Victoria Car & Vehicle Maintenance - Fuels & Fluids - Meaning of Octane Ratings



Are you wondering if high-octane gasoline for your car will improve its performance? First, recommended gasoline for most cars is regular octane, and using a higher-octane gasoline than recommended in your owner's manual provides no benefit. Some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

Only if your car engine knocks should you consider switching to a higher-octane level than the recommended fuel. Unless your engine is knocking, higher-octane gasoline is a waste of money, too. Premium gas costs 5 to 10 cents per litre more than regular, an can add a $100 or more to annual costs

Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound, which is the result of premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93).

A few car engines may knock or ping. A heavy or persistent knock can lead to engine damage. In many cases, switching to the next grade up or the premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

The octane rating of gasoline marked "premium" or "regular" is not always consistent. In the US, one state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium.

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