Here's What To Do After Putting The Wrong Fuel In Your Car


This is one mistake that could spell disaster.

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We've all heard of someone who has made the mistake of accidentally adding the wrong type of fuel in their car. This happens more often than you think and can destroy your motor or cost a fortune to repair. But, believe it or not, you can put the wrong fuel in your car without it meaning you have to write off the vehicle, and the fear of making this mistake doesn't have to inspire you to shop for a hybrid. There are ways of fixing this issue. In this post, we'll be discussing issues such as placing diesel in a gas tank, ethanol in a gas tank, and how to fix things when there's water in your gas tank.

Engine Volkswagen

What is Misfuelling and What are the Dangers to the Fuel System?

Misfuelling is when you put the wrong type of fuel in your car's gas tank. To many, this may not sound problematic, but it can be disastrous because of the differences between gas and diesel engines. Here's why: gasoline and diesel are very different in composition and application, and as a result, the engines they power are built very differently, too. Gas engines make use of spark plugs to ignite the fuel, whereas diesel power plants generate heat through compression - each is made to function using specific fuel types, only. A misfuelling mistake can cause a serious amount of damage to the fuel system of both diesel and gas-powered cars. So, what happens if you put diesel in a gas-powered car?

How to Fix Bad Gas in Car
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Using Gas in a Car With a Diesel Engine

Putting gas in a diesel-engined car is much more serious than the converse. Diesel has lubricant properties close to that of oil, while gasoline is a solvent, so using gas instead is hazardous to the fuel pump and diesel injectors, will cause friction, and eventually damage the engine's internal parts. Gas also ignites much quicker, so even just a little bit of gas mixed into diesel will reduce the ignition point of diesel, which will cause premature detonation. The following might happen when you run gas in your diesel engine.

  • Premature detonation: Putting gas in a diesel tank will lower the remaining diesel fuel's flash point by a significant margin, leading it to ignite too soon, and cause serious engine damage.
  • Fuel system damage: Diesel fuel works almost like engine oil in a gas engine - it is used to lubricate various components in the engine. Gas, on the other hand, is thinner and can dissolve other substances, meaning it does the opposite - friction leads to wear and damage of fuel injectors and pumps.
  • Fuel sensor damage: The excess soot and heat caused by running the engine can cause important fuel sensors to get damaged and not feed the correct information to the car's ECU, resulting in even worse performance.
  • Reduction in performance: If you've put gas in a diesel car, there will be a significant decrease in performance due to an incomplete or compromised combustion cycle. A mix of these two fuels will make the car's ECU compensate by adjusting the air to fuel ratio, reducing performance.

Putting Diesel in a Gas Tank

This type of misfuel is less common, and may seem less serious than mixing gas into a diesel system, but in reality, it's also potentially critical. Upon starting your car, the diesel will coat the fuel system; symptoms of the wrong fuel in the car in this case include misfiring, excessive smoke, and will eventually lead to the vehicle not wanting to start at all. Diesel is also more dense than gasoline and will make the fuel pump work excessively hard to push the fuel through the lines, which will eventually clog up the fuel filter. The fuel injectors will also stop working and will need to be flushed. You may be able to travel for a short distance before the engine seizes. There are other potential problems that may crop up if you've put diesel in the gas tank not meant for it:

  • Diesel sinking to the bottom of the gas tank and injected into the intake manifold or cylinder can result in deposits or residue on the pistons, valves, and spark plugs
  • Blown head gasket as a result of hydro-locking in the cylinders
  • Diesel in the exhaust system can ignite in the catalytic converter, which is an expensive repair job if it blows

Running Regular in a Car That Requires Premium Gas

Now that you're feeling a little paranoid about using the incorrect fuel for your car, you may also worry about what happens if you put premium gas in the tank when it should be regular octane, or vice versa. Back in the day, running regular gas in a premium car would almost always cause engine knock due to the difference in octane, but thankfully modern cars can adapt to whatever octane is being used, with the only real noticeable consequence being a drop in performance. Modern car's ECU systems will simply adjust the engine's timing to accommodate for the lower octane rating. It won't seriously damage the vehicle, but to attain the maximum performance out of an engine, it is highly recommended to use the correct octane rating at all times.

If you want a little more clarity on what fuel octane is and the different grades of fuel available in the US, read our post on it here.

Running Ethanol/E85 in a Gas-powered Car

Ethanol and E85 are not the same thing, firstly; while ethanol is an alcohol made from corn, sugar cane or other biomass, E85 is a flex-fuel comprised of 85% ethanol and 15% regular gasoline. Certain cars today are specifically designed to burn flex-fuel, but not all cars can run it safely, including most cars built before 2008, and all diesel cars. Many trucks and sedans in the States are flex-fuel compatible, including the Silverado 1500 and Impala from Chevrolet, respectively.

Accidentally adding E85 or ethanol to the gas tank won't mean the end of the world if you top up the rest of the tank with regular unleaded gas, but running on pure E85 can cause serious problems due to its corrosive nature, especially over time, as aluminum, rubber, and magnesium parts will slowly start to erode on cars not meant to run on E85. To modify a car's fueling to accept E85 can be a costly exercise and parts that will have to be replaced include the fuel hoses, fuel pump, certain seals and gaskets, and most importantly, the fuel injectors. We have a closer look at flex-fuels of this type, here.

What if There’s Water in the Gas Tank?

Forget about using the wrong fuel in your car - getting water in your gas tank is just as serious, and a fix might end up costing you more than you bargained for. Water can get in your gas tank through cracks in the fuel cap, a bad water filter at the gas station you're filling up at, condensation in your gas tank - or if your inquisitive toddler "tops up" the tank with your garden hose.

So what are the symptoms of having water in your gas tank?

  • Sputtering or idling, as water isn't combustible and results in erratic idling soon after filling up at the pumps
  • Sudden increase/decrease in power as the engine struggles to compress the water and gains a surge when cleaner fuel is injected
  • Bad fuel economy
  • Refusal of the car to start at all

To solve this issue, it is recommended that you

  • Use fuel driers made to remove water from gas tanks
  • Siphon out the gas tank
  • Leave the tank empty for a while to dry out
  • Call in professional help, if at all possible, for best results

What to do When You've Messed Up

Now that we've covered what could happen if you've put the wrong liquid into the gas tank, the only thing left to answer is how you fix the problem, and what steps you can take to mitigate damage.

  • Do not start the car: It is imperative that you do not start your vehicle after filling up with the wrong type of fuel. Running the engine for even a few minutes can cause serious issues, especially on diesel cars that have been filled with gas. If you've already started the car inadvertently, turn it off and move to the next step.
  • Get the car to a safe location: Get someone to push your car out of the way, without starting it, in preparation for towing it.
  • Call your insurer or a mechanic: Get your insurer or a trusted mechanic to tow your car to the nearest workshop.

Most mechanics will fully drain your fuel tank and fuel system and perform a few systems flushes before handing the vehicle back to you. It is recommended that you let a professional take care of this.

Gas Station

How to Prevent Misfuelling

You'd be surprised at how often this happens. This issue can easily be avoided by being aware of some simple points, such as knowing the differences between gas and diesel engines and fuels and, more specifically, knowing what type of gas your car takes. But there are other steps you can also take:

  • Install a misfuelling device to your car: If you drive a diesel car with a similar gas tank opening to that of a gas-powered vehicle, you can fit a diesel fuel tank insert that only accepts diesel nozzles. Alternatively, a sticker or fuel cap with the type of gas printed on it can be helpful, too.
  • Be aware: Always double-check what nozzle you've inserted into your gas tank before you start pumping gas.


Misfuelling happens more often than you think and can cause serious damage to your vehicle if left unchecked. By informing yourself of your car's fuel requirements and paying close attention at the fuel pumps, you can avoid this costly mistake. Having water in your gas tank or filling a diesel car up with regular gas are the two most dangerous misfuelling scenarios, but damage can also occur when fuelling a gas car with diesel or a gas car with E85. In the event that you've made the mistake already, be safe rather than sorry - don't run the car, and call for professional help.


Can I put a small amount of petrol in my diesel car?

A small amount of petrol won't destroy a diesel motor, but it will place it at higher risk of early detonation due to petrol lowering combustion temperatures, and could hurt the fuel system. There isn't any good reason to do this, so as a rule of thumb, rather stick to the type of fuel your engine requires.

How long can diesel sit in the car?

Diesel will last for between six to twelve months before it starts to go "gummy." After this period, old diesel can clog up fuel filters and injectors.

How much does it cost to drain the wrong fuel from your car’s tank?

It all depends on the car, but you can expect to pay anywhere from $400 to $2,000 - and this is without taking into account any further clean-up, inspection, or repair costs.

How long can I drive my car with the wrong fuel

It depends on which type of fuel has been mixed into your gas tank. A gas-powered car filled with diesel will manage a few miles, while a diesel vehicle topped up with gas will present issues immediately. Gas cars will also run a good while on E85 before succumbing to fueling issues. It's safest not to run your car at all if you've topped off with the wrong substance.

Is putting the wrong fuel in your car covered by insurance?

There are many advantages to auto insurance, but one disadvantage is that many insurers generally do not cover mechanical breakdowns, but if you suspect that your vehicle has been damaged due to the incorrect fuel being supplied by the fuel retailer, it could possibly be covered. Check on your auto insurance plan whether breakdowns and misfuelling are covered.

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