13 Causes For Poor Gas Mileage and How To Restore It

Saving money at the gas pump and maintaining optimal vehicle performance are common goals for many of us. Achieving good fuel economy is directly linked to these objectives. If you find that your car’s gas mileage or fuel economy is poor, there can be various reasons behind it. It could be due to the failure of mechanical parts or harsh driving. This article explains the causes of bad gas mileage and how to recover it.

Taking steps to address issues causing poor gas mileage can ultimately lead to long-term cost savings. Poor fuel mileage can quickly drain your wallet, so it’s important to take prompt action if you notice that your gas gauge is depleting rapidly.

Causes of Bad Gas Mileage

There are different reasons for bad or poor gas mileage, and some of them are given below:

• Clogged Air Filter
• Faulty O2 Sensor
• Faulty Spark Plugs
• Clogged Fuel Injector
• Low Tire Pressure
• Bad Wheel Alignment
• Wrong Octane Fuel
• Cold Weather
• Driving with a Lead Foot
• Carbon Buildup
• Worn Piston Rings
• Faulty MAF Sensor
• Excessive Idling

1) Clogged Air Filter

A clogged or damaged air filter is one of the major causes of poor gas mileage. Replacing the engine air filter is an important routine maintenance job.

It is typically recommended to replace your vehicle’s filters at specified service intervals. If you can’t recall the last time it was changed, it’s crucial to address it promptly.

The replacement cost of an air filter is minimal, so you shouldn’t make any delay to change it. However, driving with a faulty air filter could be costing you more money than the cost of replacement. By allowing the engine to breathe better with a clean air filter, you can improve fuel economy effortlessly.

2) Faulty O2 Sensor

When the Check Engine Light illuminates and indicates a faulty oxygen sensor, it is advisable to replace it without delay. Even though your vehicle may continue to run normally or exhibit minor drivability problems with a faulty sensor, it’s important not to ignore the problem.

A faulty sensor may cause additional fuel to be delivered into the system, resulting in fuel wastage. Moreover, it can elevate CO levels in the exhaust, posing harm to the atmosphere. Swiftly replacing the O2 sensor can help optimize fuel efficiency and minimize environmental impact.

3) Faulty Spark Plugs

The ignition system, including the spark plugs, plays a crucial role in the combustion process of the air-fuel mixture.

If any component of the ignition system, such as an ignition coil, plug wires, or spark plug, malfunctions, it can result in improper combustion of fuel in the affected cylinder. This can lead to poor gas mileage as the unburned fuel goes to waste. Additionally, these problems may cause rough engine idling, stumbling, and hesitation.

4) Clogged Fuel Injector

A dirty fuel injector is one of the major reasons for poor fuel economy. Fuel injectors are responsible for injecting fuel into each engine cylinder in a precise pattern to ensure proper mixing with air.

When fuel injectors become dirty, they may inject fuel poorly, similar to a poorly pressurized shower head. This may significantly reduce engine performance and result in poor fuel economy.

If your fuel injector is clogged, you can clean it, but if internal damage leads to an improper spray pattern, the injector may need to be replaced.

Read More: Clogged Fuel Injector Symptoms and Causes

5) Low Tire Pressure

Maintaining precise air pressure in the vehicle tires is crucial for optimal fuel economy. Whether your tires are overinflated, underinflated, or each tire has various pressure, it may lead to a decrease in fuel efficiency.

To determine the best suitable air pressure for your tires, refer to the panel located inside the driver’s side door. It is important not to rely on the “max pressure” indicated on the tires themselves.

Read More: Low Tire Pressure Symptoms and Causes

6) Bad Wheel Alignment

When your vehicle encounters a hole, you may observe that it requires more effort to drive. This additional energy required translates to increased fuel consumption.

Not only will you end up spending more at the fuel pump, but driving the vehicle will also become physically demanding as you constantly work to steer it back onto the road. Instead of enduring this inconvenience, it is advisable to have your car realigned at the first sign of trouble to restore its proper handling and avoid unnecessary fuel consumption.

Read More: Signs Of Bad Wheel Alignment

7) Wrong Octane Fuel

The octane rating indicates the ability of your fuel to resist combustion under pressure. A higher octane rating signifies greater resistance.

In certain vehicles, you have the option to use premium, mid-grade, or regular octane fuel.

Regular fuel typically has an octane rating of around 87, mid-grade is around 89, and the premium has an octane rating within the range of 91 to 93. For high-end or sports vehicles, it is often recommended to use premium octane fuel.

Opting for a lower octane rating can result in the engine control unit (ECU) adjusting the ignition timing by pulling timing. This means that the spark plug ignites the fuel mixture later during the compression stroke than usual, closer to the top dead center (TDC). Switching back to premium fuel can rectify this issue.

8) Cold Weather

During colder temperatures, your vehicle requires additional time to reach its normal operating temperature. The colder weather causes the oil to become more viscous, which can reduce efficiency, particularly noticeable during short trips.

To maintain the appropriate air-fuel ratio, the car needs more fuel to compensate for the denser cold air. Additionally, gasoline additives used in winter formulas differ from those used in summer. Winter formulas generally contain less energy per gallon.

Unfortunately, there are limited solutions to address this issue. Options include keeping the car in a garage to maintain a warmer temperature or considering relocating to a warmer region for the winter season.

9) Driving with a Lead Foot

Indulging in the thrill of pushing hard on the accelerator and experiencing the power of your vehicle’s engine is undoubtedly exhilarating. However, it’s important to note that this driving style has a significant negative impact on fuel economy.

When you press the accelerator, the throttle opens up, allowing more air to enter the combustion chamber. In response, the engine control unit (ECU) increases the amount of fuel injected to maintain the proper air-to-fuel ratio. The more air you force into the chamber, the more fuel is required to maintain the balance.

If your vehicle has a turbocharged engine, it naturally runs rich, meaning it already has a higher fuel-to-air ratio. By adding even more air through aggressive acceleration, the fuel economy plummets even further. While you don’t have to drive like a grandmother, adopting a more moderate driving style can help you save money by improving fuel efficiency.

10) Carbon Buildup

As your vehicle ages, carbon accumulation becomes a common issue affecting various engine components such as injectors, cylinder walls, pistons, and valves. While a certain amount of carbon buildup is normal, excessive buildup can lead to serious problems.

When carbon buildup affects the valves, it can hinder their ability to seat properly, resulting in reduced compression and negatively impacting gas mileage. This issue is more prevalent in direct injection systems where fuel is directly injected into the cylinder.

In contrast, port injection configurations inject fuel before the intake valve, utilizing the solvent properties of fuel to wash the valves and minimize carbon buildup.

Fortunately, there are several high-end products available in the market designed to clean out carbon deposits and restore optimal performance to your engine. These products can effectively address the issue of carbon buildup and help improve fuel efficiency.

11) Worn Piston Rings

Worn-out piston rings in your engine cylinders can compromise the seal against the cylinder walls, resulting in a loss of compression. This leads to decreased fuel efficiency as the engine loses pressure.

Regular oil changes with the recommended oil type mentioned in your vehicle’s owner’s manual are essential for maintaining the performance of piston rings. Engine oil not only lubricates the rings but also contributes to fuel efficiency.

12) Faulty MAF Sensor

A bad MAF sensor is also one of the major reasons of the poor fuel economy. The MAF sensor of your vehicle plays a crucial role in measuring the amount of air entering the engine. It sends data to the onboard computer to calculate the proper air-to-fuel ratio, which influences fuel injection adjustments.

However, a dirty airflow sensor can cause the computer to inaccurately calculate the air-fuel mixture, resulting in reduced fuel efficiency or even engine stalling. It is recommended to clean a MAF sensor using specialized cleaning sprays.

Read More: Bad MAF Sensor Symptoms and Causes

13) Excessive Idling

When your car is parked, it is unnecessary to let the engine idle for an extended period. Most cars do not require more than 30 seconds to warm up in the morning.

If you find yourself sitting in your car with the engine running while parked or waiting to pick someone up, it’s simply wasting fuel. It is advisable to turn off the engine or put the car in neutral unless it is absolutely necessary to keep the engine running.

How to Restore Fuel Economy?

To restore fuel economy, follow the below-given steps:

1) Use Premium Gas

Certain cars require the use of premium gasoline, and using a lower grade can negatively impact fuel efficiency, resulting in poor gas mileage and undermining your attempts to save money.

2) Avoid Rush Hour

Flexibility in your working hours can offer numerous benefits, including the ability to avoid rush hour traffic. Rush hour not only causes stress and wastes time but also results in increased fuel consumption.

3) Change the Air Filter

Remember to change your air filter whenever you change your oil. A clogged air filter can significantly affect gas mileage as it restricts the engine’s ability to breathe properly. Ensuring a clean air filter is like giving your engine a refreshing decongestant.

4) Add Fuel System Cleaner

If you suspect junk or debris in your fuel lines, you can purchase a bottle of fuel system cleaner for a reasonable price.

Add the cleaner to your gas tank, fill it halfway, and then take a drive on the highway to help the cleaner work its magic.

5) Check Tire Pressure

Regularly check the tire pressure in each of your tires and inflate them if necessary. Additionally, if you have warped wheels due to an accident, it is advisable to seek the assistance of a professional collision repair company to address the issue.

6) Change the Fuel Filter

The fuel filter is an affordable component that, if not replaced, can lead to various issues. When you have your oil changed, you can ask the shop to also change the fuel filter for you, as they will typically accommodate such requests.

7) Change the Spark Plugs and Wires

If you experience significantly poor gas mileage, a possible cause could be faulty spark plugs or wires. It is recommended to have a professional inspect and potentially replace them to ensure optimal performance.

8) Swap the Ignition Coils

In cases where your car exhibits bucking, vibration, and reduced fuel efficiency, it is advisable to have your ignition coils checked by a professional. Addressing any issues with the ignition coils promptly is important.

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