You put diesel in your gas engine? Hey, it happens! You’re not the first and definitely won’t be the last. It’s a mix-up that might make your heart race a little, but don’t panic—you can fix it. I’m here to walk you through it step-by-step, like a buddy by your side. This article will show you exactly how to clean out that diesel and get your engine happy again.
Understanding What Happens When Diesel is in a Gas Engine
What Diesel Does Inside a Gas Engine
Putting diesel fuel into a gas engine causes more than just a weird smell. Diesel and gasoline are completely different types of fuel. Gasoline is more flammable and made for quick, spark-based ignition. Diesel is heavier and needs compression to ignite. So, when you put diesel in a gas engine, it doesn’t ignite the way gas should. Instead, it can clog parts of your fuel system, cause your engine to sputter, and potentially lead to stalling or even internal damage if not addressed quickly.
The engine might not start, or it may run roughly. Sometimes, it might just stall out and refuse to start again. That’s because diesel doesn’t vaporize easily like gasoline, so your spark plugs and injectors can’t handle it well. It also leaves oily residue in parts of the engine that are meant to stay clean.
Spotting the Symptoms of Diesel in Your Gasoline Tank
If you’ve accidentally put diesel into your gas car, you might notice some signs quickly. The first is usually difficulty starting the car. If it does start, it might run rough—like it’s coughing or struggling to stay alive. Other signs include:
- Excess smoke from the exhaust
- Unusual knocking sounds
- The smell of diesel from the engine
- Poor acceleration or sluggishness
The more diesel you’ve added, the more severe the symptoms become. If you only added a small amount, your car may still run, but with a reduced performance. If you filled your tank with mostly diesel, chances are the car won’t run at all.
Why It’s Important to Act Quickly
The longer diesel stays in your gas engine, the more potential it has to cause harm. Diesel can gum up your spark plugs, coat your fuel lines, clog the fuel filter, and even damage your catalytic converter if the contaminated fuel is burned.
Acting fast can prevent major engine problems and save you from a costly repair bill. Even if your car still runs, don’t assume it’s safe. The best step is to stop using the vehicle and start the flushing process immediately.
Draining the Fuel Tank Properly
Getting Your Tools and Workspace Ready
Before you get started, it’s important to gather the right tools. You’ll need:
- A siphon pump or fuel transfer pump
- A large drain pan or fuel-safe container
- Safety gloves and goggles
- Jack stands (if you need to access under the vehicle)
- A socket set or screwdriver, depending on your fuel tank’s setup
Make sure you’re working in a well-ventilated area, preferably outdoors. Gas and diesel fumes can be dangerous, especially in closed spaces. Always work away from flames, sparks, or cigarettes.
Also, keep in mind that you’ll need a safe place to dispose of the contaminated fuel. Most auto parts stores or hazardous waste facilities will accept used fuels.
Using a Siphon Pump to Remove Diesel
The easiest way to get the diesel out is by siphoning it using a pump. Here’s how:
Insert the intake hose of your siphon pump into the fuel tank through the filler neck. Place the output hose into your drain container. Start pumping manually (or turn on the electric pump if you have one). Continue until the tank is as empty as possible.
This process might take several minutes depending on how full your tank is. You want to get out every drop you can because even a small amount of diesel can cause issues when mixed with gasoline.
If your car has a fuel tank with a screen or flap that blocks the siphon hose, you may need to access the fuel tank from underneath or through the rear seat, depending on your car’s make and model.
Dropping the Fuel Tank for a Full Drain
For a thorough flush, especially if the tank is almost full of diesel, you may want to drop the fuel tank. This is a bit more labor-intensive but allows for a better clean. Here’s how:
Jack up your car safely and secure it with jack stands. Locate the fuel tank (usually at the rear under the car). Disconnect the fuel lines and remove the bolts or straps holding the tank. Carefully lower the tank and drain the remaining fuel into a container.
Once it’s drained, you can clean the inside with a bit of fresh gasoline to rinse out any leftover diesel. Swirl the gasoline around inside the tank and then pour it out.
This method ensures you’ve removed nearly all traces of diesel, giving your car a clean slate.
Cleaning or Replacing the Fuel Filter
Your fuel filter will likely catch some of the diesel, which can clog it. After draining the tank, locate your fuel filter and inspect it. If it looks gummed up or smells heavily of diesel, it’s best to replace it.
Replacing a fuel filter usually involves disconnecting it from the fuel line, removing it from its bracket, and installing a new one. Always install it in the correct flow direction—there’s usually an arrow on the filter indicating which way the fuel should go.
A clean fuel filter ensures that the new fuel flows smoothly and that no diesel residue gets into your engine again.
Flushing the Fuel Lines and Injectors
Why Fuel Lines Need to Be Cleaned
Once you’ve removed diesel from the tank, it’s important to remember the rest of the fuel system might still contain diesel. Fuel lines, rails, and injectors could all have traces of diesel in them.
Diesel can leave oily deposits and may clog injectors or coat internal parts with soot. Even small amounts can lead to misfiring or hard starting if not cleared.
That’s why flushing your fuel system is so important—it gives your engine a fresh start and prevents damage down the road.
Using Fresh Gasoline to Flush Lines
After reinstalling the cleaned or new fuel tank, pour in about one to two gallons of clean, high-octane gasoline. This small amount of gas will help flush the system.
Turn the ignition to the “on” position without starting the engine a few times to get the fuel pump to cycle the clean gas through the lines. This process helps push out any remaining diesel in the system.
Then, remove the fuel line connection at the engine’s inlet (usually near the fuel rail or injector system) and catch the fuel in a container as it flows out. Once you see clear gasoline with no diesel odor, you can reconnect the line.
This ensures that only clean gas is reaching your injectors and combustion chamber.
Cleaning the Fuel Injectors
Diesel can clog fuel injectors in a gas engine. If the engine still runs rough after flushing the tank and lines, the injectors may need attention.
You can use a fuel injector cleaning kit, which usually includes a pressurized can of cleaner and an adapter hose. These kits connect to the fuel rail and send cleaner through the injectors directly.
Run the cleaner through the engine (as directed on the kit), and it should help dissolve diesel residue. If this doesn’t help, you may need to remove the injectors and have them cleaned professionally or replaced.
Injectors are key to performance, so taking care of them is worth the effort.
Restarting the Engine and Monitoring Performance
Refilling the Tank with Fresh Gasoline
Once you’ve flushed and cleaned everything, it’s time to fill the tank back up. Use fresh, high-octane gasoline (preferably 91 or above) to give your engine the best possible restart.
Filling the tank dilutes any remaining traces of diesel and ensures smooth fuel delivery. It’s also a good idea to add a fuel system cleaner to the gas, just to help break down any leftover diesel particles.
Use at least half a tank of gas for the first fill-up to give the system a good purge.
Starting the Engine Carefully
With clean fuel in the system, turn the ignition key and see how your engine responds. It might take a few tries to start if there’s still a bit of diesel in the combustion chamber or injectors.
Let the engine idle for a few minutes while you listen for any unusual sounds. If it runs smoothly, that’s a good sign. If it stutters or knocks, turn it off and consider checking the fuel lines or injectors again.
A few small hiccups at first are normal, but it should settle down quickly.
Watching for Warning Signs
After everything is up and running, keep an eye on your dashboard for any check engine lights. If you see one, use a basic OBD-II scanner (available at most auto parts stores) to read the code.
Keep listening to how your car runs. Is it smooth? Are there any jerks or hesitation? Strange noises? If something doesn’t seem right, it’s better to get it checked sooner than later.
Driving gently for the next 50–100 miles is also a good idea. Let the car gradually adapt back to proper gasoline performance.
I hope this guide helped you fix the diesel-in-gas mistake and saved you a trip to the mechanic. You took the right steps, and your car is on its way back to normal.
Frequently Asked Questions (FAQs)
Is it okay to drive a gas engine with a little diesel in it?
It’s not recommended, even if it’s just a little. Diesel can still harm the spark plugs and fuel system of a gasoline engine. Even small amounts can reduce performance and cause long-term wear. It’s always better to be safe and flush the system completely rather than risk permanent damage.
Can diesel damage spark plugs in a gas engine?
Yes, diesel can coat spark plugs with oily residue, preventing them from firing properly. This can lead to misfires, poor fuel economy, or even prevent the engine from starting at all. Replacing spark plugs after flushing out diesel is often a good idea.
Do I need a mechanic to flush out diesel?
Not necessarily! If you’re comfortable working on your car and have basic tools, you can handle this on your own. However, if you’re unsure or the car still doesn’t run after cleaning, a mechanic’s help might be necessary to inspect deeper damage.
Is it dangerous to mix diesel and gasoline?
Yes, mixing them can cause engine damage and performance issues. Gas engines rely on quick ignition, and diesel burns differently, which disrupts how the engine works. It’s not just a performance issue—it can lead to expensive repairs if not fixed quickly.
Can I clean the system by just adding more gasoline?
No. While adding gasoline might dilute the diesel, it won’t remove it entirely. Diesel still coats fuel lines and injectors. A proper flush is needed to get all of it out. Skipping the clean-up step might cause more problems later.
Do I have to replace the fuel filter after this?
Most of the time, yes. Diesel tends to clog filters designed for gasoline. It’s a good practice to replace the filter after any fuel contamination. It’s a cheap fix that protects your engine from future issues.
Is it safe to use fuel additives after flushing diesel?
Yes, many fuel additives can help clean out any remaining diesel residue. Look for products labeled as “fuel system cleaners” or “injector cleaners.” Adding these to your next tank of gas can help make sure your engine runs smoothly again.
Can diesel ruin a catalytic converter?
It can. If diesel is burned in a gas engine, the extra soot and unburned fuel can clog or damage the catalytic converter. This part is expensive to replace, so it’s best to prevent diesel from reaching that point by flushing your system quickly.