Oil in lawn mower gas tank is an issue especially if you need to use the equipment right away. While it can be frustrating, this issue can be easily resolved.

Oil in Lawn Mower Gas Tank

We’ll explore the consequences of having oil in the gas tank, and then follow up with how to solve it.

What Happens When Oil Gets into Your Lawnmower’s Gas Tank

When oil gets into your lawnmower’s gas tank, the engine will damage, and you will see smoke and fume coming out of the mower. The machine would reduce its performance, and it would also result in clogging the fuel system.

There are several scenarios that can happen when engine oil gets introduced to the fuel inside the tank. In order to determine if the cause is having oil in the fuel tank, then you’ll need to check the situation and try to fix it, because it can be a hazard for your machine.

– Engine Damage

Lawn mower engines are designed to operate on gasoline and remember that gasoline is a volatile and combustible fuel that gives the mower engine the right amount of power.

On the other hand, oil is not used as fuel, in this case. When placed inside the tank, it can have serious repercussions, which are hazardous to the engine.

For one, the oil will not mix well with gasoline. This can leave sticky deposits in the carburetor, fuel lines, and fuel filter. These sticky deposits can cause the engine to overheat. Once this happens, the engine loses power and seizes up.

Oil Gets into Your Lawnmowers Gas Tank

In extreme cases, the engine may become damaged beyond repair. Engine repairs can be expensive. Worse, it may be necessary to replace the entire engine, if the damage is quite big.

– Smoke and Fumes

If the oil gets up through the engine and into the exhaust system, smoke and fumes usually result from this condition. This is especially concerning if it happens in an enclosed space where the matter is happening.

The lack of ventilation can cause you to inhale smoke and fumes, which are harmful to your health. Aside from health concerns, the smoke can be a symptom of clogged fuel systems or damaged engine parts.

– Reduced Performance

The oil in the tank will cause your mower to have reduced engine performance. This is because the oil will not burn properly, which means that the machine will not work efficiently. When this happens, the engine will be unable to generate the right amount of power for the lawn mower.

This means that the mower cannot cut grass as just as it has to. As a result, you may end up with uneven cutting and a very unattractive lawn, or it wouldn’t function the normal way that it should; this includes stopping once in a while and so on.

– Clogged Fuel Systems

The oil inside the tank can also cause the fuel system to get clogged up. The components inside the fuel system can also be contaminated. As a result, you may end up with an oil-soaked air filter, a gummy carburetor, or a soiled spark plug.

The oily deposits can cause the whole engine to stop running. This includes issues with starting the engine, which can be frustrating for many homeowners. They end up cleaning the fuel system or replacing it entirely, which can lead to extra costs and more issues down the line. It is even more of an issue when the lawn mower is used in humid, moist, or wet conditions.

How to Fix the Issue of Oil in Mower’s Gas Tank?

To fix the issue of oil in the mower’s gas tank, prepare the necessary tools, disconnect the plug, follow the fuel line to the carburetor, and detach it. Then, drain the contaminated gas, clear the tank, reattach the fuel line, fill it with clean gas, and reconnect the plug.

– Prepare the Necessary Tools

The tools you’ll need for this task are relatively simple and should be found in most tool kits. Pliers or wrenches to help you loosen the fuel line. Additionally, you can use these to remove the fuel line from the carburetor.

If your mower does not have a fuel line, you’ll need a siphon pump, tubing, or even a turkey baster to drain the tank, this is necessary to absorb all the spilled liquid.

Flathead screwdrivers can help you manipulate and reach into areas that may be hard to reach. Aside from this, you’ll need a fuel-safe container to hold the gas drained from the tank. Ensure that this container is large enough to hold all of the gas inside.

You’ll need some rags or paper towels to wipe off excess oil and debris. Ensure that these can fit inside the tank easily without leaving lint or other residues behind. And finally, you’ll need to prepare some fresh gasoline. The fresh gasoline will be used as a refill after the tank has been cleaned.

– Disconnect the Spark Plug Cable

Gently pull the spark plug hood off its terminal with a pair of pliers or just your fingers. This will ensure that your engine doesn’t accidentally start up while you’re working.

Once the hood is disconnected, place it to the side, and secure it away from the plug. To do this, you can tuck the hood with a piece of tape; on the other hand, you can find a good place to tuck away the hood and ignition cable to ensure they stay where you want them to.

– Follow the Fuel Line Leading to the Carburetor

Trace the fuel line and where it comes out of the tank. Once you spot it, follow it all the way until you reach the carburetor. Usually, the fuel line is attached to the carburetor by means of a small hose clamp.

On some lawnmowers, you may need to pop the hood open. Other models require that the mower’s seat be lifted to access the fuel line and the carburetor. Some lawn mower models even require you to remove the air filter assembly.

Fix the Issue of Oil in Mowers Gas Tank

The fuel line may be inaccessible if you’re working with a push mower. If this is your case, you’ll need to use a siphon to remove the fuel from the mower’s tank. You can use a pump readily available in many hardware stores to siphon out the fuel and remove it from the machine.

– Detach the Fuel Line

Once you find where the fuel line and carburetor join together, you must detach the fuel line. Frequently, a hose clamp is attached to the carburetor. As a result, you will need to loosen the clamp using your screwdriver.

Turn the tension screw with a few counterclockwise turns. Rotate the hose clamp gently. At the same time, pull the hose clamp away from the carburetor. Once disconnected, prepare for some gas to start dripping out.

– Drain the Contaminated Gasoline

Use the prepared gas container to collect the contaminated gasoline from the tank. You can do this by directing the fuel line to the gasoline container and allowing all the fluid to drain completely.

– Clean the Tank

Once all the fluid inside has been drained, add a bit of fresh gasoline. This will help flush out any residue. Repeat this process, of course, if you have the necessary to remove a big amount of oil inside the tank was substantial. Do this until you are sure that the tank is flushed clean of all contaminated gasoline.

– Reattach the Fuel Line

To do this, reverse the steps you follow to detach the fuel line. Return the hose clamp to its previous position and screw it tightly back into place. Now, you are fixating on the machine and its compartments, back to where they should be.

– Fill the Tank with Clean Gasoline

Double-check your fresh gasoline to ensure it wasn’t spattered by any contaminated gasoline. Once you are sure of its purity, pour it inside the tank because you now have to check the machine’s functionality after you have cleaned it properly.

– Check the Components of the Fuel System

Examine that the plug, filter, exhaust, and oil level are all clean. If they have been soiled in the process, try to clean them. If they are soiled beyond cleaning, you may have to replace them.

Lastly, check the dipstick, which measures your oil content. If the oil is adequate, let it be. Top it off with more oil if it is well below the recommended levels.

– Reconnect the Spark Plug Cable

Snap this component back to its terminal. Once you have done this, you are ready to turn on your lawn mower. When turning on your mower for the first time after cleaning its tank, expect a bit of white smoke, which is why you should examine the matter very closely, and  check if this is the residue burning off.

After a while, the smoke should clear, because no more oil will be left, as you have cleaned it.

Smooth Surface to Prevent Oil in Lawn Mower Gas Tank


A typical lawnmower can have an oil tank that may leak into the tank where gas is held. While it is concerning, this condition can be easily remedied. Here are some reminders:

  • Always check your mower to see if all parts are working correctly to avoid oil leaks in other components.
  • Work in a well-ventilated area away from electrical outlets or fire where possible.
  • Ensure that the surface is smooth and even to prevent unwanted accidents.

The next time the contents of your oil tank leak into the tank that holds the gas, you know what to look for and do. This was an easy way to clean the mower, so you should be problem-free now.

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