Dear Car Talk: I just purchased a 2024 car that uses premium fuel. Most gas pumps have a single hose for regular and premium fuels. The hose is usually about 8-feet long.
If I buy premium, and the person before me filled up with regular, how much regular fuel am I paying the premium price for? And how much of my premium fuel is the guy after me getting? — Arthur
About a third of a gallon, Arthur.
Most gas pumps work by blending octanes right at the pump. Instead of having three to five underground tanks of fuel, a gas station would, for instance, have one big tank of 87 and one big tank of 93 and would blend them at the pump, on demand, to make everything in between.
Gasoline gets pumped out of the underground tanks and pushed, under pressure, to the gas pump, where it’s blended into whatever octane you select. That blend is then pushed through the fuel hose and the filler nozzle and into your car.
When you release the handle on the nozzle, or when the nozzle clicks off automatically when your tank is full, the fuel is shut off at the nozzle. The hose remains full of fuel.
So, if the person before you used 87 octane, the first third of a gallon you’d get would be 87 octane, Arthur.
In a tank-full of 12 or 14 gallons, that makes no difference to the car. For example, if you have a 12-gallon tank, and the first third of a gallon is 87 and the rest is 93, your overall octane would still be something like 92.83.
And if the person after you chose 87, they’d get a third of a gallon of 93 and end up with an overall octane a smidge higher than 87, which wouldn’t matter to their car either.
The department of weights and measures approved this method several decades ago, after concluding that it had no meaningful impact on cars or drivers. Although I understand how it can frost your shorts, Arthur.
The people who have to be careful, though, are motorcyclists. When you have a 3-gallon fuel tank, a third of a gallon can make a meaningful difference in overall octane. And not all motorcycles have the ability to adjust for varying octanes the way modern cars do.
So motorcyclists may have to hover around the pumps, like waiting for a table to free up at Starbucks, and pounce as soon as an Audi pulls away.
Got a question about cars? Write to Car Talk write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.
