Octane rating: when pricier fuel gives you nothing

Higher octane does not add power by itself; it only makes fuel more resistant to knock. Paying extra makes sense only when the engine is built for it.

• Check the owner's manual or the sticker near the filler cap: the manufacturer states the minimum octane.
• Fill up with the recommended grade or higher. Going below the minimum is risky: knock can damage pistons and valves.
• If the engine is designed for, say, 95, putting in 98 for power is pointless: without changes to the tune you won't feel a difference.
• Listen under load at low revs: a metallic ping or rattle means knock. Change the fuel and have the engine checked.
• Don't hop between fuels constantly: pick stations with consistent fuel quality and avoid filling when their tanks are nearly empty.