Got Oil in Your Lawn Mower Gas Tank? (How to Fix)

If you get oil in the gas tank of your lawn mower, and it has a 4 stroke engine, you’re going to need to take action. While 2 stroke engines burn a mixture of oil and gas, 4 strokes solely burn gas and store their oil in a separate reservoir. Still, if you’ve got oil in your lawn mower’s gas tank, it’s not the end of the world. With a little bit of patience and the right tools, you can get your mower back on its feet right away. What you’re going to need to do if you’ve got oil in the gas tank of your lawn mower is drain it out. Failing to do this could have some pretty negative affect on your mower’s engine. Let’s get into some of the impacts that oil being where it shouldn’t be could have, and how to get oil out of a lawn mower gas tank.

What May Happen if You Get Oil in Your Lawn Mower Gas Tank

Whether you accidentally put oil in the gas tank of your lawn mower, or oil somehow mixed into it due to bad seals or damage to the reservoir, your engine won’t be happy. These are some things you might experience, and some of the potential negative impacts that oil in a lawn mower gas tank can have:

• Oil soaked air filter
• Mower billowing white smoke
• Gummed up carburetor
• Lawn mower leaking oil onto the deck
• Soiled spark plug
• Oil coming out of the lawn mower’s exhaust
• Buildup and residue inside the engine or carburetor

All of these issues could be the result of oil mixing into the fuel in your gas tank. Each one is not only something that needs to be addressed, but also something that can be damaging to the mower’s engine itself. If you notice any leaking oil, or that you’re burning oil and shooting out a bunch of white smoke, you should do some investigation.

Of course, if you already know that there is oil in your gas tank, gather all your tools and get ready to drain it. You can find a list of everything you’ll need below.

What You’ll Need to Fix This Issue (Equipment List)

To get the tainted fuel out of your tank, there are a few things that you’ll need. While there is more than one way to drain a lawn mower’s gas tank, I think that disconnecting the fuel line is the easiest and most reliable way to do so. Let’s take a look at what tools are required to do this:

• Pliers
• Flathead screwdriver
• Fuel-safe container
• Rag or paper towel
• Siphon, tubing, or turkey baster (if your mower has no fuel line)
• Fresh gas

How to Get Oil Out of Lawn Mower Gas Tank (Step By Step)

You don’t need a ton of gear to get your lawn mower’s gas tank drained, but you do need to make sure you go about doing it the right way. If you’ve accidentally put oil in the gas tank of your lawn mower, I think the best way to drain it is by disconnecting the fuel line where it meets the carburetor. But, some mowers have a carburetor that is fed directly from the fuel tank so using a siphon pump is a great second option. Here’s an overview of how to drain contaminated fuel from a lawn mower’s gas tank:

• Disconnect and secure your spark plug hood and ignition cable to the side.
• Locate where the fuel line meets the carburetor.
• Detach the fuel line.
• Collect the fouled gas in a fuel-safe container.
• Flush a bit of fresh gas through the gas tank.
• Reattach the fuel line.
• Fill the tank with new fuel.
• Check your spark plug, air filter, exhaust, and oil level.
• Reconnect the spark plug hood and ignition cable.

Now that I’ve summarized the steps you should follow when draining oily gas from your lawn mower’s tank, let’s go through each of them one by one. Just be sure to do all of this work in a very well-ventilated area, preferably outside.

1) Disconnect Spark Plug Cable

Using your fingers or your pair of pliers, gently pull the spark plug hood off the spark plug’s terminal. This is best practice whenever you’re doing any sort of work on your mower to assure that the engine can’t fire up.

Once the hood is disconnected, pull it to the side and secure it away from the spark plug. You can use a piece of tape or just find a good place to tuck the hood and ignition cable so that it won’t pull free.

2) Follow Fuel Line to Carburetor

Now, take a quick look at where your fuel line comes out of the gas tank. Once you see it, you can follow it all the way to the carburetor. It will most likely be attached to the carburetor with a small hose clamp.

On riding mowers, you might need to pop open the hood or lift up the seat to access the fuel line and carburetor. Some models even require the removal of the air filter assembly.

Also, if you’ve got a push mower, and you’re certain that it has no accessible fuel line, you should try a siphon approach to remove the fuel from the tank. Using a siphon pump is quick and easy and they can be bought at most hardware stores for about 10 bucks.

3) Detach Fuel Line

After figuring out where your fuel line and carburetor meet up, you’ll need to get the fuel line detached. Most of the time the fuel line will be held onto the carburetor with a hose clamp that you’ll need to loosen.

To do this, use your screwdriver and turn the tension screw counterclockwise a few turns. Then, gently rotate the hose clamp while pulling it away from the carburetor. It shouldn’t take a ton of effort to do this, and once the hose clamp is pulled back a little bit, you should be able to pull the fuel line off. Just be prepared for gas to start dripping out of the fuel line as soon as you disconnect it.

4) Drain Tainted Gas

Using an oil pan or other low, flat, container works well for initially collecting the gas and oil mixture that was in your tank. After your fuel line is pulled off the carb, direct the end of it into the pan and allow any fluid in the gas tank to drain completely.

5) Flush Clean Gas Through Gas Tank

Once everything in your gas tank has made its way out through the fuel line, I would recommend adding a little bit of fresh gas to the tank to help flush out any residue. You don’t need to use too much gas, but this can help get any remaining oil out of the tank and fuel line.

Though a little bit of oil residue won’t kill your engine, it can make its way into the carburetor and cause it to get gunked up. If the inside of the tank looks pretty clean after you’ve added and drained some new gas, you can move on.

6) Reattach Fuel Line

The next step is reattaching the fuel line. Basically you just need to reverse the steps you took to remove it. Stick the open end of the fuel line back on the carburetor, and then shimmy the hose clamp back to where it was before. Use your screwdriver again to tighten it firmly.

7) Fill Gas Tank with Clean Gas

With your fuel line connected, you can add your new gas. Just make sure you double-check that the gas you’re adding doesn’t have any oil in it.

8) Check Spark Plug, Air Filter, Exhaust, and Oil Level

It’s a really good idea to check these three things out before firing your mower up. If you’ve run your engine with oil in the fuel, you could have soiled your spark plug, air filter, or exhaust system.

If your spark plug or air filter has been covered in oil, your mower is going to struggle to run. Luckily these parts are inexpensive and can easily be replaced. Also, if your spark plug just has a bit of oil on it, you might be able to get away with lightly cleaning and reusing it.

The last thing to check is your dipstick. If the source of the oil in your lawn mower’s gas tank was the oil reservoir, it’s likely that you’ll need to top off the oil. Running your mower without enough oil is not a good idea.

9) Reconnect Spark Plug Cable

Last but not least, take your spark plug hood and snap it back onto your spark plug’s terminal. Once you do this you are ready to fire your mower up.

You can expect a little bit of white smoke when running the mower at first while any oil residue is burned off. This shouldn’t take long and after a while, no more smoke should be coming from the exhaust.