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15 Causes of Poor Gas Mileage Every Car Owner Must Know


Poor gas mileage means that your vehicle is not running and operating effectively and efficiently, specifically when it comes to fuel consumption. This also means that you are required to refuel your car more often. But, what are the main causes of poor gas mileage?

Top 15 Causes of Poor Gas Mileage & Fuel Economy

Causes of Poor Gas Mileage

Al thought colder temperatures is one of the main reasons why your vehicle can be experiencing poor MPG or miles per gallon; there are some other common reasons that can be causing bad fuel economy as well:

1. Dirty Fuel injectors

You will notice a significant drop in fuel efficiency if you have a clogged fuel injector. The building up of fuel varnish deposits inside the injectors hinders the injectors from performing their usual work of putting fuel into the car engine. This automatically results in lean misfires due to fuel as well as lean air mixture.

In case the injectors leak fuel, it is given that less fuel will reach the engine making the engine to run less efficiently and waste more fuel. To solve this, you need to add a bottle of good and quality fuel injections into your tank of fuel. You should note that this may take some time before you notice any improvement.

2. Bad Oxygen Sensors

Lacking good and quality oxygen sensors and air filters reduces the level of gas mileage in your vehicle since the sensors for oxygen help in keeping the proper air and fuel mixture. The off-balance of fuel and air results in inefficiencies.

3. Clogged Air Filters

When the air filters are clogged, they cause poor gas mileage. To fix this problem, they need to be unclogged. It is good to note that for the engine to work at its peak performance, you need to clean the air filters thoroughly and, at times, replace them.

Some of the benefits of changing/replacing the engine air filter include reduced emissions since clogged air filters reduce the flow of air to the engine. Also, it increases the efficiency of the fuel and prolongs the life of your car engine.

New filters trap debris and dirt that can damage the internal parts of the engine, especially the pistons and the cylinders. Also, new air filters can increase gas mileage and improve the performance of the engine due to the optimal flow of air.

4. Poorly/non-functioning Spark Plugs or Wires

Ignition coils spark plugs are the ones that cause sparking combustion in your car engine. In case they are poorly working, or they misfire, they negatively affect the gas mileage. Regular check-ups, as well as changing of spark plugs, should be done to enhance gas mileage.

5. Poor and Aggressive Driving Habits

Aggressive drivers always accelerate very quickly instead of moderately. This results in more consumption of fuel and, in turn, results in using more gas than you require. This same case applies when you are revving your car engine. You should avoid quick accelerating so as to economize your car fuel consumption.

6. Excessive Idling

Having your engine on and you are not moving or parking your car, or also called idling. Mostly this happens when drivers are waiting to pick someone or are trying to warm their cars during cold weather.

Note that your car engine requires few warming seconds. It is recommended that you turn off your car engine or put it in a neutral mode while waiting for somebody. This obviously minimizes the fuel used and help in conserving the environment.

7. Obstructions In The Exhaust System

Obstructions may be as a result of the crimped or crushed exhaust pipe or internal problems of the exhaust, which include a muffler that has collapsed or clogged converter. This creates pressure that leads to increased use of fuel. In this case exhaust system should be fixed.

8. Use of The Wrong Kind of Oil Viscosity or Motor Oil

Poor gas mileage is also a result of the kind of oil used in a given vehicle. Oils that are very low when it comes to reducing friction result in gas mileage problems. You should also know that oil, which has heavier viscosity, will increase the consumption of gas.

Your car requires motor oils that reduce friction greatly. Some of these fuels include synthetic oils and oils recommended by the car’s manual. Avoid buying a thicker oil at all costs. For this, you can refer to the owners manual.

9. Excessive Use of Your Air Conditioner

Running your air conditioner while driving is another common cause. This causes wastage of a lot of gas as your car powers this system. It is good to turn off your air conditioner by riding while your car windows are open so as to increase the gas mileage. To reduce drag, you should close the windows at high speed.

10. Cooling System Problems

Overheating of your car engine due to cooling system problems: a car engine that runs hot after a number of revolution increase gas consumption leading to poor gas mileage. Heat also reduces the efficiency of the engine over a period of time. In case there is a deficiency of air in your car’s cooling system, you should check the thermostat and fix it to solve this problem and to ensure that the engine gets up to temperature efficiently and quickly.

11. Having a Heavy Foot On The Pedal

The number of revolutions made per minute plays an important role. The higher the engine revolution, the higher the consumption of fuel. In order to solve this, you need to drive slower than usual with a recommended speed of fifty-five (55) miles per hour.

Stepping your foot hard onto the pedal can get your combustion chamber heavily mixed with air. When this happens, the ECU or engine control unit will infuse more fuel to keep up the appropriate air-fuel proportion. This action will cause your gas mileage performance to go down.

12. Low Tire Pressures & Bad Wheel Alignment

According to Fueleconomy.gov, for every 1 PSI drop in your tires, it can be costing you a 0.2% increase in gas consumption. So YES, keeping your car tires with the correct amount of pressure does wastes gas.

A car that has bad wheel alignment will continuously fight against the resistance of your tires. This, in the long run, will end up reducing fuel efficiency and excess fuel being consumed. Avoid bad gas mileage by getting an alignment as soon as possible.

According to the U.S. Department of Energy, by upgrading to low rolling resistance tires, you can get up to 10% of fuel savings.

13. Choosing a Different Octane Rating

The octane rating describes the ability of a fuel to resist combustion under pressure. The higher the octane rating, the more resistant to knocking. When it comes to adding the proper octane fuel rating to your gas tank, you should always start with the owner’s manual.

The average in regular vehicles will allow the owner to choose between regular (around 87 octanes), mid-grade (around 89 octanes), or premium (91 to 93 octane) gasoline.

Additionally, the lower octane grade used, the less direct injection the ECU will apply. Therefore, the ignition system and timing will get affected directly by your octane rating selection.

14. Overfilling the Engine Oil Level

If you change the oil and end up overfilling it, it is possible that the oil level in the crankcase will be high enough to reach the crankshaft. If this happens, the crankshaft will end up pushing its way through a puddle of oil, which is a wasted effort that you will notice at the fuel pump.

A simple solution to this is to buy a fluid extractor and draw enough oil out of the dipstick hole to bring the level back below the full mark on the dipstick.

15. Carbon Buildup In The Engine & Fuel system

As your vehicle ages, carbon develops in cylinders, valves, and even on the cylinder wall. Some carbon development is totally normal. However, from time to time, an excessive amount of carbon develops in the basic regions.

This can influence the ability of valves to work properly or cylinders to seal. This thus reduces pressure, which decreases productivity and, subsequently, ends with poor fuel economy.

How to Fix Poor Gas Mileage Problems

To get the best fuel mileage, you should do the following:

  • Regular changing of your car oil so as to reduce more friction. This helps you in getting better gas mileage.
  • Since the air conditioner is the worse consumer of gas, turn it off while riding. Use your windows to cool yourself.
  • Always plan before driving. Know the specific routes that will economize your fuel consumption. Remember, the more you stop after braking and accelerate so as to start, automatically leads to faster burning of gas. Use a smooth sailing route.
  • You should avoid idling your engine since you waste your fuel while doing nothing.
  • Changing your style of driving. Don’t accelerate your car when it is not needed, as this reduces the use of gas.
  • If it is possible, ensure that you light the load in your vehicle. This also improves gas mileage, reducing the number of trips that you make to the gas station.
  • Inflate your car tires properly. Inflating them, we’ll help in increasing the economy of fuel use besides making your tires look good.
  • Embrace regular maintenance. This will help you in detecting factors affecting your gas mileage and finding a solution to those factors, which may include malfunctioning oxygen sensors, worn piston rings, bad fuel injector, or air filters.


Most of the previous causes of bad gas performance can be treated with preventative maintenance. Taking your vehicle to get regular oil changes does not only work to prevent an engine issue. Vehicle maintenance can also help you avoid the main reasons for poor gas mileage.

Another known cause for older vehicles is the incorrect timing of engines. Typically, this problem will be discovered after the check engine light on your car will come up. It is an issue that will boost your fuel costs in the long run.

Last Updated on: February 21, 2024

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