If your car’s oil smells like gasoline, you have a problem. So, if you’re checking your oil and the oil dipstick smells like gas, don’t waste time further diagnosing the source of the issue.
Understanding what the problem could be will help you figure out if your car needs immediate repairs or if you can limp along a bit before working on it yourself or finding a mechanic.
But half the stuff you read on the internet is trying to sell you something, so it’s hard to tell what is fact and what is a sales gimmick.
Don’t worry. Keep reading, and you’ll have the answer to why your car’s oil smells like gas, and maybe more importantly, what to do about it.
What Happens When I Run My Gasoline Engine?
Automobile engines that use gasoline as a fuel have a series of cylinders. Different cars with different engines have different numbers of cylinders. For instance, a new Chevy Tahoe might have an 8-cylinder motor, whereas a BMW M4 has a six-cylinder motor.
The number of cylinders doesn’t matter when you’re trying to find the source of gas in your oil. But it’s good to understand the basics of how an internal combustion motor fueled with gasoline works, so you can more effectively trace the source of your gasoline entering the oil.
Fuel (gasoline) and air mix together inside of each engine cylinder, supplied by the fuel system and the air intake system. Then, a spark ignites the two, causing combustion and driving the cylinder’s piston. The more fuel, air, and spark you introduce, the faster the combustion reaction moves the pistons up and down.
That combustion reaction is extremely powerful, and it creates energy that in turn powers your car’s wheels, propelling you down the road. The pistons of an engine cycle very fast, and in order to keep the fuel, air, and combustion byproducts well-contained and separate from the rest of the engine, each piston has a ring around it.
As your motor’s pistons turn many thousands of times, it experiences extreme temperatures and friction. Oil lubricates the cylinders and moving parts, keeping them moving freely and preventing overheating from friction.
To get an idea of how hot things can get, check out this video of a Cosworth engine from a Formula 1 race car. The exhaust glows red hot!
But when things start to go wrong, there are places where gasoline can find its way into the oil, reducing efficiency and potentially leading to catastrophic failure of the engine. Keeping an eye (and a nose) out for issues can help you find a problem before it leads to breakdowns and damage.
What Makes Oil Smell Like Gas?
Now that we have a bit of a baseline understanding of how an engine works, we can discuss what’s happening if your oil smells like gas. Since we know gasoline and oil aren’t supposed to mix, there are a few likely places where you’ll need to check for issues.
Gas Leaking From a Fuel Pump
Depending on what kind of car you have, your engine may have a fuel pump or rail system right nearby or even on top. It’s possible that the pump itself, or one of the lines running to or from it, is leaking.
This can allow fuel to drip or seep right onto your motor and put off an odor of gasoline when you’re driving, looking under the hood, or checking your oil.
Look carefully for any signs of seepage, dripping, or discoloration on the engine or in the engine bay. Address any obvious leaks immediately, as gasoline is flammable, and having it drip on a hot engine or exhaust could cause a fire.
The Engine Oil is Running Rich
When an engine isn’t getting enough fuel to run correctly, it’s said to be running lean. On the flip side of that coin, an engine that’s running rich is getting too much gasoline.
Computers control the fuel mixture on most modern cars, regulating the ratio of fuel to air to ensure complete detonation of the mixture and efficient engine operation. If there is a problem with the computer, the ratio may not be correct, leading to leftover fuel sitting in the cylinder.
When undetonated fuel is left in the cylinder, it tends to seep past the rings and seals, making its way into the oil.
Consider checking a few things to make sure your engine fuel mixture is correct.
- Clean your air filter and remove any debris from your intake. If your car isn’t getting enough air, it may lead to the engine running rich.
- Use the manufacturer’s recommended octane. If you’re running very high-octane gasoline in an engine designed to run something less potent, you can end up with undetonated fuel.
Faulty Fuel Injector
When it comes to the air-fuel mixture, fuel injectors are a major player. The fuel injectors deliver the appropriate amount of fuel-air mixture to the cylinder walls at exactly the right temperature. Your car’s computer controls a built-in solenoid in the fuel injectors, which provides a small pulse of electricity to the injectors and opens them briefly. When this happens, fuel is released into the intake manifold and cylinder.
If your fuel injector clogs, over time it may fail to adequately supply the engine with fuel. Without enough gasoline, your motor can end up running rich or lean. This will affect not only how it runs, but also its smell. A faulty injector may also let a small amount of gas seep into the oil through a crack or other defect. Replacing an injector can be time consuming, so it’s important to find out what the root of the problem is before diving too deep into your engine.
Faulty Piston Rings
When pistons move up and down in the combustion chamber, they leave some amount of gas behind each time. The piston rings are there to seal off the cylinder and keep it from leaking on either side of the piston. They do this by getting squeezed between the top of the cylinder head on one end and oil or other types of cylinder goo on the other end. When they don’t work properly, they can let some amount of gasoline seep past them into your cylinders—which can make its way into your oil pan.
You Drive Short Distances Too Frequently
When you only drive short distances, the engine won’t get up to a very high temperature. If you have a minor problem with trace amounts of gasoline contaminating your oil, the engine won’t get hot enough to vaporize the fuel.
That means that you may smell gas in your oil. To be clear, if you get an occasional whiff of fuel while checking your oil, that’s one thing. If you get a tremendous amount of gasoline smell while driving, you should stop immediately and have your car towed to a mechanic.
But if you’re always taking short trips, and you smell a trace of fuel in your oil, try taking a long trip and getting the engine hot enough to cook off minor gasoline accumulation in the oil.
Other Ways Gas Got Into Your Oil
There are a few other less common ways for gas to get into your oil.
- The piston rings have become worn or unseated
- Accidentally used gas to top-off oil
- Accidentally used a fuel blend with oil (for two-cycle engines)
How to Further Diagnose the Source of Oil in Your Gas
Not everything requires a trip to the mechanic. Even if you don’t intend to perform a repair yourself, there are some things you can do without much experience to troubleshoot the source of why your oil smells like gas.
By doing so, you might reveal a simple issue you can fix yourself or even save yourself lots of money on expensive diagnostic fees.
Run a Diagnostic on Your Car at Home
Many cars have a port where a diagnostic computer can access the computer and scan for error codes. A simple code reader is usually pretty inexpensive. And, after plugging one into your car, it can instantly reveal ‘trouble’ codes that may indicate the source of the oil in your gas.
Some codes include:
- Cylinder misfires (It will even tell you which cylinder to help you diagnose the issue further)
- An overly lean or rich fuel mixture
- Oxygen sensor failure (May affect the mixing ratio of fuel and air)
- Fuel mixing ratio issues caused by equipment failure (Could indicate an issue with the fuel, its pump, or the airflow)
- Exhaust gas issues (May indicate the need to take some longer trips)
- Loss of compression (Could indicate piston ring failure)
What About Older Cars Without Computers or Fuel Injection?
Older cars that don’t have computers or fuel injectors still run on the same combustion principles. But instead of looking at a computer screen to diagnose problems with gasoline in your car’s oil, you’ll have to look for physical signs:
- Check your spark plugs for signs of wear or blackening, indicating failure or a rich mixture
- Adjust your carburetor to get the correct fuel mixture
Other Associated Issues
Look out for a few signs of other issues with your car that may also indicate the need for repairs. When you smell gas in your oil and see one of these other symptoms, you may need urgent repairs to head off doing more damage to your vehicle:
- Strong smell of gasoline while driving or parked
- White, grey, or black smoke coming out of your exhaust pipe
- Iridescent streaks on your engine’s oil dipstick
- A significant increase in oil level without adding any
- Poor fuel economy
Tips for Finding the Source of a Leak
If you suspect something is dripping from your car, but you can’t figure out what it is or where it’s coming from, you can try a couple of tricks:
- Tape off electrical connections and carefully clean your engine bay to remove stains and grease deposits. Here’s a good demonstration of how to get things looking fresh and clean. Then, run your engine with the hood up and watch for stains, drips, or seepage to appear.
- After parking your car, slide a piece of cardboard on the ground underneath the engine area. Leave it for a few hours or overnight. In the morning, take note of any drips or stains on the cardboard. Lay down and look for leaks in the motor area that was above the stain on your cardboard. You might even be able to tell from the stains on the cardboard what exactly is dripping.
What Could Happen If My Oil Smells Like Gas?
If you don’t do anything to address your oil smelling like gas, a range of things can happen. If you’re only building up trace amounts of fuel in your oil due to taking short trips, you can address that is a minor issue by driving more.
You might even want to change your oil first and see if the smell of gasoline goes away.
But if you have a more significant issue, you run greater risks. Let’s look at a few, from minor to major.
Gasoline mixed in your oil will reduce the ability of your oil to coat and lubricate parts properly.
Your engine won’t run as efficiently as it should without maintaining the separation of oil and gas. Eventually, the oil may work its way back into your cylinders, creating a situation where your car’s exhaust is even more unfriendly to the environment.
Oil seals are not meant to stand up to the chemicals in fuel. They may wear at an accelerated rate if there is gasoline mixed with your oil. This can end up leaving you leaking oil, potentially running your engine if left untreated.
Gasoline is highly flammable. Even a tiny amount of liquid or vapor gasoline can fuel a fire. In 2018, the most recent year on record, the National Fire Protection Agency (NFPA) reported more than 200,000 vehicle fires that injured thousands and claimed more than 500 lives.
Don’t trifle with suspected gasoline leaks.
If your oil smells like gas, you should investigate the source promptly. It may not be a sign of a significant breakdown. But left untreated, it could accelerate the deterioration of your car or end up in catastrophe.
Try to find the source of the gas smell and if you smell a lot of gasoline in your oil and can’t fix it yourself, call in a qualified mechanic without delay.