You may not be aware of this, but your car is probably wasting fuel without you even knowing it. These are not just bad driving habits that you are probably already familiar with. It's about car problems that you do not even know. For example, did you know
that a possible engine misfire, incorrect oil viscosity or even slow oxygen sensors can cause your car to quickly burn off excess fuel? Even the humidity in your car's engine can be a reason to waste a lot of fuel. Let's take a closer look at the reasons for wasting fuel:

1.
Leaky / dirty injectors
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Fuel injectors fills fuel into the engine. So if a leak occurs somewhere, the engine absorbs less gasoline. This makes it inefficient, works harder, and consumes more fuel. In addition, fuel paint in your car may accumulate in these injectors, especially if you use inferior fuel injection cleaners. This causes the mixture of air and fuel to decrease, resulting in misfires and fuel waste.

2.
Faulty Oxygen sensors
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Oxygen sensors monitor the air / fuel mixture to allow the power train to increase or decrease fuel consumption when needed. If your oxygen sensors are not working properly, your engine may not be getting enough air to take it. If it does not get enough air, this will be offset by absorbing more fuel to continue the combustion. In addition, oxygen sensors become more unreliable with age and may respond less to the air / fuel content. In some cases, the computer may be told that more fuel needs to be added when it is not needed. This fuel is wasted.

3.
Engine thermostat faulty
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This small device is located between the radiator and the engine of the car. Its main task is to prevent coolant from flowing into the radiator until the engine of the car has fully warmed up - that is, when it is functioning properly. If not, gas is wasted. This is how it works: If the thermostat is faulty, it will normally not close (or not) and the coolant will continue to circulate when the engine heats up quickly. This delays the warm-up of the engine or its normal operating temperature, which may delay the operation of the power train module. This consumes more gas to compensate for the extra work.

4.
Inappropriate oil viscosity
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"Oil viscosity" is almost synonymous to the term "oil thickness". Be sure to pay attention to this, as this can also affect fuel consumption. Most late-car engines uses a 5W-20 or 5W-30 viscosity oil. It is important that the viscosity of your oil is correct. Otherwise, reduce fuel consumption by almost 5 to 10 percent by using only a higher viscosity oil.

5.
Clogged air filters
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Who would ever think that clogged air filters could waste fuel? These filters tend to get clogged with dust and small deposits, which makes the engine harder and more fuel sucks in to get the job done.

6.
Engine coolant sensor (defective or inaccurate)
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This sensor helps to monitor engine temperature and signals to the Power train Control Module (PCM) whether the engine is cold, warm or normal. When the PCM receives a signal from a defective coolant sensor, it will always be displayed cold and the computer will be prompted to grease the fuel mixture until it warms up. The problem is that once the engine warms up, it will continue to deliver fuel as the PCM is still "cold". This wastes fuel.

7.
Exhaust or converter obstacles

Exhaust systems are pipelines used to divert exhaust gases from controlled combustion in the engine. Each obstacle leads to a back pressure that requires more power and fuel.

8.
Dirty or blown spark plugs
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Spark plugs may be small, but they are important. In fact, your car does not even start without it, so you should not take it for granted. If they are clogged or worn, they can also cause engine misfires that leads to wasting fuel.

9.
Leaky EGR valve or intake manifold
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The intake manifold is the part of the engine of a car that supplies the cylinders with the air / fuel mixture. Its main function is to distribute this mixture evenly over each port in the cylinder heads. The task of the EGR valve is to return a certain part of the exhaust gas of an engine to the engine cylinders, thereby reducing nitrogen oxide emissions in gasoline or diesel engines. If the intake manifold gasket is leaking, the air / fuel mixture will be drained and the engine will ignite incorrectly, saving fuel. And if the EGR valve does not close when idling, when it is not loaded, it may cause the exhaust gas to leak back to the intake manifold, resulting in poor fuel economy and waste.

10.
Low compression

There are many reasons why your car has low compression. The piston rings may have worn or failed, the inlet or outlet valve is defective or the piston head has cracks. In any case, you could waste fuel without knowing it just because your engine no longer has the same compaction it once had.
Source:
http://www.eliancars.com/2019/11/10-occasional-reasons-why-your-car.html#more
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