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  • Sarah Rose

Premium Gasoline (or, I Know 8 Things About Cars & This is One of Them)

[Listen to an audio version of this blog here.]

I accidently put premium gasoline in my car, and now I'm poor.

Not really. But I sure will miss that ten dollars.

My car is actually an SUV: a Hyundai Tucson, which requires unleaded gasoline with a Pump Octane Rating of 87 or higher. It isn't problematic that I put premium in my car, but cars that require premium gas cannot use regular for reasons that I might tell you later. I recently took a motorcycle maintenance glass in order to not pay some sweaty, prepubescent mechanic way too much money to change my oil, and in the course of taking this class, learned the difference between premium and regular gasoline.

The most interesting thing I learned is that, if your car, like mine, requires regular gas (the 87 on the gas pump, which happens to be the cheapest option), then premium gas isn't any better for the engine. *gasp*

I found this interesting because I once dated a man who was adamant that premium was better, even though his car didn't require it. In his small reptile brain, expensive is synonymous with quality. It is a frustrating thing to be a woman who knows a total of 5 facts about automobiles, and perhaps 7 facts about motorcycles, and not because I should know more facts (I should) but because people largely don't believe the facts I do know. Men are widely trusted when it comes to mechanics for no substantial reason.

I don't find the mechanisms of cars or motorcycles that interesting, and most women don't. As Dr. Jordan Peterson succinctly pointed out, women are generally more interested in people and men are generally more interested in things. Most of us have witnessed this, though we may not have totally realized it. Generalizations are useful but often damning. When we encounter a man or woman who defies generalizations we are skeptical and wary.

So when I recently told a male friend about my newfound gasoline knowledge that is honestly not revolutionary in the slightest, he was taken aback. "Are you sure?" he asked, before grabbing his phone to ask Google if what I had just told him was factitious or not. I was annoyed but satisfied when he found that Google said exactly what I said, and the ghosts of feminists past danced joyously in their afterlives.

But here is why you shouldn't put premium in a car that doesn't need it.

#1. Engines

If you are putting gas in your car, you have an internal combustion engine. In this type of engine, the ignition and combustion of fuel occur within the engine, which then partially converts the energy from the combustion to power the engine. Inside the engine are a fixed cylinder and moving piston (photo below). When the expanding combustion gases push the piston, it rotates the crankshaft. Through a system of gears in the powertrain that I know nothing about, this motion drives the vehicle’s wheels.

There are two kinds of internal combustion engines: the spark ignition gasoline engine and the compression ignition diesel engine. Most of these are four-stroke engines, meaning four piston strokes are needed to complete a cycle. The cycle includes four distinct processes: intake, compression, combustion/power stroke, and exhaust. The primary difference is that diesel engines use air to compress and fuel to ignite while in spark ignition engines fuel is mixed with air during the intake process and a spark ignites it, causing combustion. Basically, the spark ignition engines ignite with fuel and a spark and diesel engines ignite with air and fuel. This is an important difference because diesel fuel is very different than the fuel you put in your car.

Are you bored yet? Let's move onto gasoline.

#2. Gasoline

Premium gas has a higher octane level than regular gasoline (91 vs 87). The octane rating of gasoline determines how likely it is for engine combustion to occur at the wrong time. The higher the octane level, the less likely the combustion will occur at any time other than when it was designed to occur. A "pre-ignition" or "engine knock" occurs when combustion occurs at the wrong time. Gas with higher octane rating is designed to resist the knocking, but modern vehicles are built with knock sensors that automatically change the timing of a spark plug to prevent the engine knocking in regular cars.

Higher octane doesn’t always mean better performance. Performance depends on the engine’s technology, in addition to a number of other factors. If your car manual states that your car requires premium, you have to use it or it could cause myriad problems that may not be covered under warranty if you damage your car with the regular gasoline. If your manual states that premium is optional, you can use either. If you'd rather not waste money, you can use regular and save 40-60 cents/gallon.

Wasn't that fun? During my motorcycle class, I wrote down many things and retained very few but this was one of the most interesting to me. I also learned how to clean a carburetor, change the oil, change the brake fluid, clean/change a chain, and host of other boring yet useful information.

My instructor was an awesome old man who has been working on motorcycles, cars, and even boats for many decades. His brain holds more engine knowledge than even he knows what to do with, but if you're in the Los Angeles area, check out one of his courses here.

P.S. It isn't necessary to know much about your car, but it might save you money and trouble down the road. If you're not already a member, sign up for AAA here, search for the best auto insurance here, or read a totally unrelated book about life on the road here.


Sarah Rose

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