumption and better wear protection properties. If this is also the case after several thousand miles of use, a bonus has to be included by calculating the ODI. On the other hand the ODI has to be shortened if a poor oil quality is used.
"But the ODI is not only heavily influenced by the quality of the engine oil, but also by the design and the use of the engine which are major influencing factors. Therefore ideally we have to develop on-board monitoring systems to detect the condition of the engine oil during its use. Sensors able to do so are under development, but not yet available for production.
"Combining the data stored in the engine management systems with "in situ" conductivity measurements is a step forward towards optimised ODI's. The experience and the high number of tests accumulated within the cooperation of both companies over several years resulted in the new ASSYST service system. With this system the car owners will benefit from an optimal mileage calculated up to the next oil change. But there will also be a cost benefit since the customer is able to select the most appropriate oil quality level (to benefit from high performance oils) and increase the lifetime of his car...."