Berkeley Auto Repair

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What do you know about Fuel Octane and does it matter anyway?

AudiAudi R8 V10 2016 by Mundo Velocidad, used under CC BY-SA 2.0

If you ask the average consumer what they know about octane their response would be something like higher octane is more money and not necessary; part truth and part myth. Let’s explore fuel octane and the variations.

In California there are three levels of fuel octane most frequently available; 87, 89, 91. The octane rating scale began in 1926 when a guy named Graham Edgar experimented by adding two different components; heptane and isooctane to gasoline and discovered engine knocking stopped when more isooctane was added. So he created the rating scale which goes from zero (100% heptane) to 100 (100% isooctane). Therefore fuel with a rating of 91 has more isooctane then either 87 or 89.

All car manufacturers issue a minimum octane rating for their cars. It’s important to know what your car’s rating is. While you may be able to drive with a lower octane fuel than suggested it’s not advisable especially if your car experiences any engine knocking. This is an indicator that the engine is not combusting properly and if excessive can cause engine damage.

We have seen a quite a few cars come in presenting drivability problems that have been traced to ill performing fuel components. Audis, Volvos, VWs are the makes we have seen most often with these problems. After further examination we have found many of these components were compromised by a gummy substance. This substance is likely a by-product of old fuel and fuel additives in gasoline creating a build-up of rust, water and sediment formation over time. However there is no substantial information on whether it has a link to lower octane fuel.

The appearance of the gummy substance does tend to be more prevalent in cars that use lower than recommended octane gasoline and/or cars suspected of running old gasoline. However it may be due more from the driving habits of those cars. Not enough research has been performed to know for sure the exact cause. However, to be on the safe side, we suggest using gasoline with manufacturer recommended octane rating, especially if you drive one of the following cars: Audi A4, Audi A6, Audi A8, Volvo 850, Volvo S70, Volvo V70, Volvo S80, Volvo XC70, Volvo XC90, VW Golf, VW Beetle, VW Jetta, VW Passat.

In summary, we advise using a gasoline with the fuel octane your car manufacturer recommends. If your car is non-operational for long periods of time, have the gasoline in the tank drained and replaced with fresh gasoline before you resume driving it.

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