Should You Use Higher-Octane Fuel?

Refuelling is routine. Stations offer 90 to 97 octane depending on region, mostly 92 and 95, with 98 available in some urban areas.

Every car has a specified grade, yet many owners assume higher is better and fill up with premium. Is it?

Octane measures resistance to knock, which is set by the engine's compression ratio and ignition timing. Filling a car designed for 92 with 98 does not add power: the engine cannot exploit the extra knock resistance, combustion is not improved, and the money is wasted. In some cases the slower burn of high-octane fuel in a low-compression engine leaves more deposits.

Conversely, filling a car that requires 95 with 92 causes knock, which the knock sensor handles by retarding timing, costing power and economy. Use the grade in the handbook.

If the handbook allows a range, lower octane is fine for normal driving and higher octane helps when towing or in hot weather.