Premium Gas: Do I Have to Use It?

High-octane, or premium, gas doesn't boost a car's performance. In fact, you can increase the octane of gasoline by mixing in ethanol and actually decrease the potential energy in the blended fuel.

Premium helps prevent the knocking and pinging you hear when fuel ignites as it's compressed in an engine cylinder before the spark plug fires. Knocking and pinging can damage your engine. Left unattended, it can burn a hole through a piston head.

Octane ratings can be increased using additives including methyl tertiary-butyl ether, ethyl-tertiary butyl ether and toluene. Until the 1970s, tetra-ethyl lead — as in "leaded gas" — was used to boost octane ratings. Leaded gas today is a pariah fuel in most developed nations because of its links to the damaging lead levels it has contributed to human bloodstreams.

Engines with a high compression ratio — typically sport and luxury models — are more prone to knocking, which is why manufacturers of those vehicles recommend or require you use high-octane gas.

Even those instances are rare in new vehicles. Most late-model autos have microphones that listen for the distinctive sound of knocking and software that reacts to that sound by retarding ignition timing. That eliminates the knocking at the expense of some performance because the piston is farther down in the cylinder when ignition occurs. Gas delivers more power when it burns in a smaller space.

Want to see how the knock sensor affects engine operation — or to test that it's working? Find the sensor on the manifold and tap a wrench on the engine block nearby while the engine idles. You'll see the timing change briefly.

Bottom line: If your owner's manual says your warranty requires premium gas, by all means use it. If it says premium is recommended, follow your budget. If your manual says your Datsun B-210 runs on regular and you want more power, buy a new car.

© 4/30/13