Common Reasons Why Your Engine Oil Smells Like Gas

Engine oil typically has a mild smell akin to plastic if you can smell it at all. So, when you open the oil fill cap and smell something different, something might have gone wrong with the oil or the engine. But what happens if the oil smells like gas?

Here’s Why the Oil Smells Like Gas

Some of the reasons why oil smells like gas are benign. Unfortunately, most have an associated problem that you must fix to remove the smell and prevent things from taking a turn for the worst.

Here are the common reasons why your car’s engine oil smells like gas:

Piston Ring Blow-By

In many cases, piston ring blow-by is the culprit for why oil smells like gas. Blow-by refers to the event where air-fuel mixture or exhaust gasses escape the engine past the piston rings and gaps in the cylinder walls.

There are always some blowby. The seal of metal on metal isn’t perfect, and there’s a tiny gap at the ends of each piston ring. Remember: the air/fuel mixture is being compressed for nearly the entire compression stroke before the spark occurs.

The blowby gasses and a small amount of unburned fuel mix with the engine oil, giving the lubricant the distinct smell of gas.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: If you pull the dipstick and let a drop of engine oil drip on a clean paper towel, watch for a thin liquid to weep out of the oil droplet into the surrounding paper. Moisture or gas will weep out of a drop of oil this way. Regular oil changes will mitigate oil contamination.

Faulty Piston Rings Will Cause Excessive Blowby

Piston rings are parts that seal the combustion chamber. The rings minimize the amount of gas that escapes to the crankcase. While there will always be some blowby, worn piston rings will cause excessive blowby.

Fuel Injection System Leaks or EVAP system issues.

Does your vehicle have a fuel injection system? One of its parts might have developed a fuel leak, leading to gasoline eventually reaching the crankcase or oil pan.

The fuel injection system has various parts that work together to deliver the correct amount of fuel to the engine. These parts include fuel injectors, fuel pressure regulators, and fuel lines.

Fuel injectors can fail so that they drip fuel into the cylinder when the engine is shut down. Fuel pressure regulators have a vacuum diaphragm that can fail and allow fuel to pass through the regulator vacuum line into the manifold.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: On the EVAP system, a saturated carbon canister due to packing the fuel tank can cause unexpected fuel contamination, enriching the mixture and adding to the normal blowby of fuel into the crankcase.

Incomplete Combustion

Incomplete combustion is inevitable during cold starts. When you fire up a cold engine, it usually runs on a rich air-fuel mixture to help it get going. Not all the gasoline gets burned, and some gas can wind up in the crankcase via natural blow-by. Any engine that is started cold and moved a very short distance several times in a day every day will always need more frequent oil changes than a highway vehicle.

Likewise, driving your vehicle for brief periods or over short distances so that it doesn’t warm up completely before turning off the engine will also leave some fuel unburned. During quick drives, the engine can’t gain enough heat to evaporate fuel in the crankcase and process it with the PCV system; not to mention, the moisture that isn’t processed as well by the PCV on a cold running engine.

A failed open or removed thermostat can cause the same problem. The engine should run just over 200 degrees to remain healthy.

Engine Misfires

When the ignition system fails to ignite the air-fuel mix correctly, it can cause a misfire. Engine misfires are serious problems, but one of their possible side effects is making engine oil smell like gas.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: That being said, most PCM/ECM algorithms since 1994 will stop firing the injector on a misfiring cylinder to prevent catalyst damage.

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An engine misfire can spread gasoline across the cylinder, degrading the protective layer of oil that coats the walls. This cylinder wash lowers compression, leading to more engine blow-bys through the piston rings.

Accidentally Filled the Oil Pan With Gasoline

If you’re a rookie driver, you might have accidentally put gasoline in the oil pan instead of engine oil. Always store the containers in the right location and check labels to prevent misuse. You don’t ever need to open the hood to fill the fuel tank unless you’re driving a mid-60s Volkswagen Beetle.

Oil Change Schedule

When was the last time you replaced your car’s engine oil? If your last oil change feels like a faint memory, that’s long enough for gasoline to seep into the oil pan.

While the engine might not have a major leak, minuscule amounts of gasoline still get out. That gas enters the oil pan and accumulates. If you don’t perform oil changes regularly, the oil will have enough gas to smell differently.

Engine Oil Smell

Some engine oil products smell like gas. Several drivers who use the Mobil 1 FS X2 5W-40 product have shared that the oil will start smelling like gas if you leave it out in the bottle.

Reasons to Stop Driving When Engine Oil Smells Like Gas

Now you know why your car’s engine oil smells like gas. But why should you be concerned?

Diluted Engine Oil

Gasoline dilutes oil, degrading the lubricant’s ability to absorb heat and reduce friction for the moving parts that the grease coats. The engine has a higher chance of overheating, and its internal components might wear out faster without the protection provided by the engine oil.

Engine Issues

Furthermore, gasoline contamination of engine oil can lead to engine issues. Possible outcomes include knocking, misfiring, and complete engine failure.

Luckily, it generally takes time for the more severe issues to happen. Before things get worse, check your vehicle to find what’s behind the engine oil that smells like gas.

Where to Shop for OE-Grade Engine Parts for Your Vehicle

Sometimes, you can do everything right for your vehicle, and it still won’t run the same way. Engine troubles are indeed a handful to deal with, mainly because it’s hard to pinpoint which parts need to be replaced at first glance. But whether you’re in need of new pistons, cranks, fuel system parts, or a whole new engine assembly, you can rest assured that CarParts.com has exactly what you need.

Sourced from only the most trusted aftermarket brands, our high-quality engine parts are guaranteed to get your vehicle running like it’s as good as new. Choose from only the most trusted manufacturers today, and enjoy a personalized shopping experience when you buy from us.

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