Improving Your Vehicle's Fuel Economy: Is It Possible?

The fuel economy of an automobile is a rating of how far a vehicle can travel on a specific amount of fuel. The less fuel the vehicle uses, the higher the fuel economy. Fuel economy is measured in miles per gallon or miles per gallon gasoline equivalent (MPGe) for electric vehicles. The higher the mpg, the better the fuel economy. Fuel economy is influenced by factors such as driving habits, vehicle weight, tyre pressure, engine health, and weather conditions.

The impact of weather on fuel economy

Weather conditions can have a significant impact on the fuel economy of your vehicle. Here are some ways in which weather influences fuel efficiency:

Cold Weather

Cold weather and winter driving conditions can reduce fuel economy. In city driving, a conventional gasoline car's mileage is approximately 15% lower at 20°F compared to 77°F. This reduction can be even more pronounced for short trips, with a potential drop of up to 24%. The impact is also greater for hybrid vehicles, which can experience a 30-34% decrease in fuel economy. Electric vehicles (EVs) are also affected, with a potential drop of about 39% in mixed city and highway driving.

There are several reasons why cold weather reduces fuel economy:

• Engine and transmission friction increase due to cold engine oil and other fluids.
• Engines take longer to reach their most fuel-efficient temperature, affecting shorter trips more significantly.
• Additional power is used for heated seats, window defrosters, and heater fans.
• Warming up the vehicle before starting a trip lowers fuel economy, as idling gets 0 miles per gallon.
• Colder, denser air increases aerodynamic drag, particularly at highway speeds.
• Tire pressure decreases in colder temperatures, leading to increased rolling resistance.
• Winter-grade gasoline may have a slightly lower energy content per gallon than summer blends.
• Battery performance decreases, impacting the regenerative braking system in hybrids and EVs.
• Icy or snow-covered roads reduce tire grip, wasting energy.
• Safe driving speeds on slick roads are typically lower, further reducing fuel economy, especially below 30-40 mph.
• Using four-wheel drive increases fuel consumption.

Hot Weather

While cold weather can negatively affect fuel economy, extremely hot temperatures can also have an impact:

• The engine cooling fan operates more frequently, consuming additional power.
• Increased engine idle time is used to keep the cabin cool, which can affect fuel efficiency.

Rain, Snow, and Wind

Adverse weather conditions such as rain, snow, or slush can also influence fuel economy:

• Precipitation on the road increases rolling resistance as tires have to push through the water or snow, and the tires, transmission oil, and axle oils are cooled, reducing their efficiency.
• Headwinds and crosswinds increase aerodynamic drag, reducing fuel efficiency. For every 10 mph of headwind or crosswind, fuel efficiency can decrease by up to 13%.
• Winter blend fuels, which are used during colder months, may contain additives that adversely affect fuel efficiency.

In summary, weather conditions can significantly impact the fuel economy of your vehicle. Cold temperatures, hot weather, rain, snow, and wind can all contribute to reduced fuel efficiency. Understanding these factors can help drivers make informed choices to optimize their vehicle's performance and fuel consumption.

How to improve fuel economy through driving habits

Driving habits can significantly impact fuel economy, and making some simple changes can help improve efficiency, conserve fuel, save money, and reduce emissions. Here are some tips to improve fuel economy through driving habits:

Avoid Aggressive Driving

Aggressive driving behaviours, such as speeding, rapid acceleration, and hard braking, can negatively affect fuel economy. Analysis by the Massachusetts Institute of Technology shows that aggressive driving can lower fuel economy by 15-30% at highway speeds and 10-40% in stop-and-go traffic. Instead, drive smoothly and avoid fast acceleration and sharp braking. Maintaining a steady speed and acceleration will help improve fuel efficiency.

Reduce Short Trips

Short trips, especially when the engine is cold, can use up to 20% more fuel. This is because a cold engine is less efficient and requires more fuel to warm up and operate optimally. If possible, combine multiple errands into one trip or consider alternative modes of transportation for shorter distances.

Maintain Optimal Speed

Driving at extremely high or low speeds can impact fuel economy. When cruising on a highway, the engine works harder to overcome wind resistance, increasing fuel consumption. On the other hand, driving too slowly can cause the engine to drop to a lower gear, also using more fuel. Maintaining a steady speed within the optimal range, typically between 50-90 km/h, can help achieve better fuel efficiency.

Reduce Unnecessary Loads

The weight of your vehicle affects fuel consumption. Every extra 50 kg increases fuel consumption by 2%. Remove unnecessary items from your car, especially heavy ones, to improve fuel efficiency. Additionally, consider removing roof racks or spoilers that increase air resistance and fuel consumption.

Maintain Proper Tyre Inflation

Underinflated tyres have higher rolling resistance, generating more friction and increasing fuel consumption. Ensure your tyres are properly inflated to the recommended pressure. This can improve fuel economy and also enhance tyre longevity and safety.

Use Air Conditioning Wisely

Using the air conditioning can increase fuel consumption. However, at speeds above 80 km/h, driving with the windows down causes more wind resistance and uses more fuel. In such cases, using the air conditioning may be more fuel-efficient. Additionally, removing sludge and corrosion between engine parts through regular servicing can also help improve fuel efficiency.

The role of vehicle design and maintenance

Vehicle Maintenance:

• Engine Maintenance: Regular engine maintenance is vital for improving fuel economy. This includes routine checks, oil changes, air filter replacements, and spark plug inspections. For example, using the recommended grade of oil can increase mileage by up to 2%.
• Tire Inflation: Keeping tires properly inflated can improve fuel mileage by reducing rolling resistance. Under-inflated tires can lower gas mileage, and it is estimated that for every 10 psi drop in tire pressure, there is a 1% loss in fuel economy.
• Air Filters: Replacing clogged air filters ensures optimal airflow to the engine, improving combustion efficiency. A clogged air filter can cause the engine to consume more fuel, while a clean air filter can improve mileage by up to 10%.
• Spark Plugs: Worn-out spark plugs can lead to incomplete combustion, wasting fuel. Regularly replacing spark plugs ensures efficient ignition, maximising fuel economy. Well-maintained spark plugs can improve mileage by up to 30%.
• Engine Issues: Addressing engine issues promptly, such as a loose gas cap or check engine light, can help maintain fuel economy and reduce emissions.

Vehicle Design:

• Aerodynamic Devices: Damaged aerodynamic components, such as torn chassis skirts, can negatively impact fuel economy. It is important to repair or replace these parts to maintain optimal fuel efficiency.
• Tires: The design and condition of tires play a significant role in fuel economy. Low-rolling resistance tires can improve fuel efficiency by reducing friction and resistance.
• Engine Oil: Using the right type of engine oil can boost fuel economy by reducing friction between moving parts. Oil analysis is essential to ensure the oil maintains the correct viscosity and performance.
• Wheel Alignment: Proper wheel alignment reduces tire rolling resistance, which improves fuel economy. Misaligned wheels increase drag, causing the engine to work harder.
• Air System: A clogged air filter in an electronically controlled engine can affect the fuel-air mix, leading to increased fuel injection and impacting fuel economy.
• Other Systems: Issues with the cooling system, electrical system, HVAC, and idle reduction technologies can also contribute to reduced fuel economy, even if the impact is small.

By focusing on proper vehicle maintenance and design, drivers can optimise their fuel efficiency, reduce fuel consumption, and lower their environmental impact. These strategies not only save costs but also contribute to a cleaner, more sustainable future.

The difference between fuel economy and fuel efficiency

Fuel economy and fuel efficiency are two terms that are often used interchangeably, but they have distinct meanings. Fuel economy refers specifically to the distance travelled by a vehicle per unit volume of fuel consumed. This is typically expressed in terms of miles per gallon (mpg) or kilometres per litre (km/L). On the other hand, fuel efficiency is a broader, more descriptive term that refers to how efficiently a vehicle uses fuel. It is a form of thermal efficiency, which is the ratio of effort to the result of a process that converts the chemical potential energy in fuel into kinetic energy or work.

Fuel economy is a well-defined measure that is commonly used in the automobile industry and is familiar to anyone who has purchased a car, especially in the US. However, fuel efficiency, as a more general concept, can be applied to various devices and applications beyond transportation, such as fossil fuel power plants or industries dealing with combustion.

While fuel economy focuses on the distance travelled per unit of fuel, fuel efficiency considers the overall efficiency of the vehicle in utilising fuel. This includes factors such as engine efficiency, transmission design, tyre design, aerodynamic drag, weight, and driving habits. Improvements in these areas can lead to better fuel efficiency and reduced fuel consumption.

It is important to note that while the terms are related, they can provide different perspectives on fuel usage. For example, John Heywood, Professor of Mechanical Engineering, suggests that thinking in terms of fuel consumption, measured in gallons per mile, can be more informative than miles per gallon. This is because gallons per mile "tells [you] exactly how many gallons of gas [you] use if [you] drive 100 miles". This perspective highlights the actual amount of fuel consumed and can help in understanding the impact of improvements in fuel efficiency.

In summary, while fuel economy and fuel efficiency are interconnected concepts, they represent different ways of evaluating fuel usage in vehicles. Fuel economy focuses on the distance travelled per unit of fuel, while fuel efficiency considers the broader efficiency of fuel utilisation, including various vehicle design and performance factors.

How to calculate fuel economy

Fuel economy in automobiles is the distance travelled by a vehicle in relation to the amount of fuel consumed. This can be expressed in terms of the volume of fuel used to travel a certain distance, or the distance travelled per unit volume of fuel consumed.

The fuel efficiency of motor vehicles can be expressed in multiple ways:

• Fuel consumption is the amount of fuel used per unit distance; for example, litres per 100 kilometres (L/100 km). The lower the value, the more economical the vehicle is.
• Fuel economy is the distance travelled per unit volume of fuel used; for example, kilometres per litre (km/L) or miles per gallon (MPG). The higher the value, the more economical the vehicle is.

Calculating Fuel Efficiency

Fuel efficiency can be reported in litres per 100km or kilometres per litre (and similarly using miles and gallons).

Litres per 100km fuel economy calculator:

• Divide the litres it took to refill the tank by the distance travelled and multiply by 100.
• For example, 60 litres / 800km * 100 = 7.5 litres per 100km (expressed 7.5l/100km).

Kilometres per litre fuel economy calculator:

• Divide the kilometres travelled by the amount of litres it took to refill the tank.
• For example, 800km / 60 litres = 13.3km per litre.

Calculating Fuel Economy for Electric Vehicles

If the vehicle is fully electric (i.e. plug-in EV) then it is best to calculate kilowatt hours per 100km. If you recharge your car at a commercial station, calculate how much it costs between fills.

Calculating Miles per Gallon (MPG)

• Fill up your gas tank all the way.
• If your car has a trip odometer, reset it, or record the master odometer mileage.
• Drive your car as you normally would, and let your gas tank deplete to at least half a tank of gas.
• Fill your tank again and record the amount of gas it took to refill.
• Record the elapsed trip miles or new odometer mileage.
• Get the miles travelled from the trip odometer, or subtract the original odometer reading from the new one.
• Divide the miles travelled by the amount of gallons it took to refill the tank. The result will be your car’s average miles per gallon yield for that driving period.

Calculating Your Rate of Gas

• Take the average price you pay at the pumps per gallon and divide that by the number you found when you calculated mpg for your car.
• For example, price per gallon / miles per gallon = price per mile.

Tips to Improve Fuel Efficiency

• Keep your tyres pumped up. Underinflated tyres have higher rolling resistance, increasing fuel consumption.
• Lose the weight in your boot. Every extra 50kg increases fuel consumption by 2%.
• Avoid driving with the windows down at speeds faster than 80km/h. Contrary to what you may think, it's more fuel-efficient to drive with the air conditioning on.
• Maintain a steady speed of 50-90km/h on the highway. Driving too slowly or too fast increases fuel consumption.
• Avoid aggressive acceleration and braking.
• Plan your route to avoid rush hour traffic.
• Turn off your engine if you're waiting for more than three minutes.
• Regularly service your car.

Frequently asked questions