What Happens If You Put Diesel In a Gas Car
Imagine pulling up to the pump, filling your tank, and then realizing you’ve accidentally used the wrong fuel. Don’t panic! Diesel in a gas car can leave you worried, but understanding how to handle it prevents injury and further damage to your motor vehicle.
This blog will clear up the confusion between diesel and gasoline, explaining the key differences between these fuels. More importantly, we’ll guide you through the steps to take if you accidentally put diesel in your gas engine, helping you avoid further damage and get back on the road safely.
What Happens If You Put Diesel in a Gas Engine?
Gasoline requires an octane rating of 87-91, the variance is because of fuel grade. According to the U.S. Department of Energy, “Octane rating is the measure of a fuel’s ability to resist “knocking” or “pinging” during combustion, caused by the air/fuel mixture detonating prematurely in the engine.” It has to ignite at just the right time to be efficient.
Since diesel fuel has an octane rating of 25-30, pumping diesel fuel into a gas car can lower the octane level needed and cause damage to the gas engine. The more diesel fuel pumped into the gas tank, the higher the level of diesel contamination. All of this can cause significant damage to the engine and interconnected parts that work together to make your car go.
What to Do If You Put Diesel in a Gas Engine
Don’t panic. Putting diesel fuel in a gas engine is far better than pumping gasoline fuel into a diesel engine, which can be far more risky. In that case, towing your car immediately to a repair shop for safe tank drainage is crucial.
However, let’s say you accidentally fill your gas car’s tank up with 50% of diesel. It’s quite possible your car will not start and you will need to have it towed to a garage to have the tank drained.
As soon as you realize the mistake, here’s what you should do to protect yourself and your gas engine:
- Approximate how much diesel was pumped into the gas tank. It’s helpful to know if you only pumped in a drop or 50% of the tank is now full with diesel fuel.
- Do not attempt to operate the vehicle. Minimize your risk of costly repairs by not running the vehicle. By not operating the vehicle you are avoiding the possibility of sucking up diesel into the fuel line. If you attempt to drive the vehicle with diesel in the engine, your engine could seize and may require extensive repairs as a result. Also, this requires immediate attention. Leaving diesel fuel to sit for too long can cause further damage.
- Call a garage. Contact a local garage you trust and explain the situation. They will most likely recommend draining your gas tank. Make arrangements with the garage so that when the tow truck arrives, the tow truck can directly deliver the vehicle to the garage.
- Call a tow truck. As soon as you hang up with the garage, reach out to a tow truck company to have your vehicle towed to the garage.
Difference Between Diesel and Gas
What is diesel fuel?
Diesel fuel is specifically designed to work with diesel engines and can be found most commonly in diesel engine motor vehicles. Examples of diesel engine motor vehicles include: eighteen wheelers, trains, buses, boats etc. Diesel is also a type of distillate fuel produced from crude oil.
What is gasoline fuel?
Like diesel, gasoline fuel is made from crude oil, but has slightly different additives that change its makeup. Most often gasoline fuel is mixed with ethanol. According to the U.S. Energy Information Administration (eia), “Most of the motor gasoline now sold in the United States contains about 10% fuel ethanol by volume.”
The Difference in Gasoline Fuel v. Diesel Fuel
- Diesel fuel is heavier than gasoline (larger molecules).
- Diesel fuel maintains a different density and viscosity than gasoline.
- Diesel fuel has a lower autoignition temperature than gasoline.
Something else worth nothing is that diesel engines do not require spark plugs to ignite because of the way the engine’s combustion system is designed.
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Frequently asked questions
What happens if I accidentally put diesel in a gas engine?
Diesel fuel can do real damage to a gas engine because the two fuels are chemically very different. Gasoline needs an octane rating of 87 to 91 to ignite at the right moment in a gas engine, while diesel has an octane rating of only 25 to 30. When diesel mixes into a gas tank, it drops the effective octane below what the engine needs for clean combustion, which causes knocking, misfires, and damage to the engine and its interconnected systems. The more diesel you pumped before catching the mistake, the higher the contamination and the more serious the damage potential.
What should I do the moment I realize I pumped diesel into my gas car?
Do not start the engine. Even if the car is sitting at the pump, leave it off, because running the engine pulls the contaminated fuel into the fuel line and through the rest of the system, where it can cause the engine to seize and trigger far more expensive repairs. Estimate how much diesel went in, whether it was a small splash or roughly half the tank. Call a local garage you trust, explain the situation, and arrange for them to drain the tank. Then call a tow truck and have the vehicle delivered directly to that garage. Quick action limits the damage significantly.
Is putting diesel in a gas car worse than putting gas in a diesel car?
No, the reverse is actually worse. Pumping gasoline into a diesel engine is the more dangerous mistake and requires immediate towing for tank drainage to avoid major internal damage. Diesel in a gas tank is still a serious problem, especially if you fill up substantially, but the consequences are generally less catastrophic if you stop driving the vehicle right away. Either way, the right move is the same: do not start the engine, call a garage, and have the car towed for a proper drain and flush.
Will my gas car start if I put diesel in the tank?
It depends on how much diesel got in. A small amount mixed with a mostly-gasoline tank may still allow the car to start and run roughly, though continuing to drive will damage the engine. If the tank is something like 50 percent diesel, the car will likely fail to start at all, and you will need to have it towed to a garage to drain the tank before it can run again. Either outcome is your cue to stop, not to try harder. Repeatedly cranking the engine or attempting to drive home only deepens the damage.
What is the actual chemical difference between gasoline and diesel?
Both fuels come from crude oil, but they are refined differently and behave very differently in an engine. Diesel is heavier, with larger molecules, and has a different density and viscosity than gasoline. It also has a lower autoignition temperature, which is why diesel engines can ignite fuel through compression alone without needing spark plugs. Gasoline is lighter, ignites with a spark, and in the United States is typically blended with about 10 percent fuel ethanol by volume. The two fuels are built for two fundamentally different combustion systems, which is why mixing them causes problems.
Where is diesel fuel typically used?
Diesel is the standard fuel for heavy-duty and long-haul vehicles where torque and efficiency matter more than throttle response. Common examples include eighteen-wheelers and freight trucks, trains, buses, boats, and many agricultural and construction vehicles. Diesel engines are also used in some passenger cars and pickup trucks, especially in Europe and in U.S. fleet vehicles. The engines themselves are built differently, using compression ignition instead of spark plugs, which is one reason mixing fuels causes such problems in either direction.
