Engine Oil Sensors & Extended Drains

When on-board engine oil sensors became popular features on certain new vehicles in the late 1990’s, many predicted the demise of fixed, low-mileage oil drain intervals. Since that time, oil sensors have proven their worth and are standard equipment in all new Mercedes-Benz U.S. vehicles, as well as almost 90 percent of new GM vehicles. However, fixed 3000-mile drain intervals still seem to be the norm.

Some major car manufacturers have made no steps to incorporate oil sensors in their new vehicles. According to Jeff Jetter of American Honda, “We haven’t installed sensors in our vehicles here or in Japan. The drain interval issue is important and we look to our owner’s manuals to guide our customers.” In addition, since much of the aftermarket oil change world continues to recommend 3000-mile drain intervals, flexible drain intervals are not likely to become mainstream in the near future.

One criticism of on-board oil sensors is that many do not measure the actual condition of the motor oil, relying instead on monitoring engine revolutions, operating temperatures, driving speeds and other proxy measures to determine when to illuminate the “Change Oil Soon” light. However, relying on this information is not 100 percent accurate, especially for vehicles running higher quality oils capable of extended drain intervals.

In explaining his company’s drain interval recommendations, Bob Olree of GM says, “We’ve raised some of our maximum drain intervals to between 10,000 and 15,000 miles. In Europe the drain interval is around 30,000 kilometers, which is about 15,000 miles.” However, Olree adds, “We don’t put the maximum drain interval in the owner’s manual and let the monitor speak for itself.”

DaimlerChrysler’s version of the oil monitor system is called ASSYST in Europe and the Flexible Service System in the United States. While also making use of a computerized system to measure engine operating conditions, it also incorporates a special dielectric sensor in the oil pan that measures the changes in the capacity of a condenser as a proxy for the amount and type of contaminants present in the oil.

ASSYST is standard on all new European Mercendes-Benz vehicles. Klaus Land, of DamlerChrysler’s technical center in Germany, says, “our goal was to increase the oil drain interval for customers driving in good conditions – not short trips- and we achieved our goal. We continuously improve ASSYST and have had no problems with customer acceptance.

DaimlerChrysler’s technical center in Germany, says, “Our goal was to increase the oil drain interval for customers driving in good conditions – not short trips – and we achieved our goal. We continuously improve ASSYST and have had no problems with customer acceptance.”

Because Europe has several official standards of engine oil quality, while the U.S. only has one, European ASSYST systems allow better oil quality levels to be programmed into the system. “Initial programming of the ASSYST system is done at the end of the production line,” says Land. “However, better oil quality levels are set during maintenance visits for oil changes.”

In the United States, Mercedes-Benz vehicles powered by V-6 and V-8 engines are equipped with the ASSYST/Flexible Service System. According to spokesman Fred Heiler, “Our system will safely provide for longer maintenance intervals. The usual oil change and maintenance service, previously performed every 7,500 miles, is now done at a minimum of 10,000 miles depending on the type of driving and oil level. A clear, simple readout on the instrument panel tells the driver well in advance when the next service is needed.

“The key to an oil monitoring system is the algorithms and how they are programmed to reflect oil quality and driving patterns,” explains Dennis Florkowski, senior specialist and supervisor of DaimlerChrysler’s lubricants group.

“A central issue is a commitment to address auto maintenance and whether the target is extended drain intervals or simply to convince the driver to change oil when he’s supposed to,” says Florkowski. “Getting the driver to read the owner’s manual and the use of an on-board oil monitoring system are both part of the equation.”