What Happens When Water Is Mixed With Gas?

by Louise Balle

Density of Water and Gas

First, it's important to understand the basics of density when you are trying to figure out what will happen when you mix water and gas. A denser substance is heavier, so it will pull to the bottom of a less dense substance. For example, helium is less dense than air, which is why it attempts to float above the air. The density of water in liquid form at room temperature is about 980 kg per cubic meter. The density of gas is about 720 kg per cubic meter. So gas is lighter (less dense) than water.

When the Two "Mix"

Due to the differing densities of water and gas, mixing cannot occur. As soon as you add water to a tank of gasoline, all of the water will settle to the bottom of the tank. The lighter gasoline will float on top. You get the same effect as you would get when you mix oil with water. So before you try to mix water with your gas to make it "stretch" picture a layering effect. You will be hurting your car more than helping.

Potential Negative Effects

Mixing water with gas can cause serious problems for your car. The gas on top may run through your system normally for a short period of time and your car will run as usual.

That is, until the gas on top runs out. As soon as the water at the bottom of the tank starts getting pushed through the fuel lines and into the fuel pump, the car will have startup problems. In fact, your car probably won't start at all, and you will have to spend hundreds or more to get the problem fixed and the water removed. Water is not flammable and cannot fire up an engine like gas does.

Also, water freezes in the winter. So you could end up with a block of ice in your tank if you add water to your gas. If the water somehow gets into the fuel lines, it will freeze and block any gas from getting through. Your fuel system could be ruined.

A small amount of water in a gas tank is not likely to cause a catastrophic problem, but should be avoided. Be sure to put the cap securely on your gas tank when you are finished pumping, and don't gas up in the rain unless you are at a covered station.

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