How often should I change the oil in my compressor?

Because I only use my oil-lubricated air compressor in the shop for occasional fastening and blowing dust, I forget about changing the oil. How often should I be changing it?
—Randy Clark, Blacksburg, Va.

Great question, Randy, because regularly doing this type of maintenance extends the life and performance of your compressor. First, check your owner's manual for oil-change intervals. If you can't find the manual, a good rule of thumb is about 200 to 300 hours with conventional motor oil and 1,000 hours with synthetic oil. But if you live in a climate with cold winters, change the oil during the fall to a winter-grade (thinner) viscosity. (This holds true for job-site use, as well as in an unheated workshop.) Then change back to a summer grade in the spring.

While you're at it, consider any other tools and machines that use an oil-bath gearbox. Geared worm-drive or hypoid-drive portable circular saws typically require oil changes once a year. For oscillating spindle sanders, change the oil after 800 to 1,000 hours of use. Granted, that can be a long time for as little as you might use this machine in the shop. So, if you're not sure when you last changed the oil, you won't go wrong doing it once a year.