- Octane rating measures fuel’s resistance to auto-ignition, reducing engine knocking.
- Higher octane is needed for high-compression, turbocharged, and direct-injection engines.
- Regular gasoline is about 87-91 RON; premium is 95-100+ RON.
- Using too-low octane can cause detonation, engine damage, and reduced efficiency.
Fueling a car represents one of the biggest monthly expenses for vehicle owners. In the current context, with fuel prices continually rising, many drivers look for ways to cut costs, and one seemingly attractive solution is fueling with cheaper gasoline, i.e., with a lower octane rating. However, this choice can have serious long-term consequences for the engine’s health.
Before making a decision based solely on price, it is essential to understand what the octane rating means and why car manufacturers recommend specific fuel types for each model.
What the octane rating represents
The octane rating is a fundamental indicator of gasoline quality and represents the fuel’s resistance to auto-ignition (the phenomenon also known as detonation or knocking in the engine). At gas stations, this number is clearly displayed on gasoline pumps and helps us differentiate between regular and premium fuel.
Measurement methods
The octane rating is determined as the average of two evaluation methods:
- RON (Research Octane Number) - the research octane rating, measured under standard testing conditions
- MON (Motor Octane Number) - the motor octane rating, measured under harsher conditions, at higher engine speeds
The higher the octane rating, the more stable the fuel is and the more resistant to auto-ignition. A fuel with a higher octane rating allows the engine to operate at optimal parameters without unwanted detonation.
Types of gasoline available
In most fueling stations in Romania and Europe, you typically find three main categories of gasoline:
Regular (Standard) Gasoline
- Octane rating: 87-91 RON
- The most affordable price
- Suitable for naturally aspirated, small-displacement engines
Midgrade (Medium) Gasoline
- Octane rating: 89-93 RON
- Intermediate price
- A compromise option for certain engine types
Premium (Super) Gasoline
- Octane rating: 95-100+ RON
- The highest price
- Recommended for high-performance engines, turbocharged or with high compression ratio
These types may be marketed under different names: unleaded, regular, super premium, V-Power, FuelSave, Ultimate, or other brand-specific labels from oil companies.
Why higher octane matters for certain engines
Modern engines, especially high-performance ones, are designed to run at parameters that require superior fuel quality. Here are the main reasons:
High-compression engines
High-performance engines compress the air-fuel mixture at very high pressures to gain more power. At high pressures, fuel with a low octane rating can auto-ignite prematurely before the spark plug fires. This phenomenon, known as detonation or knocking, can cause severe engine damage.
Turbocharged engines
Turbochargers force more air into the cylinders, increasing pressure and temperature. In these conditions, low-octane gasoline is highly prone to auto-ignition. Modern turbo engines almost always require premium gasoline to operate safely.
Direct-injection engines
Modern direct-injection systems spray fuel directly into the combustion chamber under very high pressure. These engines are optimized for high-octane gasoline and can experience operating problems with lower-octane fuel.
Consequences of using gasoline with a low octane rating
Fueling consistently with a fuel that has a lower octane rating than recommended can have multiple negative effects:
Engine detonation
Detonation manifests as a metallic knocking sound (engine ping) and can cause:
- Piston and ring damage
- Cracking or melting of the piston crown
- Premature wear of bearings
- Valve damage
Reduced performance
The modern engine is equipped with knock sensors that detect premature ignition. When this happens, the ECU intervenes to prevent damage by:
- Retarding ignition timing
- Reducing power output
- Increasing fuel consumption
Long-term issues
- Deposits buildup in the combustion chamber
- Accelerated wear of engine components
- Increased emissions
- Rough running and rough idle
- Higher maintenance and repair costs
How to choose the right fuel for your car
The safest way to determine the correct type of gasoline is to consult the car’s official documentation:
Check the owner’s manual
The manufacturer clearly specifies in the owner’s manual:
- The minimum recommended octane rating
- The optimal fuel type
- Any restrictions or warnings
Fuel cap
Most manufacturers place a label on the fuel cap or its housing indicating:
- The recommended fuel type
- The minimum acceptable octane rating
- Any special restrictions (e.g., unleaded only)
Engine categories and general recommendations
Engines that accept standard gasoline (87-91 RON):
- Naturally aspirated, small-displacement engines (sub 1.6L)
- Older engines without modern injection systems
- Utility vehicles with simple engines
Engines that require premium gasoline (95+ RON):
- All turbocharged and supercharged engines
- Direct-injection engines
- Engines with compression ratio above 10:1
- Sports and performance cars
- Large engines (over 2.0L) with modern technology
Myths about octane rating
“Premium gasoline cleans the engine”
Although many premium fuels contain cleansing additives, the main benefit of higher octane is preventing detonation, not cleaning the engine.
“Any car runs better on premium”
If your engine is designed for standard gasoline, you won’t notice significant improvements using premium. The benefits apply only to engines that require or can benefit from higher octane.
“Can I alternate between standard and premium?”
Although not ideal, occasional alternation won’t harm the engine if it accepts both types. But for engines that require premium, constant use of standard gasoline will cause problems.
Conclusion: false economy
The apparent savings from using cheaper gasoline with a lower octane rating can become a poor long-term investment. Costs from:
- engine repairs
- premature replacement of worn components
- higher fuel consumption due to reduced efficiency
- lower resale value of the car
can far exceed the pump savings.
Our recommendation is clear: always follow the car manufacturer’s specifications. The engine of your car was designed and tested for certain fuel types, and respecting these recommendations will ensure optimal operation, engine longevity, and preservation of the warranty during its validity period. Do not risk the engine health for a short-term saving that could cost much more in the long term.