16 Reasons Your Car Has Good Gas Mileage
Have you ever visited a gas station, calculated your car’s gas mileage, and found it’s slightly lower than what the EPA says it is? Have you ever wondered why your car uses up gas so quickly?
As your car gets older, many factors can lead to increased fuel consumption. Read on to find out what they are and what you can do to bring your fuel consumption back to normal levels.
What causes high gas consumption?
1) Carbon Deposits
As cars get older, carbon builds up on valves, pistons, injectors and cylinder walls. Small amounts of carbon build up is totally normal, but sometimes larger amounts can build up in critical areas.
This can affect the ability of the valves to seat properly and the pistons to seal against the cylinder walls. This reduces compression, which reduces efficiency and reduces fuel consumption.
This phenomenon tends to be more prevalent in direct injection cars. Direct injection injects fuel directly into the cylinder, whereas port injection injects fuel before the intake valve. Because gasoline is a solvent, port injected vehicles flush the intake valve, greatly reducing carbon buildup.
Carbon deposits can be removed with a good fuel system cleaner such as seafoam or walnut blast.
2) Piston Ring Wear
As vehicles age, piston rings can wear and make a poor seal with the cylinder walls. This reduces compression and reduces fuel consumption. Using the wrong oil, not having oil changes done at the right intervals, or low oil levels accelerates wear on piston rings and cylinder walls.
Constantly lurching your engine can cause this problem over time. Most oil pumps are positive displacement pumps (driven by the crankshaft), so under heavy loads the oil pump runs at lower pressure and slower speeds, delivering less oil to the vehicle’s vital components.
The solution is simple: downshift before accelerating and slowly release the clutch (if you drive a manual car).
3) Have a lead foot
It may be fun, but accelerating and pedaling negatively impacts fuel economy. In many cars, fuel consumption at full throttle is only in the single digits.
That’s by design: when you step on the gas, the throttle opens, allowing more air into the combustion chamber. The car’s Engine Control Unit (ECU) must respond by injecting more fuel to maintain the correct air-fuel ratio.
This phenomenon is exacerbated by the fact that most vehicles, especially those with turbochargers, run richer than necessary under heavy loads. The extra fuel cools the cylinders and prevents knocking.
Knock (or pre-ignition) is when fuel ignites before the spark plugs fire and can destroy an engine if it occurs under heavy load.
The obvious solution is to press the accelerator pedal slowly. That doesn’t mean you have to drive like a grandma: accelerate gradually and don’t press the accelerator at every opportunity.
4) Tailgating
Fuel economy drops rapidly if you don’t keep a safe distance. When tailgating, you have to stay behind and brake repeatedly and accelerate rapidly to avoid hitting the car in front of you.
It also creates waves in traffic, slowing you down and causing inconvenience to other drivers. If you stay calm in traffic and increase your safe distance, you will see a noticeable and significant improvement in fuel economy.
5) Cold Weather
If it’s cold outside, it will take your vehicle longer to reach its normal operating temperature. Cold temperatures make oil more viscous and less efficient. This effect is most noticeable when traveling very short distances.
Cold air is denser than warm air, so your vehicle needs more fuel to maintain the correct air-fuel ratio. In addition, gasoline additives are formulated differently in winter and summer. Winter fuel has slightly less energy per gallon. Other than moving to a warmer climate or storing your car in a garage for the winter, there isn’t much you can do to avoid the natural drop in fuel economy during the cold season.
6) Use fuel with a lower octane rating than recommended
Octane rating refers to the fuel’s ability to withstand burning under pressure. The higher the octane rating, the more knock-resistant the vehicle will be.
Some vehicles allow owners to choose between regular gasoline (about 87 octane), mid-range gasoline (about 89 octane), or premium gasoline (91-93 octane). Many of these vehicles recommend using premium gasoline. When lower grade gasoline than premium gasoline is used in these vehicles, the ECU must respond by retarding (also known as retarding or reversing) the ignition timing.
This means that the spark plug fires later in the compression stroke than normal, closer to top dead center (TDC) of the cylinder. If you run out of regular fuel and refill with premium gasoline, the ignition timing will be advanced again. Therefore, it is best to use fuel with the octane rating recommended by the vehicle manufacturer.
Note: If your owner’s manual says regular gasoline is required, in most cases using premium gasoline will not improve your fuel economy. To use higher octane ratings, the vehicle must be specially programmed.
7) Low Tire Pressure
Low tire pressure increases rolling resistance in the tire, which requires more energy from the vehicle to maintain a given speed and reduces MPG. Many newer vehicles incorporate tire pressure sensors for monitoring.
Unfortunately, they only warn you of a low tire pressure when it gets to a low enough point. You may still be running 5 PSI too low and not even know about it.
Check your tire pressures regularly using a good tire pressure gauge (like the Accutire) to ensure they are set to the factory recommended value. Most vehicles will have a sticker on the driver’s side door jamb that will state the recommended cold tire pressure for the front and rear tires.
8) Tire Replacement
Getting new tires can negatively affect gas mileage in three different ways. The heavier weight of new tires (especially if going to a larger diameter) compared to worn ones increases the friction against the road. Because of the extra effort the engine needs to propel the vehicle, more fuel is burned.
Some drivers upgrade to wider tires when purchasing replacements. The larger surface area in contact with the road creates more drag, again forcing your engine to work harder. The less pliable rubber compounds do not flex over the pavement as easily as properly worn treads.
9) Bad Alignment
Ever hit a big pothole then notice it takes more effort to keep the car pointed in a straight line? You’ll likely feel this increased effort at the pump, too.
When your vehicle is out of alignment, it takes more effort to travel in the intended direction because you end up fighting the resistance of a tire that’s not quite lined up with your steering wheel. Your tires might not even be lined up with each other!
Getting the car realigned at a trusted shop is an easy fix for this issue, and will generally make the vehicle safer overall.
10) Using Thicker Oil
Some people swear by using thicker oil on old cars to prevent leaks or reduce lifter noise, though this is not a recommended strategy. Thicker oil causes more resistance in the internal components of the engine, reducing fuel economy. In general, it is always best to use the oil recommended in the owner’s manual.
11) Overfilled Oil Level
If you change your oil and end up overfilling it, the oil level in the crankcase might just be high enough to reach the crankshaft. If this happens, the crankshaft will end up fighting its way through a pool of oil, which is wasted effort you’ll notice at the fuel pump.
12) Bad Ignition Coils, Spark Plugs, or Wires
The ignition system is critical for complete and consistent combustion. If a spark plug, plug wire, or ignition coil starts to go bad, fuel in that cylinder may not combust on every cycle, causing a misfire.
Unburnt fuel can’t be used to propel the vehicle forward, which reduces fuel economy. If you notice your vehicle has started idling rough, stumbling, or hesitating, it may be time to check the ignition system.
13) Clogged or Bad Fuel Injector
Fuel injectors are responsible for injecting fuel in a very specific way at a very specific time. If you have a faulty fuel injector or something obstructs the injector, it may still spray fuel, but it will likely spray in a pattern it wasn’t designed for.
This affects the fuel’s ability to atomize and mix with air for a complete and consistent combustion, affecting fuel economy. Sometimes injectors simply need to be cleaned, which will save you money over replacing each injector.
14) Incorrect Timing
Have you ever attempted to change a timing belt and noticed the car ran rough afterward? Always consult a professional if you do not feel comfortable tackling this job by yourself.
15) Bad O2 Sensor
If you notice a check engine light related to the O2 sensor, don’t ignore it! Most vehicles will appear to run perfectly fine with a bad O2 sensor, but will inject much more fuel than is needed, wasting gas. A new O2 sensor is a fairly cheap fix. Not only will it save you money at the pump, it’s better for the environment, too.
16) Old Engine Air Filter
Can’t remember the last time you replaced your engine air filter? It may be time to throw it in the trash and buy a new one.