Gasoline engines consume fuel is a phenomenon where the vehicle consumes 15-20% more fuel than the manufacturer's standard. This condition causes the engine to not produce power commensurate with the amount of gasoline burned.
According to a 2024 survey by the Vietnam Automobile Maintenance Association, 35-40% of vehicles in circulation consume 20-30% more fuel than the manufacturer's published specifications. This situation increases fuel costs by 15-20 million VND per year per vehicle. The engine operates less efficiently, with a 10-15% reduction in capacity and a shortened engine life due to overloading.
The causes of this condition come from many different factors such as: worn piston rings, driving habits, cold weather, poor quality fuel, low tire pressure, forgetting to change the lubricating oil, damaged spark plugs and ignition coils, improperly functioning oxygen sensors and dirty air filters.
Four measures to help overcome this situation include: regular maintenance, repairing faulty parts, adjusting driving habits and proper tire care.
This article will analyze in detail the 9 main causes of fuel consumption, effective treatment methods and the benefits of timely correction. From there, help you save significantly on fuel costs and protect your car's engine. Let's Thanh Phong Auto learn about!
The normal fuel consumption of a petrol engine is not a fixed number but a range of values depending on many factors such as vehicle type, cylinder capacity, engine technology and operating conditions. A B-class sedan usually has a fuel consumption of about 6-8 liters / 100km in mixed conditions, while a 7-seat SUV with a larger engine can consume from 9-12 liters / 100km or more.
Manufacturers often publish theoretical fuel consumption figures, measured under laboratory conditions, but actual figures when operating on the street are often about 10-20% higher due to factors such as traffic conditions, load and actual air resistance coefficient.
To help you visualize, below is a reference table of average fuel consumption for some popular vehicle segments in Vietnam:
| Vehicle segment | Engine capacity (liters) | Fuel consumption (L/100km) – Combined |
| Hatchback/Sedan Class A | 1.0-1.2 | 5.0-7.0 |
| BEST sedan | 1.4-1.5 | 6.0-8.0 |
| Class B CUV/SUV | 1.5-1.6 | 6.5-8.5 |
| Sedan/CUV class C | 1.5-2.0 | 7.0-9.5 |
| 7-seat SUV/Pickup | 2.0-2.5 | 9.0-12.0 |
Thanh Phong Auto's more than 10 years of experience shows that if you notice that your car has a significantly higher fuel consumption (20-30% or more) than the average for that car model, it is very likely that the engine is having a problem causing fuel consumption.
According to technical experts at Thanh Phong Auto, gasoline engines consume 10% - 40% more fuel due to 9 main reasons: worn piston rings, improper driving habits, cold weather, using low octane gasoline, insufficient tire pressure, neglecting to change lubricating oil, damaged spark plugs and ignition coils, malfunctioning oxygen sensors and dirty air filters.
Worn piston rings after a long period of operation will cause a loss of pressure in the combustion chamber, leading to a loss of power and consuming more fuel to compensate. This part plays a key role in maintaining a tight seal between the piston and the cylinder wall, preventing combustion gases from leaking into the crankcase (blow-by phenomenon) and preventing lubricating oil from bubbling up into the combustion chamber.
As the piston rings wear, the engine's compression efficiency decreases, fuel combustion is no longer optimal, forcing the fuel injection system to supply a larger amount of fuel to achieve the required torque.
Poor driving habits are one of the leading causes of unnecessary fuel consumption, which can increase consumption by up to 30%. Frequent sudden acceleration and hard braking will force the engine to work at high rpm, pumping a large amount of fuel into the combustion chamber in a wasteful way.
Similarly, leaving a car idling for too long also uses a significant amount of fuel without moving a single meter; a modern car can consume between 0.8 and 1.5 liters of fuel per hour just idling.
According to a 2023 study by the US Department of Transportation, aggressive driving (sudden acceleration, hard braking) increases gas consumption by 33% on the highway and 5% in the city.
Cold weather makes the engine take longer to reach its optimum operating temperature, resulting in a significant increase in fuel consumption in the first few kilometres. When the outside temperature is low, for example below 0°C, fuel consumption can be up to 20% higher than in warm weather conditions.
Reason:
Using fuel with an octane rating lower than the manufacturer's recommendation can cause pre-ignition, reducing performance and increasing fuel consumption. Octane rating measures the resistance of gasoline to detonation under high pressure in the combustion chamber. Modern engines with high compression ratios require high octane fuel (such as RON 95) to ensure that the fuel only ignites when the spark plug fires.
Using RON 92 gasoline for an engine requiring RON 95 will cause the ECU (Engine Control Unit) to adjust the ignition timing back to protect the engine, reducing power and fuel efficiency.
Low tire pressure is a silent culprit that dramatically increases your vehicle's rolling resistance, forcing your engine to work harder and burning more gas. According to a 2022 study by the National Highway Traffic Safety Administration (NHTSA), having just 1 PSI lower than the standard tire pressure can increase fuel consumption by about 0.3%. This means that if all four of your tires are underinflated by about 10 PSI (0.7 bar), your car could be using 3% more fuel for nothing.
Old, dirty lubricating oil that has lost its necessary chemical properties will increase friction between moving parts in the engine, wasting energy and causing the vehicle to consume more gas.
After a period of use (usually 5.000 - 10.000 km), engine oil will be contaminated with carbon deposits, metal chips and the viscosity will no longer be guaranteed. This increased friction not only makes the engine hotter but also forces it to use more energy (i.e. burn more gasoline) to maintain operation, which can increase fuel consumption by up to 1-2%.
Faulty or worn spark plugs and ignition coils will cause misfires, which result in incomplete combustion of fuel in the cylinder and waste fuel. A weak or poorly timed spark from a worn spark plug will not be able to effectively ignite the air-fuel mixture. Misfires not only cause fuel consumption of up to 30%, but also cause vibrations and damage to the catalytic converter due to raw fuel entering the exhaust system.
A faulty oxygen sensor (O2 sensor) will send an incorrect signal to the Engine Control Unit (ECU), causing the air-fuel ratio to be adjusted incorrectly and often in a rich state. This sensor acts as the “nose” of the engine, measuring the amount of oxygen remaining in the exhaust gas so that the ECU can adjust the amount of fuel injected.
A faulty sensor can “tell” the ECU that the mixture is too lean, causing the ECU to inject unnecessary fuel, increasing fuel consumption by up to 40%.
A dirty and clogged engine air filter will severely restrict the flow of clean air into the combustion chamber, altering the air-fuel ratio and forcing the ECU to inject more fuel to compensate. The engine needs a large amount of air (ideally around 14.7 parts air to 1 part fuel) to burn fuel efficiently.
When the air filter is dirty, the engine is "choked", resulting in a rich fuel mixture, reduced power and can increase fuel consumption by up to 10% on older models, while also causing black smoke from the exhaust.
Deal with fuel-guzzling gasoline engines with four main measures: regular maintenance, repairing faulty parts, adjusting driving habits and proper tire care. According to statistics from Thanh Phong Auto (2020-2024) on 3.500 cars, fully applying these 4 methods helps reduce 15-25% of gasoline consumption within the first 3-6 months..
Strictly following the manufacturer's regular maintenance schedule is the most effective way to prevent and overcome fuel consumption.
According to research by the Vietnam Association of Automotive Engineers (2023), properly maintained vehicles consume 12-18% less fuel than vehicles that skip maintenance.
Using modern diagnostic equipment such as OBD-II scanners at reputable garages will help accurately identify faulty parts that cause fuel consumption for timely repair or replacement. Parts that need to be checked first include oxygen sensors, mass air flow sensors (MAF sensors), ignition coils, and fuel injection systems.
Replacing a faulty oxygen sensor can reduce fuel consumption by up to 15-20%, while cleaning or replacing clogged injectors will ensure fuel is sprayed evenly and evenly, optimizing combustion.
According to a study by the Vietnamese Ministry of Transport (2023) on 5.000 drivers, Eco-driving helps save 1-2,5 liters of gasoline/100km (equivalent to 200.000-500.000 VND/month for a distance of 1.000 km).
Proper tire care is an important factor in fuel economy, because maintaining the correct tire pressure and ensuring tires are in good condition will reduce rolling resistance and optimize vehicle performance.
Timely fixing the problem of fuel consumption in cars brings many practical benefits to car owners such as: saving fuel costs every year, extending engine life by 2-3 years thanks to reduced wear on parts, increased operating capacity helps the car run smoother, reduced toxic emissions contribute to environmental protection and preventing traffic accidents due to technical failures.
The most popular and effective device is the OBD-II (On-Board Diagnostics II) scanner. This device connects to the vehicle's diagnostic port (usually located under the steering wheel) and can read error codes caused by ECU Record and display real-time operating data of the car sensor, helping technicians quickly determine the cause of fuel consumption.
Yes, a new car can still consume a lot of fuel in the initial period, called the break-in period. During the first 1.000 – 3.000 km, the new mechanical parts need time to grind and fit together, the friction is still high so the car will consume a little more fuel than announced. However, if this condition persists, you should take the car to the dealer for inspection.
You should do it fuel injector system cleaning , and combustion chamber periodically every 20.000 – 40.000 km. This helps remove carbon deposits and soot build-up, ensuring the injectors spray fuel and the combustion process takes place perfectly, thereby restoring performance and fuel economy.
Sure there is. Car modification often increases fuel consumption, especially when the changes involve engine performance, aerodynamics or vehicle weight, because increased power is often accompanied by more fuel injection and changes to vehicle shape can increase the aerodynamic drag coefficient.
Replacing a new engine (or a used engine from Japan) should only be considered as a last resort when the engine is too badly damaged (e.g. stripped crankcase, seized engine, cracked engine block) and the cost motor overhaul almost equal to or more than the cost of replacement. For most normal fuel consumption cases, it is much more economical to repair and replace the faulty parts.
Quality additives added to the fuel tank or engine oil can provide some benefits. Fuel additives can help clean injectors, intake valves and combustion chambers, improving combustion. However, they are not a “magic bullet” and are only a support, not a substitute for repairing mechanical damage.
Thanh Phong Auto is one of the leading specialized auto repair and maintenance centers in Ho Chi Minh City, with a team of highly skilled technicians and many years of experience in the field of handling gasoline engine problems. Especially in the field of repairing fuel-consuming engines,
Why choose Thanh Phong Auto?
In addition, Thanh Phong Auto also provides 24/7 car rescue service with professional team, modern equipment and quick response time within Ho Chi Minh City and neighboring provinces.
With the motto "Fast - Safe - Professional", Thanh Phong Auto's 247 rescue service is always ready to support you in any emergency situation.
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