Here’s What Actually Happens if You Use the Wrong Fuel in Your Car

In theory, fueling up your car should be a simple process, but one glance at the gas station sign and you realize it’s not. There are so many different choices that it’s natural to wonder what happens when you use the wrong fuel in your car. This question usually comes up the first time you need to put fuel in a brand new or new to you used car

There’s not a simple, black and white answer. The result of putting the wrong fuel in your vehicle depends on the type of vehicle you’re driving and the type of fuel you’ve selected.

Mixing gasoline and diesel 

One of the most common mistakes drivers, especially inexperienced drivers, make is getting gas and diesel fuel mixed up. It’s a mistake you only make once. 

Gasoline and diesel engines are different. They have different flashpoint levels. When you fill the tank of your gas-powered car with diesel fuel, you’ll actually be able to get a few miles down the road before the car uses up the gasoline that was in the lines.

It’s not until the diesel fuel reaches the engine that you’ll discover something is wrong. The engine will completely stop working. The good news is that you haven’t completely ruined your vehicle.

All you need to do is have it towed to a mechanic, who will drain the gas tank, the fuel lines, the injectors, etc. Once they’re drained and your car has the proper gasoline, you’ll be back on the road. You can expect the lesson to cost you between $500-$1,000 plus whatever you paid for the diesel fuel. Instances of diesel fuel going into gas engines were reduced when gas stations switched the size of the pump so that it doesn’t fit into tanks of gas-powered cars.

Instances of accidentally putting gasoline in a diesel vehicle are far more common. The nozzle fits, and if you routinely drive a gas-powered vehicle and only use a diesel one occasionally, it’s easy to get forgetful. Because it takes a lot more fuel to start a diesel engine, you won’t get as far with what’s in the lines, and the damage is likely to cost more than if you add diesel to a gas engine.

The first sign you used the wrong fuel is a thick cloud of black smoke pouring out of your exhaust. The damage done by gasoline in a diesel vehicle includes engine damage, fuel line damage, and shock wave damage.

Confusing flex-fuel with gasoline

Many newer cars are designed to run on ethanol, which is called flex-fuel. More than once, individuals have inadvertently put flex-fuel into their gasoline vehicle.

While this isn’t ideal and can impact the vehicle’s ability to operate smoothly, in most cases, no long-term damage is done. Some people report that their car coughed or ran rough until they were able to fill up with gasoline. You should expect to see the check engine light come on.

Flex-fuel vehicles are designed to also operate on any type of octane gasoline, so no need to worry about that.

The wrong octane levels

Nothing will happen if you accidentally put premium gasoline in your vehicle that usually operates on regular unleaded. However, you should never try putting regular unleaded in a vehicle that is designed to run on premium.

Cars designed to use premium gasoline will develop a rattling sound when a lower octane is in the fuel lines. If you continue driving, you’ll experience severe engine damage.

Hopefully, this has helped you understand the importance of knowing exactly which type of fuel your vehicle requires and what will happen if you make a mistake.