A tank full of bad gasoline in your vehicle can cause a variety of problems, including lasting damage to the engine. It is important to know the symptoms of bad gasoline because the sooner you can determine that your vehicle has bad gas, the quicker you can correct the problem. Bad gasoline typically is caused by water mixing with the fuel. To fix the issue, add a fuel treatment to the tank or manually extract the bad fuel before the engine can use it.
Determine when you last put fuel in your vehicle. Gasoline that contains a high concentration of ethanol does not have a very long shelf life and experiences what is called "phase separation" in as little as 30 days. Phase separation occurs when the ethanol and the water in the fuel bond together and separate from the gasoline. If the gasoline in your tank is more than a month old, you should assume that it is no longer good and probably needs to be drained from your vehicle's tank by a mechanic.2
Start the car. Pay attention to whether it starts properly, or if it is either struggling to start or starts and then stalls. If it has a hard time getting and staying started, and the only thing that has changed is that you just put gasoline in it, you might have watered-down fuel.3
Let your car sit and idle. Pay attention to whether it idles evenly and consistently, or if it sputters, surges or stalls out. These can all be symptoms of bad gasoline.4
Drive the car. Pay attention to how it responds when you press the accelerator. Hesitation, sputtering, coughing or loss of power are signs your vehicle might have bad fuel.5
Look at your gas gauge. If you only have a little bit of fuel and suspect it is bad, fill the tank up with a high octane (premium) fuel, then add a fuel treatment product to take care of the problem. If your vehicle has a full tank of gasoline, call your mechanic and get advice about how to handle the situation. You might need to have the bad gas siphoned out and replaced with premium gas.