5 Symptoms Of Bad Gas In Your Car (and What To Do About It)

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Is your car sputtering, stalling, or struggling to start? Before you start thinking of racking up more credit car debt, the problem may be as simple as bad gas.

Contaminated or degraded fuel can cause major problems on your car’s performance, that can leave you frustrated or even stranded. But how can you tell if bad gas is to blame? Keep reading to learn the most common symptoms of bad gas in your car, so you can quickly diagnose the issue and get back on the road.

Signs of Bad Fuel In Your Gas Tank

1) Acceleration Issues

You’re at a stoplight and the light turns green. You step on the gas pedal, expecting a burst of acceleration, but instead… nothing. Your car hesitates, sputters, and takes its sweet time getting up to speed (or doesn’t accelerate at all).

If this sounds familiar, bad fuel could be the culprit behind your car’s poor performance.

2) Rough Idling

When a car is idling, it should run smoothly at a consistent RPM without any unusual sounds or vibrations. If you experience rough idling, such as sputtering, shaking, or even stalling, it could be a sign of bad fuel.

The contaminants in the fuel can cause inconsistent combustion, leading to these symptoms.

3) Abnormal Speed Changes

Driving with bad fuel can feel like riding a rollercoaster, but without the fun. One moment, you’re cruising along at a steady pace, and the next, your car suddenly surges forward or loses power altogether.

These erratic speed changes can be both frustrating and dangerous, making it difficult to maintain control of your vehicle. If your car seems to have a mind of its own when it comes to speed, fuel quality is definitely one of the things to check.

4) Poor Fuel Economy

If you notice that your car is consuming more fuel than usual or your mileage has decreased significantly, it could be due to contaminated fuel.

Simply put, bad gas doesn’t burn as well as good gas. The result is that more fuel has to be used to provide the same level of energy as with good, clean fuel. The engine has to work harder to compensate for the poor-quality fuel, resulting in increased fuel consumption.

5) Damaged Fuel Filter

The fuel filter is responsible for making sure that dirt, debris, and other contaminants don’t make their way into a car’s engine. If that happens, devastating results can occur.

So, if you have a damaged fuel filter, the actual filtering process may not be occurring and the result is compromised gas getting being used for the combustion process. It’s a good idea to periodically check your fuel filter to make sure it is working as it’s intended.

6) Check Engine Light

If your car’s check engine light come on, it could be a sign of various issues, including bad fuel. Via sensors like O2 sensors, your vehicle can detect fuel related problems and trigger the check engine light.

If you notice this light illuminating along with other symptoms of bad fuel, the first thing to do is get your car scanned for any stored trouble codes. You can use your own scan tool, have your local auto parts store scan it for you, or make an appointment with a repair shop or dealership service center.

Trouble codes are essentially very helpful clues that will help you pinpoint the problem, whether it be fuel quality or something completely different.

7) Engine Stops Running

One minute, you’re driving along, minding your own business. The next, your engine sputters, coughs, and dies, leaving you coasting to the side of the road.

If this sounds all too familiar, bad fuel could be to blame (along with other possibilities). When contaminants like water and debris in your fuel prevent proper combustion, your engine may suddenly shut down, making it one of the worst-case scenario symptoms.

8) Trouble Starting Engine

Starting your car should be a breeze. Simply turn the key (or push a button), hear the engine come to life, and off you go. But when you’re dealing with bad fuel, even the simplest task can become a challenge.

If you find yourself cranking the key repeatedly, only to be met with a stubborn engine that refuses to start, it’s worth considering the quality of your fuel. This is especially true if you’ve experienced any of the other symptoms here.

Water and other contaminants can make it difficult for your engine to achieve proper combustion, leading to starting issues that can leave you stuck in park.

How Fuel Becomes Contaminated

Fuel, whether it’s gasoline or diesel, is carefully refined for optimal performance in your vehicle’s engine. Any contamination of this fuel can lead performance and reliability issues. But what exactly causes fuel to go bad?

Water (Most Common Contaminant)

One of the most common culprits behind contaminated fuel is water. When water finds its way into your gas tank, it can wreak havoc on your engine. But how does water get into your fuel system in the first place?

Condensation is a major factor, especially if you live in a cold climate. As temperatures fluctuate, moisture can form inside your gas tank, leading to water contamination.

Another way water can get into your fuel is through a damaged water filter at the gas station. If the gas pump’s filter is not functioning properly, it may fail to remove water from the fuel before it enters your tank.

Unfortunately, there’s little you can do to prevent water contamination from a poorly maintained gas station. But fortunately, the odds of this happening is quite low (especially for newer gas stations).

But a couple ways to help minimize condensation in your gas tank is by keeping the tank at least half full and parking in a garage when possible, where the temperatures aren’t as harsh as outside.

Stale Fuel

Aside from water, fuel can also go bad if it’s left unused for extended periods. Over time, gas can degrade and lose its effectiveness, leading to starting issues and poor performance.

This is often the case with vehicles left in storage for extended periods or by using fuel from a gas can you’ve been storing in the shed or garage for years.

If you suspect that your fuel has gone bad due to age, it’s best to dispose of it properly and refill your tank with fresh gasoline.

What To Do If You Suspect Bad Fuel

If you are fairly certain that you have bad fuel in your car, take the following steps:

1. Stop driving the vehicle immediately to prevent any further damage from happening to the engine.
2. If there is only a small amount of fuel left in the tank (1/4 full or less), top off the tank with fresh fuel (preferably high octane such as “super” or “premium). This is typically all that’s necessary but it’s still a good idea to get things checked over by a mechanic to confirm no damage has occurred to your engine.
3. If the gas tank is still fairly full, have your car towed to a trusted mechanic or service center for inspection.
4. If bad fuel is confirmed, the mechanic will need to drain the fuel tank, clean the fuel system, and replace the fuel filter.
5. In some cases, additional repairs may be necessary if driving around long enough with bad fuel caused actual damage to other engine components.

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KevinKevin has been fascinated by anything automotive since his first go-kart as a kid to his time working as an auto tech for Dodge after obtaining his degree in automotive technology. When he's not working on cars or writing about them, you can find him and his E36 M3 at an event with the local chapter of the BMW CCA. Latest posts by Kevin (see all)

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