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What is the octane rating?
The octane rating measures petrol's resistance to self-ignition or detonation. In an internal combustion engine, petrol and air are mixed and compressed in the cylinders before ignition by the spark plug. A higher octane rating indicates greater resistance to premature detonation, that annoying “engine knocking” that can damage the engine. Imagine a boxer: the greater their resistance (octane rating), the better they can withstand blows (compression) without falling (detonating).
How is it measured?
The octane rating is measured on a scale from 0 to 100. The difference between 95 and 98 petrolis that 95-octane petrol has a resistance to detonation similar to a mixture of 95% isooctane (a very resistant compound) and 5% heptane (a compound that detonates easily). 98-octane petrol, on the other hand, resembles a mixture of 98% isooctane and 2% heptane.
The relationship between octane rating and engine power
A higher octane rating doesn't increase engine power on its own. Its real role is to allow high-compression engines to run properly — without knocking. A high-compression engine, much like an elite athlete, needs a resilient fuel (high octane) to perform at its best. If the fuel isn't up to the task, the engine won't reach its full potential, and the electronic control unit will dial back performance to protect it.
How does it affect engine performance?
The octane rating plays a crucial role in how your engine performs, especially in modern vehicles with an electronic control unit (ECU). Think of the ECU as the engine's brain — it constantly monitors a range of parameters, including detonation.
If you use petrol with a lower octane rating than recommended, the ECU will detect detonation and adjust the ignition timing to prevent it. This means it will delay the spark from the spark plug, which in turn reduces engine power and efficiency. You will notice lower acceleration, higher fuel consumption and, in some cases, even jerks or vibrations.
Over time, consistently using petrol with too low an octane rating can lead to deposit build-up inside the engine, damage to pistons and valves, and a shorter engine lifespan. On the flip side, using a higher octane than necessary brings no benefit whatsoever — it's simply money down the drain. Using the right octane rating, then, isn't just about performance; it's about protecting your engine and your budget.
High octane vs. low octane: what's the real difference in power?
It's worth being clear: a higher octane rating doesn't automatically mean more power. Engine power is determined by design, displacement, technology and a host of other factors — not just the fuel. Octane simply indicates how resistant the petrol is to detonation.
The relationship between octane rating and fuel consumption
Using a higher octane rating than recommended won't improve your fuel economy — and may even increase consumption slightly. Going back to our earlier analogy, it's like giving an athlete more water than they need: it won't make them run any faster, and could actually hold them back.
How to choose the right octane rating for your car
Choosing the correct octane rating is crucial for your engine’s performance and health. The best source of information is the owner’s manual of your vehicle. There you will find the manufacturer’s specific recommendation.
If you don't have it to hand, you can find it online through the manufacturer's website or on specialist automotive platforms. When in doubt, a trusted mechanic is always a good call.
What happens if I use a lower octane rating than recommended?
If your car requires 98-octane petrol and you use 95, the engine may experience detonation. The electronic control unit will try to compensate by delaying ignition, which will reduce power and efficiency. In addition, continuous detonation can damage the engine in the long term. It is like trying to run a marathon with an injury: not only will you perform worse, but you could make the injury worse.
What happens if I use a higher octane rating than recommended?
If your car is designed to run on 95-octane petrol, switching to 98 won't give you a power boost. The engine will run just fine, but you won't gain anything extra. Think of it like over-inflating a tyre beyond its recommended pressure: it won't make it tougher or improve its performance — and it could actually cause harm.
The bottom line is simple: use the octane rating your manufacturer recommends. No more, no less. A higher octane won't give you more power, and a lower one could hurt both performance and engine health.
Myths and facts about the octane rating
Let's clear up some of the most common misconceptions:
- Myth: "Higher octane means more power."
- Reality: Octane rating allows the engine to run correctly — particularly under compression — but it doesn't add power in itself. An engine designed for 95 octane won't perform better on 98.
- Myth: "All cars benefit from 98 petrol."
- Reality: Only cars with high-compression engines — such as sports cars or certain premium models — genuinely need 98-octane fuel. For most vehicles, 95 octane is perfectly adequate.
- Myth: "Higher octane petrol cleans the engine."
- Reality: Engine cleanliness depends on fuel additives, not octane rating. Moeve fuels include detergent and dispersant additives that help keep the engine clean, preventing deposit build-up and optimising long-term performance.
- Myth: "Mixing 95 and 98 petrol damages the engine."
- Reality: Occasionally mixing 95 and 98 will not cause immediate damage. However, it is not recommended to do so regularly, as the engine is optimised for a specific octane rating. If you need to mix, do it in small amounts and refuel with the correct octane as soon as possible.
- Myth: "Octane rating is the only thing that matters in petrol."
- Reality: While octane rating is crucial, other factors such as additive quality and fuel cleanliness also influence engine performance and longevity. At Moeve, we ensure we offer high-quality fuels that meet the most demanding standards.
To sum up: use the octane rating your manufacturer recommends. No more, no less. A higher octane won't deliver more power, and a lower one could compromise both performance and engine health. Choosing the right fuel is a smart decision — one that protects your investment and ensures the best possible driving experience.
