Found it. Since the gas goes through the same hose as the other blends, if you're buying gas you need to get at least 4 gallons so the previous gas flushes out what was left in the hose from the previous sale, and fills enough of the container that the blend is primarily what you selected.
If you buy E15 and fill your tanks, then the next guy buys E10 and only gets 1 gallon, they might end up with a higher ethanol mix than intended, and if they use that on a small motor, like a chainsaw, it could ruin the seals.
Multiple tanks hooked up to one valve and hose vs. multiple tanks with their own separate valves and hoses.
Obviously, it's a different kind of valve in the first setup to prevent backflow into other lines, but that's probably about the extent of it. With the second setup, you probably need to run a new line and pump for each station for each gas type, compared to just tying the tanks into the one valve and pump per station.
I'm not a plumber or anything, though, so take it with a grain of salt.
There are a few stations near me that have E85, "88 octane" (which is just 12% ethanol), diesel, and three grades of gasoline. Since you can't mix those other fuels with gas the pump has four hoses and you still have to select the grade of gas.
Here's a pretty typical american pump: https://www.alamy.com/stock-photo-shell-station-gas-pump-135764267.html
You can select diesel with the green button, which comes out of the green handled hose on the left, but any other option for regular gas (87/89/93 in that picture) comes out of the right hose.
In America drastically different fuels like E85 and Diesel are dispensed with different hoses as mixing those with normal gasoline or vice versa in the wrong system could cause damage. But when it comes to different grades of just gasoline it's all the same hose. E10 or E15 are pretty much standard in many parts of the Country of Corn (USA) so they are the primary form of gasoline available for normal cars.
Every fuel has its own hose and “pistol”. Each “pump” has two or three or four hoses.
While those do exist in the States too, a single hose and "pistol" is used for all grades of gasoline and the operator presses a button to select their grade of fuel. The only time there is a guaranteed separate is between desil and gasoline:
The button leads to some interesting minor social problems. The expectation is that the use uses their hand or fingers to press the button, but the buttons are usually disgustingly dirty, so that lead many to using the tip of the "pistol" to smack the grade of gasoline which may put a drop or two of gasoline on the button. So those that come next and use their hands end up smelling like gasoline.
No longer interacting with public gas pumps is one minor joy of driving an EV.
i'm gonna be real with you buddy i have never seen a "disgustingly dirty" fuel button so I think the people in your area just grody. no offense to present company.
You never hit up a Shell station? Majority of them and independents I’ve been to have buttons that are worn through on the octane text for low grade. High octane is usually next most worn
(US) I've been to gas stations in big cities, small towns, little collections of buildings that have no official name but they have a dollar general and a gas station, etc...
I've seen several kinds.
Single hose to dispense 87-93 ("normal") gasoline, and one for diesel
One hose for normal gas, one for diesel, and one for high-ethanol
One for all gasoline types and one for diesel
One super fancy stainless-steel-clad gas station that looked like something from retrofuturism had 5 hoses, one each for 87,90,93, e15, diesel, and the farthest end pump had a line for kerosine.
Diesel are often entire separate sections of the gas station.
Most of the pumps in the US have the same hose for 87/89/92 octane pumps that are E10 (10% Ethanol) and if there is a higher ethanol like E15 or E85, they're usually a separate hose.
Probably nothing. I guess it's possible if you kept switching back and forth between pumping a gallon of premium and a gallon of regular on different pumps to try to steal a few dollars of higher grade, they can use it to give you a ticket, but I'm pretty sure they won't really care if you were just topping off a tank of gas with 3 gallons before a road trip.
I didn't know this before and it adds credence to my feeling that it's better to let my tank get below 1/4 full before filling it up, rather than continually topping it up.
Lower octane that puts in higher octane aren’t burning the fuel because higher octane needs a hotter spark to burn it all so you’re essentially wasting money or slowly killing your catalytic converter by putting in a higher octane than what your car is meant to use.
On the flip side, lower octane in a car that requires higher means the gas ignites quicker which will cause knocking and can damage the engine.
There’s probably more to it than this, but that is what I was always taught.
I fill up when I hit 1/4 tank as well. Don’t wait for it to go below though, as it can be bad for the engine with deposits and other stuff in the tank.
I would hope your car has a fuel filter installed that would never let deposits get to the injectors. (Or carb on the off chance you drive one of the last ones on the road.)
You should be filling up closer to a third. The fuel pump is cooled by the fuel and letting the fuel run too low can cause more wear and tear on the pump, causing it to fail.
Portable US gas tanks are typically 1, 2, or 5 gallon.
I usually just grab a 5 gallon (about 20L) can to fill up my lawn mower, throw some fuel stabilizer in there, and then I don't have to go back to the gas station for a long time.