Normally, the first thing mechanics do when an oil sample comes back out of spec is change the oil, which is cheaper than changing engines. But the economics of oil changes are not as simple as they used to be. Fleet managers are challenged to find better ways to reduce operating costs while increasing unit availability. Oil-disposal costs and documentation also burden fleet managers. An engine monitoring system and automatic lube system developed by Cummins Engine Co., Columbus, Ind., allows fleet managers to extend oil drain intervals while maintaining high lube quality, making an oil change a rare occurrence. The patented system uses proprietary electronic controls to monitor engine activity. Based on the vehicle's actual duty cycle, the automated valve draws used engine oil from the system and replenishes it with fresh oil, keeping contaminants to a minimum. Once drawn, the engine oil is mixed with the fuel oil and burned during normal combustion. Fleet managers can reportedly extend oil-change intervals to 300,000 miles for heavy-duty engines and to 4,000 hours for high-horsepower engines. They also can reportedly extend oil filter change intervals to 75,000 miles for heavy-duty engines and 1,000 hours for high- horsepower engines. Extending change intervals reduces labor, filter and oil-disposal costs, and is said to result in a two-year payback on an initial investment of $1,000 and four hours of labor for installation. Key words: engine, oil change, engine accessories, diesel