If you check your dipstick to determine if your vehicle is burning oil and the fluid on it looks too thin or smells like gasoline, it’s important to figure out what’s going on. Gasoline isn’t supposed to end up in your oil system. Your oil lubricates the moving parts inside the engine. It’s thicker than gasoline and formulated specifically to withstand heat when the engine is running at high speeds for long periods.
An automobile engine has three fluid systems that support proper function but should not intermingle. The systems are:
- Fuel, for propulsion.
- Oil, for lubrication of internal moving parts.
- Coolant, to keep the engine from overheating.
However, there are several ways that gasoline can get into oil. Some are nothing to worry about, while others are alarming and require immediate attention.
Experts say your vehicle is more likely to have fuel mixed in the oil if:
- Your driving is “in town” short trips with lots of stops and starts.
- Your driving involves a lot of cold starts.
- Your oil changes are infrequent.
Symptoms of Gas in Engine Oil
You may notice your oil is getting diluted with gasoline if your dipstick suddenly shows more oil in the system than it did the last time you checked (or the stick is showing an over-full crankcase). Some automakers are putting an extra line on the dipstick so that vehicle owners can easily see when the crankcase is over-filled. Whether by gasoline infiltration or too much oil in your car, an over-filled crankcase is not a good situation as it can push oil past the pistons and into the gasoline, among other problems.
Other signs that gas and oil are mixing in your engine include:
- Poor engine performance, including sluggish acceleration.
- Black smoke from the tailpipe.
- Unexplained stalling.
- Check the engine light on the dashboard.
- A sudden decline in gas mileage.
- Gasoline smell when you check the oil dipstick.
What Does Gas in Oil Look Like?
Fresh oil has a golden color to it, but it is mostly transparent. If gasoline gets into the oil, it’s much thinner and is likely to have very little color to it. When you look at your oil dipstick, gasoline in the oil can make the oil look more like water, and it will run off the stick quickly.
How Does Gas Get Into Oil?
- Blowby: The most common way for gasoline to get into oil is around the pistons that affect an engine’s combustion cycle. Pistons are meant to fit smoothly inside a valve, with the lubricating oil in the crankcase space below and the gasoline-fueled combustion happening in the space above. However, pistons don’t completely fill the valves, allowing the pressurized gasoline to sneak by and enter the crankcase oil. This is called blowby, and is generally not a problem because it’s a very small amount of fuel, and as the engine heats up, the gasoline burns off.
- Fuel Pressure Regulator: This device ensures the appropriate pressure for fuel moving from the tank to the fuel injectors and back to the tank. There are many parts within the regulator that can go bad or get jostled out of place, including small springs. If other tests do not show an obvious culprit for the gasoline getting in the oil, have the regulator checked. If the regulator has failed there will probably be other symptoms as well, such as poor gas mileage, rough idle, weak acceleration, and a check engine light illuminated on the dashboard.
- Leaking Fuel Injectors: If an injector is bad it will leak fuel, compromising the fuel pressure regulator’s job. Remove injectors and have them checked. If they smell like gasoline when removed, it’s likely they need replacement. When the injectors are removed, do a compression test to ensure that the engine is capable of holding an appropriate amount of pressure. If not, the engine will not fire as needed to run properly.
- Leaking Rings: Rings are the part of the piston that fits snugly inside the valve. Too much torque or wear can cause rings to become bent, allowing gasoline to flow by in larger than normal “blowby” quantities. Rings can be fixed, but it’s a big job.
The Role of Sensors in the Fuel System
Sensors are increasingly important components of modern car engines. These are small gauges that report to the onboard computer to maintain the proper settings for various engine functions. When sensors malfunction, you should get a warning light on your dashboard. Sensors that impact the flow of gasoline include:
- Fuel pressure sensor. This is part of the fuel injection system and is usually located on the bar with the fuel injectors. It ensures that the gasoline going to the injectors is calibrated accurately and that the fuel pressure regulator is working properly.
- O2 sensor. Located in several places, including near the catalytic converter and in the tailpipe, these oxygen sensors detect the presence of oxygen and can tell if the fuel-oxygen mixture in the engine is off. If there’s too much fuel flowing to the spark plugs, some may get pushed past the pistons and into the crankcase oil.
- Air intake sensor. These are located in the air intake on the top of the engine (not all vehicles have them). This sensor reads the air temperature to ensure the right mix of fuel and oxygen for the engine. Colder air is denser.
- Coolant temperature sensor. If you do a lot of short trips and your engine never gets hot, this sensor is more prone to failure. It tells the engine how much fuel to add to the combustion mixture (with oxygen). A cold engine needs more fuel, which can result in too much pressure on one side of the pistons if the sensor is failing.
- Fuel temperature sensor. This is located on the fuel pump, and further refines the process of fuel-oxygen delivery to the engine.
Is It Safe to Drive a Car If You Smell Gas in Your Engine Oil?
No, it's not safe because the gas thins out the oil, which means your engine won't be properly lubricated. This can lead to engine damage and should be fixed immediately.
What to Do If You Detect Gasoline In Your Oil
Get your oil changed. If you have someone else change your oil, ask if the amount of gasoline appears excessive. If the answer is not clear, pay close attention to your car’s performance and check the dipstick frequently over the next several weeks. You’re fortunate if you caught the issue early. If check engine lights come on, it’s time to take additional steps to isolate the problem.
Preventative Measures
Regular maintenance should prevent gas from getting into your oil through leaky valves and bad injectors, but older vehicles and your driving habits take a toll on a car’s engine. Discuss the situation with a qualified mechanic to explore ways to prevent further damage to the engine.
When to Seek Professional Help
If you’re not a mechanic with intimate knowledge of injectors and gaskets, it can be tough to tackle diagnosing and repairing a problem like this. You may be able to narrow down the potential sources of gasoline in your oil by researching the model of the car you have and inquiring in owner’s forums if it’s a common complaint. If you have a check engine light or an oil light illuminated on your dashboard, you may also buy or borrow an OBD tool to diagnose sensor codes, which may point more directly to the source of the problem.
The complexity of modern vehicles makes it difficult for an untrained person to be their own mechanic. There’s no shame in asking a mechanic to diagnose an issue – and it’s usually the best choice because they can make repairs before the issue further damages engine components.
A minor issue of blowby should clear up easily without further issues, but something more serious will become apparent in the way the car operates, whether your MPG drops or the driving performance declines.
If your dipstick shows that the oil level is apparently going up, or you smell gasoline when you check your oil, it’s worth looking more closely at ways gasoline is likely getting into the oil.
