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 a pretty detailed research and found all of the reasons why my car is wasting so much gas. Here is what I found out:

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 psi will ensure that your vehicle gets the best fuel economy. A good rule of thumb is to inflate the tires to four to five psi less than their maximum.

So, why is my car wasting so much gas you wonder? 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.

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2. Vacuum leak

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 misfire. When this happens, it means that one or more cylinders have stopped producing power. You will feel that your vehicle will start to work differently and will loose power.

4. Fouled or dirty spark plugs

Having fouled or dirty spark plugs can cause vehicle to waste fuel. This happens because when the fuel is sprayed into the combustion chamber a fouled or dirty spark plugs will not ignite the fuel. When unburnt fuel is added to a cylinder and it doesn’t combust, it gets wasted. This causes bad gas mileage. Replacing the faulty spark plugs with new ones will ensure a good idle and better fuel economy.

5. Dirty air filters

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 filter and will deprive the engine from air.

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 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 tank.

6. Stuck brakes

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

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 breaks can get stuck as a result from over greasing the caliper guide bolts.

This causes air pockets which doesn’t allow the caliper to rest in the correct position and results with 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 a false information, trust me, it’s true. The gas vapors will evaporate out of the gas tank if you leave the gas cap loosen. Same thing can happen with a rubbing alcohol.

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

8. Having your air conditioner on all the time

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 to 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 at 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.

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Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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