Why Is My Car Wasting So Much Gas [9 Reasons]

With today’s fuel prices, you would have to be crazy not to want to save a few dollars. Sometimes, having a bad fuel economy can occur because of some mechanical issue and sometimes because of the driver itself.

Recently, my car started to spend more fuel than before. I wanted to find out why. So, I did pretty detailed research and found all of the reasons why my carOpens in a new tab.

Your car could be wasting so much gas because of low tire pressure, vacuum leak, leaking fuel injectors, fouled or dirty spark plugs, dirty air filters, stuck brakes, loose gas cap, always having your AC on, or bad driving habits.

Key Takeaway

Why Is My Car Wasting So Much Gas [9 Reasons]

  • Low tire pressure
  • Vacuum leak
  • Leaking fuel injector
  • Fouled or dirty spark plugs
  • Dirty air filters
  • Stuck brakes
  • Loose gas cap
  • Having your air conditioner on all the time
  • Bad driving habits

Why Is My Car Wasting So Much Gas

1. Low tire pressure

Why Is My Car Wasting So Much Gas [9 Reasons]

Driving a vehicle with low tire pressure will put additional stress on the engine and cause it to increase the RPMs resulting in a loss of miles per gallon. Inflating the tires at the correct psiOpens in a new tab.

So, why is my car wasting so much gas you wonder? A study has shown that you can improve your gas mileage by 0.6% to 3% by keeping your tires inflated as recommended by the tire manufacturer. You are losing 0.2% for every 1 psi drop per tire. Plus, driving with properly inflated tires will last make them last longer.

2. Vacuum leak

Why Is My Car Wasting So Much Gas [9 Reasons]

If your vehicle has a vacuum leak, it causes the air-to-fuel ratio to lean out. Once this happens, the oxygen sensor communicates to the electronic control unit to increase the fuel so the engine doesn’t run lean. This results in a richer fuel mixture causing poor fuel economy.

In most cases, you’ll notice the engine has a rough idle or up-and-down idle. These are all indicators of a vacuum leak. Other sources of vacuum leaks are fuel injector seals, intake manifold gaskets, and throttle body gaskets. Repairing the vacuum leak will increase mpg and fix the rough idle issues.

3. Leaking fuel injector

Why Is My Car Wasting So Much Gas [9 Reasons]

Fuel injectors spray fuel into the intake manifold at a certain angle and then that mixture of fuel and air gets burned into the combustion chamber. A leaking fuel injector will definitely cause poor fuel economy because it will leak fuel all of the time and will disrupt the precise air-to-fuel ratio. Fuel injectors can wear over time like any other car parts.

A leaking fuel injector can also cause the engine to misfireOpens in a new tab.

4. Fouled or dirty spark plugs

Having fouled or dirty spark plugsOpens in a new tab.

5. Dirty air filters

Why Is My Car Wasting So Much Gas [9 Reasons]

A dirty air filter will definitely cause bad MPG. When an air filter is dirty and clogged, that causes the engine to struggle. The air filter has a mission to filter out the air before it gets into the engine. Having a dirty air filter will lead to less air getting through the air filterOpens in a new tab.

This can even lead to lean conditions causing your engine to overheat. Replacing the air filter with a new one can improve miles per gallon by up to ten percent. It’s been reported that clean air filters can save up to thirty-two cents per gallon or add up to 23 miles per gas tankOpens in a new tab.

6. Stuck brakes

Is It Safe To Drive With a Broken Wheel Stud

Stuck brake pads and calipers may not sound like something you’ve heard of, but they will most definitely cause bad gas mileage. I’ve personally seen as much as 15 miles per gallon loss from stuck brakeOpens in a new tab.

Once you get the brake caliper guides and clips cleaned and properly installed, MPG can increase from 18 miles per gallon to 36 miles per gallon. In most cases, the brakes can get stuck as a result of greasing the caliper guide bolts.

This causes air pockets that don’t allow the caliper to rest in the correct position and results in the brake pads being pressed against the rotor. In some cases, the brake caliper can go bad and needs to be replaced. Ensuring your brake clips and caliper guide bolts are properly assembled will help yield the best fuel economy.

7. Loose gas cap

A loose gas cap will result in poor fuel economy. Although it might seem like false information, trust me, it’s true. The gas vapors will evaporate out of the gas tankOpens in a new tab.

This is the same principle as gasoline. Properly tightening your gas cap will result in a properly sealed fuel system and the gas vapors will not escape. Studies find that a loose gas cap can cause up to a 10% decrease in fuel economy.

8. Having your air conditioner on all the time

Why Is My Car Wasting So Much Gas [9 Reasons]

Air conditioners in vehicles use Freon. But, it requires a lot of electrical power in order for your air conditioner to start working. The request for such a large amount of electrical power puts additional pressure on the engine. This means that the engine is now working more in order to produce the needed electrical power, thus burning more fuel.

If you wonder why is my car wasting so much gas, here is why. It is known that driving with your air conditioner can increase fuel consumption by up to 20% because of that extra load on your vehicle’s engine. Of course, the load on the engine will depend on the size of the vehicle’s interior as larger interiors take more time to cool down.

9. Bad driving habits

Having bad driving habits is probably the biggest enemy of your vehicle’s fuel economy. If you are an aggressive driver that likes to accelerate too quickly or rev the engine while on a traffic stop, you will probably have worse fuel economy than those who drive slower.

This also goes for people that leave the car idle instead of turning it off. If you have a car with an onboard computer, you can see that some vehicles can spend up to 1 liter of fuel per hour while in idle.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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