Should You Buy Premium at the Pump?

Posted 8/22/16

Does buying premium gas—especially when your car doesn’t recommend it—just flush your money down the drain? With today’s gas prices and a difference between octanes that could cost up to a dollar per gallon, it’s a serious question. Ultimately, it comes down to the performance needs of your car. If you drive one of the highest-performing imported cars like a Jaguar, a Porsche, or BMW, the repair manual will probably recommend gas with a higher octane. If you drive something like a Volkswagen, however, you can probably save the extra money, as they may not require it for their stand-out performance.

Should You Consider Premium? Check the Owner’s Manual

Every car owner’s manual has a recommendation for the minimum octane for the gas you put in the car, whether it is 87, 89, 91 or even 93. For the best performance and gas mileage for your particular car, both your car manufacturer and your auto repair shop will recommend sticking with that number. Though many imported and European vehicles recommend higher octane fuel, the reason for that has more to do with your car’s performance needs than anything that has to do with the gas’ quality.  It may seem like more octane should equal better gas mileage, but it’s simply not true. If your car doesn’t call for high octane gas, you are just flushing money down the drain if you use it.

Part of Paying for a Premium Car Is the Cost of Premium Gas

Most average cars will suggest 87 octane fuel. Higher performance cars and heavy duty trucks normally require a higher octane for full performance. Serious roadsters like BMWs, Jaguars, Porsches, or Saabs almost alwaysrecommend a higher number; in that case it will be better for the car and ultimately save on fuel to use premium gas.

Don’t Bother to Fill Up With Premium When It’s Not Required

The octane of gas has to do with how much pressure the fuel can withstand before spontaneously combusting. The higher the octane, the more force it can withstand. In high performance cars—such as those with superchargers or a turbo—the fuel is compressed more severely so that the piston can fire with more power when the fuel is ignited by the spark plug. The average Honda Civic’s engine doesn’t require that type of compression, so it doesn’t need high octane gas. But, if you use lower octane in a high performance car, the fuel may combust from pressure alone, before the spark plug ignites it. This causes the pistons to fire in less than perfect timing, and may cause engine knocking. Which is not good for your high performance engine.

The engine in an average car is calibrated for that lower octane fuel. This means the spark plugs will fire before the 87 octane reaches the pressure in which it will combust without a spark. The only reason you need a higher octane is to allow for the fuel to be compressed more tightly in the engine before it fires. And if your engine never compresses that tightly in the first place, there is no reason for the higher octane. Unless you really like giving your local gas station more money.

When It Goes Wrong: Knock, Knock, Better Call a Mechanic

The good news is that in these modern times the sensors in your car’s engine are designed to ensure it is firing at maximum efficiency no matter what. Though we would never encourage putting anything other than the recommended premium fuel in your Porsche, Jaguar, or BMW, don’t worry too much if you have to fill up with a lesser octane in a pinch. The sensors will make sure the spark plugs fire when they need to—with whatever fuel you have. Keep in mind that you won’t get the performance you would normally get with premium fuel when using lower octanes.

Of course nothing is foolproof. If you hear a pinging or knocking sound in your engine, it might still indicate insufficient octane—especially if you have a vintage or classic car. In that case, check with your local Cincinnati mechanic. In special circumstances they may recommend exceeding the recommended octane level in your manual.

 

Finding a Great BMW Technician

If you own a BMW, work with a mechanic who specializes in them. Ask to see their ASE (Automotive Service Excellence) certification and see if they graduated from the BMW Step program. Remember to verify their specialty with friends and family and other BMW owners. Not every shop has the tools to perform all BMW repairs. Nor do they have the knowledge of the special care BMWs require. And make sure the shop is looking for a long term relationship. Look into the loyalty of their customers. Ask around and consult friends and family. If they care about their relationship with you, they won’t gouge you for unnecessary work.

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