What Effects Fuel Economy on Newer Cars?

Better fuel economy on newer cars.

As cars have evolved they have become much more fuel efficient, but they are also influenced by many more outside factors. With this in mind how does one maintain an automobile so it will deliver its best fuel economy?

The answer to that question is, keep the basics under control! Start with the most basic item, tire pressure. To check tire pressure the tires must be cold. For tires to be considered cold the car could not be driven more than three miles in the last eight hours. Cold tires are the most important part of checking pressure. As you drive friction causes the tires to heat up resulting in a corresponding increase in tire pressure as there is no rating for hot tire pressure the check must be done when the tires are cold. For accurate pressure readings, a quality gauge is necessary; one of Consumer Reports top rated tire gauges is your best bet.

It’s important to know, proper tire pressure is not stamped on the tire. Also, there is no such thing as a generic tire pressure. To get it right, look at your owner’s manual. Your manual will tell you where to look for the decal that shows proper tire size, inflation information and load ratings.

Another system affecting gas mileage is wheel alignment. Improper alignment can decrease fuel economy by as much as 5 miles per gallon. Note: wheel alignment applies to the rear wheels as well as the front so have both rear and front checked.

Oxygenated fuel can decrease fuel economy by as much as 1 mile per gallon. This applies to cars that normally deliver 25-30 miles per gallon on 100% gasoline (NON-OXYGENATED). Higher mileage cars may experience a greater decrease and more thirsty cars may decrease less. Using higher than recommended octane gasoline will not improve fuel economy.

Routinely driving on rough roads will decrease fuel economy. Gravel, dirt, badly rutted roads with rough surfaces, or potholes cause gas mileage to drop. Sometimes significantly!

Tire type and profile can have a big effect on fuel usage. When buying new tires be wary of the salesperson who recommends a different tire profile. You may encounter a salesperson who will say a high performance tire is better than a standard profile tire. This may be true from the standpoint of handling (you will be able to go around corners faster) but you will almost always use more gas, because lower wider tires offer more resistance to rolling. Changing from a 75 series tire to a 60 series low profile high performance tire can cost up to 3 miles per gallon of gas. Higher profile tires may create confusion about gas mileage because they turn fewer revolutions per mile resulting in an odometer error. What appears to be a decrease in mileage may in reality be a slight improvement. For best gas mileage, safety, and overall performance I recommend you buy tires that match all original specifications.

The use of air conditioning will cause a decrease in gas mileage but this may be the lesser of the evils. When you turn the a/c off and roll down the windows you will probably double your economy loss. This is because lowering a car’s windows changes its aerodynamics. Modern cars are designed to move freely through the air. When you open a window the car no longer moves as freely causing the engine to work harder and consume more fuel. These same factors explain why add-on roof racks, luggage strapped to the roof or an open trunk lid will also cost you mileage.

Not using overdrive at highway speeds may decrease your mileage by 3 to 5 miles per gallon. If you are the type person who rides with your foot resting lightly on the brake pedal you will definitely pay. This horrible habit may cause as much as 7 miles per gallon lower mileage than proper driving. Riding the brake pedal results in the brakes being very lightly applied. You may not feel this but it does cause the engine to work harder. In addition to the extra strain placed on the engine a lightly applied brake may disengage the transmission torque converter clutch which further reduces mileage. It also causes lots of expensive wear to the brakes.

For those of you who add electrical gadgets to your car expect to lose 4/10 mile per gallon for each ten amps of electrical energy consumed. Add a set of fog lamps and a radio that each consume 10 amps and expect to lose nearly one mile per gallon.

That toolbox and those bags of sand in the trunk will cost you to the tune of 3/10 mile per gallon for every 125 pounds of added weight. For good gas mileage tighten your load as much as possible.

Always perform all maintenance as required in your owner’s manual. A properly maintained car will give better fuel economy for a longer time. Remember also whenever you experience a noticeable sudden decrease in fuel economy the first thing to check is the engine cooling system thermostat. Today’s cars are equipped with onboard computers that rely on the temperature of the coolant to determine how much fuel should be delivered to the engine. A stuck thermostat can cause the engine to run much colder than normal resulting in up to 8 miles per gallon less fuel mileage.

Last but not least if you love the feel of raw power during acceleration and spend lots of time with your right foot on the floorboard expect a fuel economy penalty up to 15 miles per gallon. This holds true for highway driving also as higher speed automatically means lower gas mileage. Consider this, it takes 15% more fuel to drive 65 mph than to drive 55 mph. The difference gets worse as the speed increases.


Copyright 04/1994 Pat Goss all rights reserved


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