3 Most Likely Causes of Reduced Fuel Mileage

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Have you come to the conclusion that your automobile just isn’t getting the kind of fuel mileage that it did 12, 6, or even 3-months ago? With the thermometer and fuel prices climbing higher and higher, you can’t afford to allow your fuel efficiency to slip even a little bit. Fuel efficiency is not something that should fluctuate regularly and changes in the total number of miles that you can travel on a single tank of fuel should be fervently investigated. In most instances the cause of dwindling fuel mileage can be traced back to improper maintenance. Because time, mileage, and normal wear-and-tear are responsible, the reduction in fuel efficiency can be gradual. Only after fuel consumption has reached an unacceptable level do most motorists begin to calculate a solution. Carefully monitoring fuel mileage consistently is vital to optimum fuel efficiency and adequate stewardship of our natural resources.

Here are the three most likely causes of reduced fuel mileage.


Tires that are under or over inflated can cause your fuel mileage to suffer by as much as 5-percent. Insufficient air pressure in on or more tires can force the engine, transmission, and differential to work harder at maintaining vehicle speed, thus reducing fuel mileage. Under inflation can also harm the tire’s sidewall and tread if the tire is forced
to bear the weight of the heavy vehicle. Over inflation promotes uneven and accelerated tire wear, as well. Over inflated tires tend to wear out prematurely in the center of the tread and have a tendency for belt separation. Underinflated tires promote choppy or uneven tread wear which can cause excessive vehicle vibration that kills fuel mileage. If you experience any type of abnormal noise or vibration from your tires and wheels, please have it checked by a qualified technician, immediately. Maintain the tire’s maximum inflation rate, listed on the sidewall near the bead of the tire/wheel.


Low engine oil levels can place your engine into s strain that robs valuable fuel mileage. Virtually every vehicle will burn at least a quart of oil between services. During this vital period, when your engine is down a quart of oil it can average 10-percent worse fuel efficiency than when the oil has been recently changed. Check your engine oil and other vehicle fluid levels weekly and add fluid as needed. Maintain a service schedule that centers around changing your engine oil and filter, as well as using the proper oil recommended by the manufacturer, and you will save money on fuel.


It is a safe bet to say that you need to perform engine tune-ups at proper increments for optimum fuel mileage. The air filter should be inspected at each oil change, the fuel filter (if serviceable) should be changed every 30,000-miles, see your owner’s manual for service intervals regarding spark plugs, ignition coils or spark plug wires, PCV, distributor cap, and rotor button (if equipped). Keeping tune-up parts changed at regular manufacturer suggested intervals will help to maintain optimum fuel efficiency. Use the right tune-up parts. If your vehicle was equipped with double-platinum spark plugs from the factory, then use double platinum spark plugs throughout the life of the vehicle. The same is true of any type spark plug. Resistor type spark plugs may be on sale for 83-cents but if they will cost you a fortune in fuel and your vehicle will never perform to its full potential are they still a bargain. Always use OEM quality parts or better. I have had more success using Delco spark plugs in GM vehicles, NGK and Nippendenso for Japanese vehicles, Autolite spark plugs in Fords, and so on, than trying to cut corners with cheaper or gimmick spark plugs.

S.M. Darby

S.M. Darby

I am a freelance author with over 25 years of experience as a professional, ASE certified automotive technician and shop owner, muscle car enthusiast, avid street racer, and classic car restoration specialist.