I had the oil changed on my Ford Freestyle last week, though the sticker on my windshield told me I was long overdue. What made me determined to get the oil change done quickly was the fact that near my odometer there is a “computer” screen that let’s me know how much “oil life” I have left, and as long as the oil life is below 10%, your odometer disappears and this message continues to blaze in your face. By the time I’d rolled in to the local gas station to get my oil changed, my oil life was at 1% and my odometer was nowhere to be seen. Whew, made it just in time.

I picked up the car a few hours later, paid my bill and drove off. It wasn’t until I was halfway home that I discovered that my oil life was still reading 1%. Thinking I’d been ripped off and that the guys hadn’t really changed my oil, I called the gas station in a tizzy. Guess what? When you change a car’s oil, the “change oil soon” or “oil life 1%” light doesn’t automatically go off once someone goes under the hood, sort of like your “empty” light from your gas tank goes off when you fill up. With oil changes, the mechanic has to manually reset it.

So I turned around and went back to the station. When I got there, I turned off the engine, popped the hood and hopped out of the car. I walked around to meet the mechanic at the front of the car, but he slid into the driver’s seat.

Turns out the “reset” button on my car isn’t under the hood but under the steering wheel. I’d never noticed before that there is a console of three buttons there: program, info and reset. The mechanic pointed them out and showed me how they worked.

Like the menu on my cell phone, by pressing the program button, I could scroll through lots of options, including resetting the oil life. Yes, we were back to 100%. But I also noticed that I could view “miles to empty,” and mpg or miles per gallon. That is, as I was driving, if I scrolled to mpg, I could see how my speed affected the miles per gallon I was getting.

You know how you always hear that driving the speed limit–the old-fashioned one at 55 mph–allows you to get the best gas mileage? Well, whoever floated this theory around wasn’t lying. Check out this chart on FuelEconomy.gov that shows just how that works.

I did a little experiment the other day, after discovering this mpg option. I scrolled to it, and left it on as I drove to the highway. I spent 15 minutes driving on a stop-and-go road, and my gas mileage varied between 16 and 18 mpg. Once I hit I-95 and set my cruise control on 55 mph, my mpg shot up to 22 mpg. Interestingly, if slowed down to 50 mph, the mpg went up even more, to 24 mpg, but you’ve got to be nuts to drive that slowly on an interstate.

Now that gas is for sure above $4 per gallon, you can bet that when I have to drive on the highway, I will be setting my cruise control at 55 mpg. Being a competitive person, I hate it when other cars pass me, or I notice that a line of cars is forming behind me–I want to get away and get out in front. However, I’ll just head over to the right lane and live with the fact that though driving 55 mph may add 10 minutes or so to my trip, it will also allow me to fill up less often.