Q: My automatic vehicle has a button on the shifter that says “O/D.” I usually leave it pushed in, or on, and when I press it off, my dashboard light says “O/D Off.” What does O/D mean, and what does this function mean for my vehicle?
A: “O/D” means over drive. The simple answer is that the over drive function gives vehicles a better fuel economy when driving at high speeds on the highway. Technically, the function gives your vehicle a higher gear ratio, allowing the car to move faster at a lower RPM (revolutions per minute). The higher the engine’s gear ratio, the more torque it’s capable of producing.
Q: Does low tire pressure really effect gas mileage?
Yes. The area of tire that touches the ground at any given moment is the “contact patch.” A tire with low tire pressure will have a large contact patch (picture a flat tire). All of that contact with the ground creates friction (drag) that the vehicle must overcome in order to move forward. Thus the car uses more fuel.
Tire pressures can vary, based on the make/model of your vehicle, outside temp and your tires. It’s important to note that the PSI on the wall of your tire is a maximum recommendation. Always check your owner’s manual if you are unsure of the correct PSI, and remember to check the pressure in your tires about once a month.
Q: How often should I change my oil?
This is a hard question to answer for a variety of reasons. Every vehicle is different, and require different needs. The answer also depends on how much driving you do, and what kind of oil you use. Finally, no one has a better answer than your owner’s manual; so when in doubt, check it out.
With that said, here is the simple answer: synthetic oil should be changed every five to seven thousand miles (less often), while conventional oil should be changed every three to five (more often, or every three months). Motor oil lubricates and regulates the temperature of the moving parts inside your engine. Newer vehicles burn oil at a lower rate, due in part to government regulations and changes in vehicle building materials (i.e., more plastic parts versus a traditional metal). Most cars will tell you (via the oil light on your dash) when they need new oil. For those who go longer stretches between changes, just remember to check your oil levels on a regular basis.
About Our Tech
Norm Michaud, a Master Guild Audi technician, was the contributing expert for this post. Michaud has worked in the automotive industry since 2002; prior to that he worked in aeronautics and mechanical design. Michaud has spent his entire automotive career working with Audis, coming to Hoffman Audi of East Hartford . Though he drives a Ford at the moment, if he could drive any Audi it’d be a Q5.