Is There Such a Thing as Bad Gas?

Your car runs sluggish or even stops and starts in fits. Could it be because of bad gas? Let’s look at the possibilities.
February 13, 2018

Your car has trouble starting…the ride is sluggish and the engine “pings”…it suddenly stalls and the engine light comes on…it abnormally continues to sputter even after it is turned off…and your first thought is: I must have filled up with “bad gas.”

Is there such a thing as “bad gas”? And if so, how can you avoid it? First, let’s look at the possibilities related to how your fuel may be causing these problems:

  • The fuel has a high water content. Gasoline today typically has 10% ethanol content, and ethanol attracts water molecules. A few drops of water won’t necessarily hurt, but greater water content from issues related to delivery or storage—or the fueling itself—could present a potential problem  
  • Small particles or sediment mixed with the fuel. Filters on fueling nozzles capture most larger sediment particles but smaller particles could potentially get through and build up on the engine parts over time.
  • The vehicle was filled-up with a lower octane level than required by the auto manufacturer. This could be caused by accidentally or intentionally fueling up with a fuel that has a lower octane rating that required for the vehicle—or could be because the fuel in the underground storage tank is a lower octane level that stated, which would be unusual.
  • The gas has simply broken down. Gasoline is a complex mix of several different substances and over time it can break down into these various elements that include fuels and solvents to aid the combustion process.

The term “bad gas” is associated with conditions where the fuel does not combust properly. Vehicles get their power from a complex combustion process in which ignition depends upon high-quality fuel vapors being delivered to a combustion chamber. If this process is disrupted, the vapors do not combust properly and the ignition is interrupted, leading to hesitation and suboptimal performance. In extreme cases, it can lead to damage to the vehicle.

The cause of “bad gas” may not be the gas station itself. In some cases, the problem may have been caused further “upstream” during delivery or refining. While it is difficult for anyone to determine if bad gas has been purchased, there are some precautions that you can take to minimize the likelihood that you experience “bad gas.”

  • Use the right octane: Use the proper octane for your vehicle. The conditions caused by bad gas can occur when someone downgrades octane. 
  • Don’t use old gas: Gasoline stored and not mixed over an extended period of time—more than a year—will break down, whether in your tank or in a gas container. A fuel stabilizer may help extend the life of the fuel, but may not eliminate the problem.
  • Buy the fuel from a reputable station: In very rare cases, the gas you purchase may have been stolen from another location. While rare, some thieves have used modified trucks to steal fuel from an underground storage tank and resell the fuel at a steep discount. This fuel has not been stored properly and is much more likely to have significant amounts of water or sediment in it.

So how do you “fix” the problems associated with bad gas? First, check with the station where you think you may have bought the fuel. They may have had other customers who have also contacted them about problems. You may also want to have an auto mechanic analyze the fuel in your vehicle to see to determine its content. If the problem is minor, adding some octane booster or a higher octane fuel to your gas tank may be sufficient. If the problem is more severe, you may need to have the gas tank drained and the engine flushed.