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What Causes High Fuel Consumption?

I am a fully licensed automotive technician who has worked on all makes.

What creates poor fuel economy? The fuel consumption you achieve with your vehicle may differ from published ratings, depending on how, where and when you drive and the optional equipment you have installed.

Many Factors Affect Fuel Consumption

  • Your driving style and behaviour
  • Vehicle acceleration (best to have steady acceleration to prevent tire slippage)
  • Braking and driving speed
  • Overall age and condition of your vehicle
  • Temperature (affects the time to warm the vehicle up to operating temperature)
  • Weather (for example snow or rain)
  • Traffic
  • Road conditions (paved roads, unpaved roads, off-roading)
  • Drive systems (i.e., 4-cylinder or V6 engine, automatic or manual transmission, 4-speed or 5-speed transmission, CVT)
  • Powered accessories (air conditioning, radio, dvd players)
  • Break-in of a new vehicle. New vehicles should accumulate some mileage before fuel consumption is tested.
  • Cold weather. Canadian winter conditions, for example, will always have a negative impact on fuel economy. Fuel consumption judgements should be made during warmer seasons (i.e., 20° Celsius)
  • Proper tires and tire inflation. Under-inflation and improper tires create more friction.
  • Fuel quality
  • Cargo load and trailer towing
  • Engine management issues. If an engine malfunction is hurting fuel efficiency, modern on-board diagnostics should trip a diagnostic trouble code (and turn on the Check Engine light).

Proper Vehicle Maintenance Saves Fuel

Engine oil. Oil removes dirt, metal shavings and other impurities from the engine and captures them in the oil filter, while lubricating the moving parts of the engine, which promotes better fuel efficiency. You can pay a severe penalty for neglecting engine oil, possibly even needing to replace the engine itself.

Cooling system. The cooling system keeps the engine at its optimal operating temperature. Outside this range, fuel consumption increases. Coolant degrades over time, and it’s important to change it as specified by the manufacturer.

Ignition system. If one or more of the spark plugs or wires are worn or malfunctioning, the engine will misfire, and some fuel will remain unburned, which wastes fuel, produces higher levels of emissions and generally performs poorly.

Air filter. A dirty air filter reduces performance and increases fuel consumption. Replace the air filter according to the recommendations during routine check-ups.

Tires and wheel alignment. Rolling resistance results in premature tread wear when your tires are under-inflated or misaligned, and increases fuel consumption. Measure tire pressure (when tires are cold) at least once a month. Also check your tires for uneven wear. Rotating your tires also helps prolong their life and improve fuel economy. Read this article about choosing the right tires and maintaining them.

Brakes. Dragging brakes (when the brake pad or shoe fails to release from the disc or drum) can significantly increase fuel consumption because the vehicle must work harder to overcome the resistance. It is important to have your brakes inspected at the interval specified in the owner’s manual.

Regular oil changes prevent sludging and engine damage. Use the proper graded of oil for optimum engine performance (minimal friction).

Regular oil changes prevent sludging and engine damage. Use the proper graded of oil for optimum engine performance (minimal friction).

Driving Tips to Improve Fuel Consumption

  • Avoid short trips.
  • Reduce idling.
  • Drive smoothly and efficiently.
  • Drive in the appropriate gear.
  • Slow down.
  • Use cruise control.
  • Lighten your load.
  • Keep your vehicle properly maintained.
  • Keep tires properly inflated.
  • Use power accessories (like air conditioning) wisely.
  • Use a block heater during winter temperatures.

Better Driving Habits Save Fuel

Accelerating. Hard, fast acceleration guzzles gas and wears out your engine and tires quicker. Avoid unnecessary slowdowns or holdups by taking your foot off the accelerator well in advance of the intersection and coasting toward it.

City traffic. A European test showed that “jackrabbit” starts from traffic lights and hard braking reduce travel time by only 4% while increasing fuel consumption by 37%. The more fuel-efficient option is to accelerate smoothly and maintain a steady speed.

Highway driving. It takes energy to get a vehicle up to cruising speed, so accelerate smoothly when passing other cars or when merging with faster traffic and avoid hard braking. With most vehicles, increasing cruising speed from 100 km/h to 120 km/h will increase fuel consumption by about 20%.

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Pedal use. Some motorists drive with their left foot resting on the brake pedal, a habit that increases fuel consumption and wears out the brakes prematurely.

Idling. Idling for more than 60 seconds can use more fuel than turning off the engine and restarting it again. Excessive idling can contaminate engine oil and damage engine components.

Air Conditioning. Minimize your use of air conditioning in the summer to improve your fuel efficiency.

Aerodynamics. The impact of aerodynamic drag is relatively small at low speeds. Ski racks and roof racks increase aerodynamic drag.

Weight. Extra weight in your car means wasted fuel and unnecessary emissions.

Winter driving can be a headache, especially when you are stuck in a traffic like this!

Winter driving can be a headache, especially when you are stuck in a traffic like this!

Driving in Cold Weather and on Hills

Cold weather. An engine can burn up to 50% more fuel for a short trip in the winter than for a the same trip in the summer. In temperatures below 0° Celsius, block heaters can improve overall fuel economy by 10% or more.

Snow and vehicle weight. Snow building up in the wheel wells, under bumpers, and on top of the vehicle adds weight and rubs against the tires, further increasing rolling resistance caused by snow and slush.

Tire inflation. Cold temperatures decrease the air pressure in the tires, adding to the rolling resistance caused by snow and slush.

Tire type. Tires marked with “M + S” (mud and snow) or “all season” tires that do not have the peaked mountain-with-snowflake symbol, may provide safe performance in most weather conditions, but are not designed for snow and ice-covered roads. Snow tires will improve traction, reduce tire slippage, improve safety and save fuel. All-season tires do not provide the same grip at temperatures below -15º Celsius. The more your vehicle slips and slides and spins its wheels, the more fuel you can waste.

Hilly terrain. It’s more fuel-efficient to let your speed drop going uphill and build it up again going down the other side.

Subaru XV Crosstrek after one minute of idling and two minutes of driving during the winter season

Subaru XV Crosstrek after one minute of idling and two minutes of driving during the winter season

Don't Worry About a High Fuel Consumption Rate After Two Minutes of Winter Driving

The mileage figure above looks awfully high: 99.9L/100km. But it doesn't necesarily mean there is something wrong with the vehicle or that you are a horrible driver. This is an example of the "average fuel consumption" during winter after two minutes of driving during winter and one minute of idling. It says "99.9L/100km: because during the one minute of idling means the vehicle did not drive any "kilometres" for the "litres" of gas that was used.

The longer you idle, the longer it takes for the "average fuel consumption" meter to "average" back closer to manufacturer specifications. Another simple reason why it will take long a long time to average lower during winter is that during cold weather , it will take a longer time for the vehicle to heat up to the point where all the sensors are in closed loop and operate efficiently.

Subaru XV Crosstrek: after 1 minute of idling, 14 mins and 10 kms of driving during the winter season

Subaru XV Crosstrek: after 1 minute of idling, 14 mins and 10 kms of driving during the winter season

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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