How to Siphon Gasoline

Whether it be for a generator or a vehicle, at some point your quality of life will be greatly improved by having access to gasoline. But where do you get it? There might be some in the underground tanks at a filling station, but this tends to be a bit more difficult to access. There might be some in abandoned vehicles on the side of the road. But how do you get it out of either container? It’s likely that you don’t have an electric pump to extract the fuel and it’s unlikely that the filling station will have power to operate the pumps. Enter the siphon. 

How a Siphon Works

A siphon is a very simple tool used as far back as the ancient Egyptians. The premise is that you use a tube to move liquid from one container to another. The tube you use is placed in a U shape with each end of the tube facing downward into each of the recepticles (the longer end of the tube being placed in the receiving vessel). There should be liquid in the tube at this point and when let free to do what it will, the liquid will begin to flow into your receiving vessel. This is due to our old friend gravity. Look at the tube, the longer leg of the tube has more liquid in it, thus more mass, and therefore gravity exerts a stronger force on it, causing it to fall into your receiving container. Gravity gets this party going, but dynamic fluid pressure is what keeps it going. Dynamic fluid pressure is the pressure exerted by a moving fluid. Since the liquid falling into the receiving container is exerting a higher dynamic pressure (greater gravitational acceleration and eventually greater velocity = greater pressure), it causes the liquid in the other leg to follow it. Now the liquid from the shorter leg is in the longer leg free falling into the receiving container, which in turn cause liquid in the source container to flow into the tube for the same reason. This creates a cycle that will only be broken when the source recepticle is empty or cavitation occurs (this isn’t likely in this scenario so I won’t even explain it). 

How to Siphon Gasoline from a Car

Applying the principles discussed, siphoning gasoline from a vehicle should be no problem. Place on end of your hose into the fuel tank via the refueling hole on the vehicle. Make sure to feed it as far in as possible. Place the receiving container lower than the fuel tank of the vehicle. At this point you have 2 choices on how to prime the siphon. You can either create a vacuum by sucking the first bit of fuel through the hose, or you can fill the hose with water. I highly recommend sucking gasoline from the tank even though you may end up with a mouthful of it (not a pleasant sensation, trust me) because water can ruin the gasoline, causing the fuel to oxidize much faster than normal. Either way, once your priming liquid reaches a point lower than your fuel tank, you should be able to drop it in your container and watch the fuel flow!

Stale Gasoline

Yes, there is such a thing as stale gasoline. But is it that serious of a problem? Yes and No. Gasoline can be considered “stale” very shortly after processing. This is because the more volatile chemicals in gasoline will have evaporated and decomposed. These compounds improve combustion and improve fuel efficiency, so if they aren’t present it’s not the end of the world, it just means your fuel economy is downgraded. That’s the part we don’t really care about, fuel is fuel and whether you lose a few miles per gallon or not is not a concern. 

The big concern is oxidation. If the fuel you collect is oxidized this can cause much bigger problems. You can tell if the gasoline has begun to oxidize because it will have a particularly sour smell and will be a darker color than normal. Once it begins to oxidizes, gasoline will start to have particles of a gummy substance that can cause a build up in your fuel system, which can cause your engine to cease working. You could try to filter these particles out, but its a lot of work for something that only may work. 

You also have to worry about water contamination. Getting water in your fuel can cause a decrease in performance and, at worst, can cause your fuel lines to freeze and potentially burst. There is a simple solution: add isopropyl alcohol to your fuel. Simple rubbing alcohol will bind with water molecules to create a combustible compound which will then burn off in the engine. 

Further Reading