Why You Can't Easily Siphon Gas Out Of Modern Cars

You could find yourself in a situation where you need to siphon fuel from your vehicle, either in an emergency or to remove the wrong fuel that was accidentally added. But it's not as easy as it was in the old days, when you could just stick a hose down the fuel filler, nearly poison yourself by sucking on it to get the fuel flowing (yes, people really did that), or use a pump to drain the tank. 

Modern vehicles come with built-in fuel failsafes to stop thieves from running off with your gas. This includes a mesh of sorts a little inside the filler neck, prohibiting pipes from reaching the tank. If you get past that, you'll have to deal with the anti-siphon valve. When an object pushes against its ball-like mechanism, the passage closes, but during a normal fill-up, the flow of fuel moves the ball out of the way, letting gas enter the tank. This is also a safety feature that prevents fuel from spilling out in case of a rollover.

While these safety mechanisms ensure that thieves can't siphon gas using a pipe, some particularly clever ones have gotten more hands-on by drilling holes in fuel tanks to steal gas. This has become yet another item on the laundry list of things stolen from car owners, one of the most common being catalytic converters.

So you're a do-gooder trying to help a friend stranded after running out of gas, or unable to fill up because the whole neighborhood has had a power outage. There are a few ways to remove fuel from modern cars without putting a hole in the gas tank. 

If you have the proper tools and expertise to remove the gas tank, you could access the tank where the filler neck connects and draw out the fuel using a hose. Another method involves accessing the fuel rail in the engine bay by removing the fuel system's Schrader valve to draw fuel from the tank using the vehicle's fuel pump. This works by redirecting the fuel flow, since the pump normally sends fuel from the tank to the engine when the ignition is on. You would have to do this a few times, as the fuel pump switches off if the engine is not cranked. 

Removing fuel from a modern vehicle's tank is arduous, not just because of the anti-siphoning devices, but also because of their intricate fuel systems. They include one-way valves and internal barriers that let fuel flow in quickly during refueling while preventing it from being siphoned out.