Do you go by the old rule that a car's oil should be changed every 3,000 miles? New research by the automotive website Edmunds.com says changing oil that often may just line the pockets of the local mechanic. Oil chemistry and engine technology have come a long way — Edmunds found that car manufacturers recommended an average 7,800 miles between changes for 2010 models. That could save you $1,000 or more in five years. If your car has a built-in oil life monitoring system, a dashboard light appears when it's time to change. Otherwise, check your owner's manual.

Sid Kirchheimer writes about consumer and health issues.