I have very reluctantly been watching my odometer climb, and when it hit 135,000 miles, my stomach churned. My auto-repair shop made it clear that I would need a tune-up at 135,000, but in my world, "tune-up" was code for spending a thousand dollars on parts I can’t comprehend. So I decided to read up on what other local writers are saying about regular engine maintenance. I learned about potentially dangerous fixes, like the driver's belt and cracked steering boot, but also that a tune-up can make cars more eco-friendly. In my case, my car was leaking oil, but other tune-ups might reveal a faulty oxygen sensor, worn spark plugs, or a dirty air filter---all which can cost a driver three to four miles per gallon. I also learned that oil can make a difference when it comes to gas mileage. Synthetic oils, for example, can improve your fuel economy, though they cost more up front. If you’re looking to make your car even more environmentally sound, check out Boulder’s Green Garage, which just opened last November. They call their mechanics "Carhuggers," offer a "green" oil change, and feature biodegradable engine and fuel additives.