9 Causes of Poor Gas Mileage (Increase Your MPG)

We all strive to get good fuel mileage in whatever vehicle we are driving. The majority of people on the road are driving vehicles powered by either a gasoline or diesel engine. Electric powered vehicles are an entirely different topic.

Although diesel and gasoline engines are different, they also have similarities as well. Some of those similarities pertain to problems that can occur which will cause them to consume too much fuel and make their fuel economy worse.

Most high fuel consumption issues relate to some kind of engine problem, whether the problem is directly associated with the engine or something else in the car that is not allowing the engine to do its job properly. Here are nine of the most common causes of your vehicle using too much fuel.

Top 9 Reasons of Excessive Fuel Consumption

1) Carrying Excess Weight

car roof rack weight

One simple cause of high fuel consumption is when a vehicle is carrying too much weight, whether it has a lot of items in the trunk, full of people, carrying a roof cargo box, or pulling a trailer.

The more weight that’s being carried around by the vehicle, the more demand that is being put on the engine to generate enough power to move all of it. In the case of a roof rack, you will also have additional wind drag to deal with which also affects your MPG.

Whenever the need for more power is needed, whether cruising or accelerating, the engine needs to burn more fuel to make it happen. Therefore, you end up having to fill up your fuel tank more often.

Keep in mind that excess weight resulting in lower gas mileage is often proportional to the amount of power a car produces. For example, an extra 100 pounds in a full size truck won’t be a big deal but that extra weight will have a big impact on your Smart car’s MPG.

2) Bad Spark Plugs

best spark plugs

When spark plugs get worn out, you will have more engine misfires with your vehicle which will use up more fuel. You need to be sure to use the best quality spark plugs possible, so you can get the most miles out of them. Iridium spark plugs and platinum spark plugs are the two most preferred types.

3) Dirty Air Filter

clogged air filter

There are many reasons to have a clean air filter, but one big reason is to have good fuel economy. If your air filter is clogged or dirty, less air makes its way into the combustion chamber making the engine work a lot harder to satisfy the power requirements of the driver.

This may even cause a running rich condition where the air/fuel mixture is not optimal. So, remember to change your air filter at the recommended interval set by the vehicle manufacturer. Your vehicle manual will have this information.

4) Low Tire Pressure

best tire pressure gauge

The tires on your vehicle need to be inflated to the proper amount of air pressure, usually between 32 PSI and 34 PSI on the majority of vehicles out there. A good tire pressure gauge is something everyone should own.

If you’re driving a vehicle with low tire pressure on any or all the tires, it creates more wear and resistance for those tires. This causes the engine to work harder to make up for the additional resistance, which means more fuel will need to be used to power the engine.

5) Bad Oxygen Sensor

bad oxygen sensor

Your engine has oxygen sensors which keep track of the mixture of air and fuel in the internal combustion chamber. Based on what it senses, it tells the powertrain control module to add the correct amount of fuel.

But if the oxygen sensor is faulty, the system may automatically add more fuel even if the engine doesn’t need it.

6) Old Engine Oil

low oil symptoms

Not only do your spark plugs need to be in good shape, but you must ensure that you regularly change the oil and replace the oil filter as well. Over time, engine oil becomes thicker and has different flow properties.

Because of this, there is increased resistance within components of your engine. This leads to more fuel being needed to move a vehicle.

See Also: How to Dispose of Old Gasoline

7) Improper Gear Changes

gear shifts

This is especially true with manual transmissions but also applies to automatics with sport modes. Don’t change gears too early or too late. If you try to upshift at too low of an RPM, the engine has to work harder to accelerate.

Alternatively, if you constantly let your engine run in the upper RPM range in your powerband since you enjoy the extra power, keep in mind that you’re also burning a lot more fuel.

8) Driving Too Fast

car won't accelerate

Believe it or not, the difference between going 80 MPH and 70 MPH could mean the consumption of 25% more fuel. The two biggest factors that contribute to this are wind resistance and gear ratio. That is why it is always best to just drive the speed limit or be as close to it as possible. Otherwise, you will be using up more fuel than needed.

In addition, don’t gun it off the line every time when the light turns green. Smooth acceleration will save you a lot of fuel, especially when there’s another red light a couple blocks ahead.

9) Air Conditioning

air conditioning

When you use the air conditioner, more demand is put on the engine. As a result, it must burn more fuel to meet this demand. Use standard ventilation from the blower if possible or simply roll down your windows when driving at slower speeds like on typical city streets.

Keep in mind that driving with your windows open also burns more fuel because the openings create a dragging effect which slows the vehicle down. This is especially true at higher speeds such as on the highway. In that case, using the AC is the better option.


21 thoughts on “9 Causes of Poor Gas Mileage (Increase Your MPG)”

  1. My car Lexus Rx 330, is consuming a lots of fuel and also when you touch the exhaust pipe it always stain with black smoke mix with fuel.

  2. My Subaru legacy B sports consume fuel consumption I have changed Sparks plugs buy a new Air cleaner, Clean Throttle, Fix up exhaust pipe, changing Oxygen sensor still a car using 1 littre of petrol for 5 km

    • If there are any check engine lights, get those addressed first. If not, make sure you are up to date on all your routine maintenance. Check the condition of the spark plugs, replace the fuel filter, and make sure you keep a healthy following distance if you’re routinely driving in traffic.

      • Tried to tell wife about breaking late but difficult my thought if you going forward when breaking then you use more fuel

  3. my car have just started excessive fuel consumption. I wonder how I can see what the problem is amongst the list.

  4. I have a Mitsubishi canter 3,5 ton truck powered by Mitsubishi 4g54 petrol engine 2,6l ..the truck uses a lot of oil and petrol in an abnormal way.. A trip from cape town to Jo’burg cost 8 full tanks and additional 5l of oil ..I didn’t have a load on ..the engine was completely redone before the trip by a reputable workshop ..I still can’t figure out what might be the problem ..will appreciate a lot if there is anyone with experience with this type of engine..perhaps that’s just its nomarl consumption..

    • If your catalytic converter is clogged, it will block exhaust flow which will reduce power and increase fuel consumption since your vehicle is trying to overcome the blockage. This condition can be dangerous if the catalytic converter gets too hot, as they can catch fire when obstructed.

      Sometimes a vehicle will throw a code related to the catalytic converter when the oxygen (O2) sensor has gone bad. If an O2 sensor malfunctions, a vehicle will often run rich to compensate for the lack of sensor data. Running rich means more fuel is injected than necessary, which increases fuel consumption.

  5. Thank you so much for your help…this information is of great help as iv been refilling my car fuel regularly…like in a week I have to use 1150rands on fuel


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