Machine shops use coolants to improve the life and function of machine tools. These coolants become contaminated with oils with use, and this contamination can lead to growth of anaerobic bacteria and shortened coolant life. The project investigated methods to extend coolant life through improved coolant maintenance, with the goal of reduced volumes of coolant waste. Skimmers to remove oil from the surface of coolants were found to be cost-effective. Use of a centrifuge was also tested. Coolant change practices were documented, and modified for improved coolant life. A specific coolant with wide applicability and tolerance was tested and found to have a life of at least seven months using the documented procedures. The work was performed between October 1, 1986, and April 30, 1988, through the Minnesota Technical Assistance Program and the Minnesota Waste Management Board.