Is My Car Gas Or Diesel? – This is critical


It’s important to know if your car is gas or diesel. Filling up with the wrong fuel can be a costly mistake. Let’s look at how to avoid it and what steps to take if you have filled the wrong fuel.

To identify if your car is gasoline or diesel, open the fuel flap and locate the fuel label. The label will specify ‘Diesel Only’ or ‘Unleaded Only’. If the sticker is missing, refer to the owner’s manual.

In this post I’ll show you how to tell the difference between gas or diesel cars and how to tell a gas from a diesel pump at the gas station. You’ll also learn what to do if you have made an error and pumped incorrect fuel into your car.

How To Identify A Gas From Diesel Car

Gas flap specifying fuel type
Unleaded gas only sticker

The fastest way to identify what fuel type your car takes is by opening the fuel flap. Inside the fuel flap you’ll find a sticker specifying the correct fuel type. It will state Unleaded only or Diesel only. If your car isn’t new, the sticker may be missing.

If that’s the case, locate the User Manual, usually located in the Glove Compartment. Under “Fluid specifications” you’ll find the fuel type you vehicle requires.


If the User Manual is not in the Glove Compartment, call to a car dealer, repair shop or car rental company, they are around cars and will know which type engine is fitted by looking under the hood. Or you could call whomever you have borrowed the vehicle from.

What are the Different Pumps for Gas and Diesel?

Gas fill side

There are a few reasons you might be asking this question. You may be new to driving, you might be driving a rental or a borrowed car. If this is your first car and your first time to fill your tank you need to know if your car takes gas or diesel and we’ve already covered that one (sticker inside fuel flap).

But you also need to know which pump to select at the gas station and that’s what we’ll cover right now.

Being your first car, you more than likely know if it’s gas or diesel, but be sure to select the correct pump nozzle. Each pump will have a selection of nozzles to choose from. They are color coded, for your convenience but always still check the label to confirm the correct choice.

Sometimes the Diesel Pump is completely separate from the gas pump altogether which makes for safer pumping, but more often than not they share a pump.

The Diesel selection button is generally on its own and the gas selection is 2-3 buttons placed together to the other side. Regular – Super – Premium. The difference between the three unleaded is how clean they are. The Premium is going to be the most expensive, but each can be pumped into a gasoline car.

Also, a diesel pump filler nozzle won’t physically fit into a gas powered cars gas tank (modern vehicles), the pump nozzle is too big. This is by design, it prevents customers filling gas powered cars with diesel fuel.

The reverse is not true however, a diesel vehicle will accept either nozzle and as a result, it’s always a diesel vehicle that’s at risk of being incorrectly refueling with gas.

Will Gas Hurt A Diesel Engine?

As said earlier, a diesel fuel pump nozzle won’t physically fit into a gas powered car’s gas tank. As a result, it way more common for a diesel car to have gas in its tank than a gas powered to have diesel in the tank.

Gas Engines and Diesel Engines are quite different. Both are combustion engines but they differ in how they convert fuel to power. Gasoline engines mix fuel and air, which is compressed by pistons and then a spark plugs ignite the mixture.

Diesel engines compress the air first, then fuel is added at high pressure. The high compression causes the fuel to ignite.

By adding gas to a diesel engine you run the risk damaging various components. Diesel fuel contains lubricants that help lubricate diesel engine fuel system components – high pressure fuel pump and injectors. Gas doesn’t contain any lubricant, and that often causes scoring of the pump which allows fine metal fillings damage injectors, all very expensive repairs.

Exhaust system components such as sensors and filters may also be damaged by unburnt gasoline and total engine failure is also possible. The worst part, warranty won’t cover any of these repairs.

If you think you have put the incorrect fuel into your vehicle, don’t panic, I’ll tell what you need to do, and that’s what we’ll cover next.

What to Do If You Put Gas in a Diesel Engine

The most important thing is not to start your engine! If you have pumped gas into your diesel tank and then suddenly realized, all is not lost. Get some help and push your car to the side of the forecourt.

If you can, avoid even turning on the ignition because that cycles the diesel lift pump. A diesel engine has two fuel pumps, an electric lift pump (moves diesel from tank to engine) and a mechanical high pressure pump (engine driven, fuel lubricated and creates super high fuel pressure).

The high pressure pump is what’s at risk here, but only if the engine is stared. If your fuel level was low, but not very low, evening turning on the ignition shouldn’t cause gas to enter the fuel system. Since diesel fuel is heavier than gas and since the pump syphons from the bottom of the tank, you should be fine.

That said, the gas needs to be removed from the tank. That’s a messy job and can be dangerous, since gas is explosive and throws off a ton of vapors. You’ll really need to call a mechanic and tell them what you have done. Indeed many mechanics specialize in this type work and will repair your car right there at the gas station.

Alternatively the car can be towed to a garage where they can syphon out the fuel tank, clean the fuel lines and change the fuel filter. Run the engine and remove any fault codes that may have set.

No damage will have been caused to your car. However, the cost of this procedure can still run to $400 – $500 for a full fuel flush and filter.

I started the car

If you have started and ran the engine a while, the resulting damage depends on a few factors.

  • How long was the engine running before you realized?
  • Did the engine shut down
  • How much fuel did you pump?
  • How much fuel was already in the tank?

If you have just left the gas station and see plumes of black smoke coming from your exhaust, chances are you have pumped the wrong fuel. Pull in as soon as you are safe to do so and turn the engine off. There may be no damage caused.

If there was already some diesel in the tank and you haven’t pumped a huge amount, you may be able to limit some of the damage the diesel may be only lightly diluted by the gas and so it’s likely no damage has occurred.

As said earlier diesel is heavier than gas, however driving causes the gas and diesel to mix.

The further you drive with the incorrect fuel, the more damage you’re going to do to your car’s engine. Possibly irreparable damage but certainly very costly.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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