In "Maximizing Fuel Economy Part 1 — Driving Tips," I told you about some simple driving techniques to help improve fuel economy. But as you might imagine, that’s not the whole story. Another area to pay attention to is the overall condition of your car itself. Sometimes the basic maintenance that we take for granted can make a difference in fuel economy, so this time I’ll tell you about that.

Engine Oil Level and Condition

When oil becomes very dirty or the level is low, the oil’s ability to properly lubricate the engine’s moving parts is compromised. That means more friction, and more friction in turn means more drag and wear. Keep your oil level topped off between changes, and use a good quality brand of oil.

If your owner’s manual suggests a range of different oil weights for the engine, then use the lighter-weight oil. 5W-20 oil will have less drag then a 10W-30. But only do so if the manufacturer’s recommendations include that lighter oil. Synthetic oils can also reduce friction and drag, but they also cost more. Synthetics do, however, hold up better for longer durations and in high heat conditions, so keep that in mind too.

By the same token, consider replacing the oils in the transmission, axles and transfer case (if applicable) with appropriate synthetic oils. That will reduce drag in those components, which also promotes an improvement in fuel mileage.

Tire Pressures, Types and Sizes

Keeping your tire pressure in check will improve your fuel economy. The air compressed inside the tire is what carries the weight of the car. If there isn’t enough air pressure, the tire will squash down under the car’s weight. Two things happen: 1) the tire’s contact to the road is widened, increasing the amount of friction created against the road, and 2) the tire’s sides are forced to bend and deform much more then normal. This not only creates more friction and resistance, but it can also do permanent damage to the tire itself. There are two tire pressure ratings on and about your vehicle. One is the maximum safe pressure that the tire can handle. This is molded right on the side of the tire. This is a maximum rating, not a recommended rating. The actual recommended pressure rating is determined by the vehicle manufacturer. It can typically be found on a decal located on one of the door jams, inside the glove box, or inside the fuel filler door. The vehicle design engineers spend a lot of time determining the ideal pressure for that car, so unless you face special conditions (like carrying a heavy load), their recommendation is what you should follow.

Also on this topic, larger aftermarket wheels and wider tires are popular. But understand that a wider tire will have greater rolling resistance. This is good for cornering, bad for fuel economy. I noticed a 2 mpg loss when I put a wider, 15 inch wheel and tire package on my little car in place of the stock 14’s. Using massive, 24-inch wheels may be all the rage these days, but those wheels are heavy. A heavier wheel and tire combination means that you have to accelerate that extra weight every time you leave a traffic light. And that will take its toll on fuel usage. So if you feel inclined to go rollin’ on the ‘dubs, keep in mind that there is a trade-off.

Tune-Up Time

Cars these days are advertised as being able to go long periods of time without a tune-up. But if your car has six-digits showing on the odometer, it might be time to take a look at a few things, starting with your spark plugs and wires. Platinum-tipped plugs last a long time, but they still wear out. Over time, the casings on plug wires can dry rot and crack. This can lead to the occasional stumble and less-then-ideal efficiency. Changing these parts is often (relatively) cheap and easy, so it might be time to just do it. Same goes for your air and fuel filters.

Also, the engine’s oxygen sensor degrades over time. The engine computer uses this sensor to know how much fuel is needed to go with the air being pulled into the engine. If it fails, the computer typically defaults to a fail-safe mode which protects itself by running extra fuel-rich. That means that the economy drops. O2 sensors are often relatively inexpensive and should be considered a normal, preventative maintenance replacement on any older vehicle.

One more thing to think about – the catalytic converter also has a finite lifespan. Over time, these can plug up, which in turn leads to degraded performance and reduced efficiency. This is not as common as an O2 sensor failure, and can sometimes be a bit pricy to replace. But if you do notice a loss in performance, then it is one of the items that should be investigated.