Oil in Gas Tank May be a Mistake, Need, or Hostile Act – What to Do

Oil could enter your gas tank for several reasons. Surprisingly, while oil in gas tank could get many drivers worried, others see it as a way of having a better running engine. Generally, several fluids run your vehicle to keep moving parts working optimally.

There is the engine oil that helps cool and lubricates the engine and transmission oil that helps to keep your transmission intact. These fluids can somehow get into the gas tank, which isn’t ideal. We will discuss how oil gets into the gas tank and how to know there is oil in gas tank. But first, let’s see what you can do if you accidentally pour oil into a gas tank.

cooking oil in gas tank

What to do if you accidentally add oil to gas tank

While some intentionally pour oil into the gas tank, others do this by mistake. So if you have accidentally added oil into a gas tank, here is what to do.

First, how much oil did you pour into the gas tank? If you add as little as a quart, you may have nothing to worry about. Drive to a gas station and fill the gas tank completely with gasoline; the oil will burn out eventually as you drive.

If, however, you added up to five gallons, it’s a different game entirely. Do not crank your engine; have your car towed to a facility where they can drain out the oil-gas mixture from the fuel tank. After which, you refill with fresh gasoline.

But suppose you’ve cranked the engine, you will do much more than just draining.

If you already started your engine, the oil-gas mixture may have moved through the fuel lines and even stuck to the carburetors and spark plugs. So after draining out the contaminated fuel, drain the fuel lines and clean the carburetors and spark plugs. You also need to change your filters. After which, you add fresh gasoline to your fuel tank.

However, if your vehicle uses the two-cycle engine, oil in gas tank shouldn’t be an issue. 2 cycle engines do not have an internal oil reservoir, so both the oil and gas stays in the gas tank. Basically, these engines use the 2-cycled fuel—a mixture of gas and oil.

However, this must be in a certain ratio which in most cases is stated in your vehicle manual. Because while 2-cycle engine oil in car gas tank wouldn’t be a problem for two-cycle engines, putting too much may cause problems.

What causes gas to mix with oil?

If your gas has mixed with oil, it could be for the following reasons. But which applies to you depends on your vehicle type. So here are the reasons why gas mixes with oil.

Incomplete fuel combustion-Natural process

In internal combustion engines, all the fuel is never used up, even if it’s in the proper amount. This excess unburned fuel can run past the piston rings and enter the crankcase.

Fuel injectors are stuck in the open position.

Common in newer cars, fuel injectors help supply fuel into the combustion chamber. If any of these injectors gets stuck in the open position, it can spray out excess fuel into one or several cylinders.

Excess fuel in the cylinder will usually not get burnt during combustion. This unburnt fuel can eventually get past the piston rings and end up in your oil pan.  In other cases, when the injectors are bad, they may still pump out excess fuel even if they are in close positions.

A faulty or dirty injector will usually not pump in fuel properly. So instead of entering the chamber as mist, it goes inside as droplets, hence not burning completely. This unburnt fuel then passes through the piston, washing off the oil and diluting it.

Faulty carburetors

Old cars use carburetors to pump fuel into the combustion chamber. When the carburetor gets faulty or improperly adjusted, it can pump excess fuel into the intake system, which doesn’t get burnt during combustion. Consequently, the unburnt fuel may force its way through the piston rings and eventually ends up in the oil pan.

Leaky or faulty pumps

Old carbureted cars use mechanical pumps mounted on engine blocks or timing chain covers and driven by a camshaft to inject fuel into the combustion chamber.

When the diaphragm of these pumps gets faulty, they pump out too much fuel, which eventually gets past the piston and ends in your oil pan. And in some cases, they will internally leak out fuel directly into the crankcase instead of the weep hole, filling the oil pan with gasoline.

Misfiring cylinders

Misfires occur when the air-fuel mixture in the combustion chamber doesn’t ignite properly— ultimately disrupting the combustion cycle. How?

The inability of the air-fuel mixture to ignite usually causes the gas to wash down the cylinder walls, lowers compression and causes unburned gas makes its way to the piston. From the piston, it eventually enters the oil pan, causing a gas oil mixture.

Faulty piston rings

The piston rings seal the combustion chamber so gas does not escape during an explosion. If, however, the rings get worn out, they won’t be able to seal the combustion chamber properly, eventually letting gas into the crankcase.

Faulty mass airflow sensors

The mass airflow sensors help calculate airflow into the engine. This aids the engine in calculating how much fuel is also needed to achieve the proper air-fuel ratio. When the mass airflow gets faulty, it can force the ECU to think your engine is running lean.

Hence, causing the injectors to open widely and pump surplus fuel into the combustion chamber, which will not burn during combustion. This excess unburned fuel eventually gets past the piston rings and into the crankcase, filling the oil pan with gas.

Idling for too long, especially in cold climates

When you start your car and let it idle for long before driving, the fuel that sprays out condenses on the engine walls. And eventually, when heated up, it melts and seeps into the crankcase.

Too many short trips

Short drives never heat up the engine. Generally, gas runs into your oil pan at some point which won’t harm your engine, though in small quantities. So when your car heats up, the gas evaporates out of your oil.

If, however, you drive short distances, the oil will not heat up enough to evaporate the gas.  Should you continue for long this way, you would have a puddle of gas inside your oil pan.

oil stabilizer in gas tank

What causes oil in gas tank?

Oil mixes with gas, and gas can mix with oil. And we have stated above why you have gas in your engine oil. Let’s see how oil gets into your gas tank.

You accidentally poured oil into the gas

Some drivers have several look-alike gallons they use for storing gas and engine oil. So chances are they mistook the engine oil for gas and poured the content into the gas tank, thinking it was gas. This is why it is advisable to always mark the gallons with what goes in there. Or better still, use entirely different containers to store both fluids.

This also happens when using fuel treatments. People, in a bid to treat their fuel with fuel stabilizers, end up pouring oil stabilizers in gas tank. The only difference is most times, the gas dilutes the oil stabilizers, so it doesn’t really affect the engine.

For better engine performance

While some drivers use oil to top their gas to get to the nearest station, it’s a normal routine for others. These drivers intentionally pour oil into the gas tank for a better running engine.

For example, some people pour transmission oil in gas tank because it contains powerful detergents they believe will keep their engine clean.

Others have poured into the gas tank

Some persons, for reasons best known to them, can pour oil into your gas tank without your knowledge. The difference between you pouring it and others doing it is this. At least, if you made a mistake or did it intentionally, you would most likely put engine oil in gas.

But these weirdos can pour in just any oil. So don’t be surprised if you find baby oil or even cooking oil in gas tank. So if you’ve been asking, why is there oil in my gas tank? You may have created an enemy who is out to punish you by pouring oil into your gas tank

Some engine runs on mixed gas.

Before the introduction of 4-cycle engines, many old cars used 2-cycle engines. 2-cycle engines generally do not have an internal oil reservoir. So both the oil and gas go into the gas tank.

These engine types typically use the 2-cycle fuel, a mixture of natural fuel and 2-cycle engine oil. So for these engines, it is ok to have 2 cycle engine oil in a car gas tank. It’s important to note that these engines have been phased out in the United States since the 1960s.

How can you tell if gas has oil in it?

Virtually any oil can end up in your gas tank. If you’ve not accidentally poured it in, a weirdo can do this. So don’t be surprised if there is even cooking oil in gas tank chainsaw. But how can you tell you have oil in your gas tank, especially if you had no idea or can’t remember how it got there.

Check your gasoline color.

The fastest way to know if you have mixed your gas with oil is the color of your gas, especially if you’re unsure whether you added oil or not.  Gasoline is a transparent liquid, whereas oil comes in different colors. They could be blue, green, or red, depending on the oil you use.

Usually, a mixed gas will have a darker shade than the usual fuel. For clearer visibility, pour some of the mixed gas into a white container and check (avoid colored containers). If the gasoline has a certain color, unlike the fuel you know, you may have probably mixed the gas with oil.

Does your gas have the color of your lubricant? If yes, your gas has oil in it. However, we will understand if you can’t decipher it, especially if you’re not the one that added the oil. In this case, try the following tricks.


Undiluted gasoline has its unique smell, which you may be familiar with already. Usually, fresh gasoline has a sharp smell and should hit your olfactory sense sharply.  So if you don’t perceive this smell strongly, you probably may have mixed the gas with oil.

The paper test

If you can’t tell whether your gas has oil in it visually, try the paper test method. Get two brown paper bags. Pour pure gas into one bag and the oil-gas mixture you suspect into the other. Let both bags sit for a while and check.

The one with oil should leave oil residue on the bag after the gas has evaporated. Suppose this is the one in your gas tank; your car gas has oil. This method is a great way of detecting oil in gas, especially if you have other non- automobile oil such as baby oil in gas tank. This is true because such oil may not change the color or smell of the gas.

Viscosity test

Oil is usually thicker than fuel, and while oil will stick to your hand, fuel won’t. Here is what to do. Pour a small quantity of fresh oil into a container and your fresh fuel into another container. Observe how both of them feel on your hand.

Now, pour the suspected oil-gas mixture into a container and dip your thumb and index finger into it. Rub the fingers together to feel the texture of the said mixed fuel. Now compare the feel of the fresh oil, fresh gas, and the presumed mixed fuel. If the gas has oil, it will feel greasy and sticky in your hand.

Engine stalling

Another way to know you have engine oil in the gas tank is engine stalling. However, it depends on the amount. If the oil in the gas tank is small, it may not affect performance much. In fact, it will burn off after some drives. However, if there is too much oil, your engine will stall and eventually die.

Blue smoke

The emission of blue smoke from your tailpipe is one of the very common oil in gas tank symptoms. Except you’re using a 2-cycled (otherwise called 2-stroke) engine, oil shouldn’t be in your gas tank, especially in high quantities.

If, however, a high amount of oil finds its way into the gas tank, the fuel delivery system will supply the oil-gas mixture to the combustion chamber. During combustion, the oil gets burned.

The burned oil eventually leaves the engine not as the normal white smoke but as a cloud of blue smoke. The kind of smoke that can get you a ticket. This is usually evident in diesel engines. So if your diesel engine emits blue smoke, you may have engine oil in diesel fuel tank.

How do you clean out oil from a gas tank?

In many cases, it takes getting rid of the fuel in the fuel tank to clean out oil. Here is how to clean a gas tank.

Method 1:

Take out the gas tank from your vehicle. This can be a tedious job, but you can do it if you have the right tools and knowledge. Next is to drain out all the fuel. You will still have some oil in the tank; pour little fuel into the gas tank, swirl and pour it out again.

This should help remove the leftover oil. Maybe, it is also time to degrease the tank if you still smell gasoline. Afterward, reinstall the gas tank and add new gasoline.

Removing the fuel tank makes the chances of every build-up leaving the tank high. This method can be applied to virtually all automobiles. So whether there is oil in gas tank of your motorcycle, mower, or even diesel fuel tank, you can surely get rid of all the oil in the fuel tank.

Method 2:

 If you can’t remove the gas tank, you can still do it without removing the tank. Drain the fuel out through the drain plug if you have one. No drain plug? Relax; not having a drain plug on the gas tank is not a problem.

Shove in a hose into the tank and drain out as much fuel as you can, and then fill with gasoline. This method is ideal for small vehicles whose tanks are easily accessible. So if you have oil in gas tank lawn mower, you can try this out.

Note that oil will still be left in the tank but don’t worry. If the oil quantity isn’t much, it will eventually burn out as you drive. Yes! The car may be sluggish or smoke for some time, but eventually will be okay. If the car doesn’t start, pour little fuel into the carburetor or throttle body.

Method 3:

If you don’t know your way around, you have too much oil in your fuel tank, you’ve driven the car, and removing it seems hard, do not panic. Have your car towed to a facility that can drain out the mixed gas, especially if there is a lot of oil in the gas tank. In fact, this job is better left for gearheads.

They will drain the fuel lines, and clean the filters, spark plugs, and other components that the oil may have contaminated. This is to ensure oil is totally eliminated from the fuel tank and fuel delivery system.

How much does it cost to drain a gas tank?

Draining a gas tank lurks between $200-$500 depending on the amount of gas in the tank and whether the tank will be dropped. If the mixed gas has entered the fuel lines and engine, this job could climb as high as $1000-$1500.


Q: What does it mean when gas is in oil?

Gas in oil means that your car’s gasoline has found its way into your crankcase and mixed the oil in the oil pan.

Q: Does oil float on gasoline?

Oil does not float on gasoline. Instead, it mixes up with gas forming a solution that cannot be separated. This is true because gas is miscible.

Q: Will oil in gas harm the engine?

Except you’re using a 2-cycled engine, oil in gas will harm your engine. For regular engines, your oil is not supposed to be in the same place as gas. Oil in gas can cause stalling, emission of blue smoke, and even coat your catalytic converter since it’s not built to handle oil residue.

Q: Does oil mix with gasoline?

Generally, oil is not supposed to mix with gasoline. The oil and gasoline compartments are different since both have different functions.  If you realize that your oil has mixed with gasoline, something is wrong. That will leave you wondering how and why is there oil in my gas tank.

You may have accidentally poured in oil, thinking it was gasoline, especially if the containers look alike. Another reason could be that some jokers had poured oil into your gas tank without your knowledge in a bid to punish you. Or you’re using the 2-cycle engine that runs on 2-cycle fuel—a mixture of gas and 2-cycle engine oil.

What to Do for Oil in Gas Tank?

Having oil in gas tank is not uncommon for drivers. Some can accidentally pour it in, and in other cases, it is poured in by others. Either way, the most important thing is getting the oil out of the fuel system since this can ruin your engine.

While dropping the tank effectively removes the oil, one can still drain the contaminated oil without dropping it.

So which method to apply depends on you. People, who intentionally poured in the oil to make their engine run better, may not bother doing it. A good example is drivers using transmission oil in a gas tank to keep their engines clean since it contains powerful detergents.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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