Bad gas? What would I look for?

Specifically, what are ways to tell if it was bad gas that killed an engine, cylinder, cat?

Whether it be poor quality fuel (diluted, water or other), or even, Improper fuel type (diesel, flex fuel,???) Instead of regular, plus, premium gasoline.

I ask because my car is having severe problems after refueling. Trying to determine if that had anything to do with it.

I have a hard time believing it was purely coincidental timing... Especially with the shady behavior of the station upon informing them.

  • Welcome to Motor Vehicle Maintenance & Repair! Commented Jan 26, 2023 at 13:16

1 Answer 1


The easiest way to see if the fuel is at blame is to drain the tank and see what it looks like. About the only thing which happens with fuel is if there is water in it. That's easily discernable once you let fuel sit for a while because the water will settle down to the bottom. If you really wanted to get hard core about it, you could have a fuel sample sent out to somewhere to have it tested.

The thing to realize about bad fuel is, it isn't (for the most part) going to do any damage to your engine. It's just going to make it run bad until you have the bad fuel removed and new fuel in it's place. Depending on how bad the fuel is, it may cause you to need to replace the fuel filter as it can become clogged. If it's doing it's job, though, it will remove any particulates which may be there. Once fresh fuel is in the system and the old fuel is worked out of it (hard as you try, you won't get every drop), it should start running better ... or as good as it was before the incident. You won't know for sure if or what damage may have occurred until you do this though, so it is definitely your first step.

As far as where you got the gas from, it would be extremely hard to prove any place is at fault for bad fuel. In most cases, the best you can do is remove the bad fuel and put good fuel in. Going forward, find a station where they are very busy all the time. This ensures they are getting fresh fuel on a regular basis. You also want fuel which works in your vehicle and gives you good fuel mileage. Every car is different, so find one which works for you. When you do find it, stick with it. And definitely don't go back to the place where you got the bad fuel (I know, goes without saying, lol).

  • Thanks Paulster! However I genuinely messed up and didn't keep a sample. I'm aware that bad fuel typically won't ruin a motor, but what if it began misfiring severely (because of the fuel) and said vehicle continued on the interstate for 80 miles? I understand most people would pull over and call a wrecker, but that was unfortunately not an option. If the bad gas is removed, but the issues persist, are there ways to determine bad fuel caused these issues?
    – Mr. Hyde
    Commented Jan 29, 2023 at 14:22
  • 1
    As I stated, generally bad gas won't kill an engine or cause the main part of the engine damage. It might cause problems for peripheral components like a fuel filter or an injector, but not the main part of the engine. Also, there is just about no way to prove unequivocally a specific fuel station caused your issues. You may know down deep in your heart it was them, but feelings don't prove anything. Commented Jan 29, 2023 at 14:40
  • Could a bad injector kill a cylinder?
    – Mr. Hyde
    Commented Jan 31, 2023 at 8:38
  • 1
    If an injector is partially plugged (ie: not spitting out the correct amount of fuel), it could cause a lean condition and damage the cylinder. That said, fuel injectors are not getting plugged from bad fuel at a fuel station. It might happen over time, but not instantaneously from one tank of bad gas. Any particulates will be stopped by the fuel filter. Contaminates such as water will still pass through the system and into the engine, will cause the engine to run rough, but won't cause damage to the engine itself. Once the contaminate is cleared, it should run just fine. Commented Jan 31, 2023 at 10:45

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