Contaminated fuels can cause engine drivability problem and repeat failures of fuel system components. That's why it is important to check your fuel quality to prevent these problems caused by bad fuels and to save you from profound and costly effects on your engine. 

Oxygenated fuel can help improve air quality, and the most commonly used additive to oxygenate the fuel is alcohol. The chemical used for most fuels is the ethanol, which provides the same effect on the fuel system as alcohol. 

In spite of its ability to help improve air quality, too much alcohol concentration can cause the engine to run lean. A lean running engine has higher combustion chamber temperatures and can increase wear to items such as spark plugs, valves and seats and the fuel system components such as pressure regulators and injector nozzles.

Fortunately, you can already check your fuel quality by following these simple steps: 

1. Prepare the following for testing:

• Fuel sample from the vehicle you want to test. It is recommended to use a special siphon hose to remove fuel from your tank.
• Glass cylinder that is graduated in milliliters. Your graduated cylinder should hold 100 mL and have a cap to prevent tainted results.

2. Once you have your materials ready, fill your graduated cylinder to the 90 mL mark with the fuel sample, and add 10 mL of water to bring the total contents of 100 mL.

3. Snap the sealing cover over the end of your cylinder and shake the mixture thoroughly for about a minute.

4. After shaking the mixture, place the cylinder to a level surface and allow the solution to settle so that the different fluids separate.You can wait for an hour or two before examining the cylinder.

Since water is heavier than gasoline, the water will settle to the bottom of the cylinder along with the alcohol that is in the fuel. If the fuel contains any alcohol, the water level will be greater than the initial 10 mL that you pour. Then, if the new watermark exceeds 20 mL on the graduated cylinder, that means there are more than 10% of alcohol concentration on your fuel. 

In that case, you should immediately replace your fuel along with your fuel filter to avoid experiencing any problems caused by having too much alcohol in your fuel.