In the process of changing or checking your oil, you may have noticed a distinct gas smell coming from your car’s oil.  There are a few reasons why gas may have made it into your oil and a few reasons why it’s bad. Suffice to say though, if there’s enough gas in your oil for you to smell it while changing or especially checking your oil, it’s reached the point where it could be considered a serious problem.

Why Is It Bad?

First off, your oil smelling like gas means that there’s probably something going wrong with your engine. So even if it weren’t a problem in itself (it is) it means you need to check for other issues with your engine. Beyond that though, there are two main reasons why having gas in your oil is a bad thing.

The first is fuel economy. If your fuel is leaking into your oil, it’s being heated and vaporized rather than burned by your engine. That means that some portion of the money you spend filling up your tank is literally vanishing into thin air. The extent to which that’s the case depends on how much is leaking into your oil, but it’s not a good thing regardless.

The second issue is far more serious. If the composition of your oil changes too drastically, in this case thinning out too much because of the gasoline, it’s not going to correctly lubricate your engine. That means greater wear and tear, and the increased likelihood of expensive breakdowns. It’s not likely to cause an immediate issue (unless the issue causing it is severe enough) but if left unattended could require expensive repairs and replacements down the line.

Related: Lifespan Of Gasoline And How To Store It Properly

What’s Causing It?

There are a few causes, some more severe or easier to fix than others. They include:

Worn or Damaged Piston Rings

The piston rings in your car serve several purposes, but the main ones involve regulating oil pressure and application. If they’re worn down or become damaged in some way, it could be allowing fuel to get into your oil pan causing the gas smell you’ve noticed. If your oil needs to be changed more frequently, and your car is giving off excessive (but still grey/white) exhaust smoke, that combined with the smell of gas likely signals a piston ring issue.

Combustion Chamber Issues

If your oil smells like gas, it could also be an issue with your combustion chamber not igniting correctly. Things like engine knocking or other issues caused by heat or engine pressure not being correctly regulated can cause fuel to leak into your oil pan and cause the smell. If you noticed irregularities in your engine performance, including an occasional pinging sound, that along with the smell of gas likely means there are issues with the combustion chamber.

Spark Plugs

Similar to the above, misfires, most commonly caused by a faulty spark plug, can cause combustion chamber issues. While it’s also technically a combustion chamber issue, it’s one that’s far more common, and can be checked and repaired more easily, so it deserves its own spot on the list.

Faulty Sensor(s)

A faulty sensor could be causing your fuel to be too rich and is another reason your oil may smell like gas. Fuel being too rich means that there’s too much fuel and not enough air being injected into the combustion chamber. Most commonly, this is going to be caused by one of the several sensors that control this not working correctly. The mass air-flow sensor, coolant temperature sensor, O2 sensor, MAP sensor, and the intake air temperature sensor all play a role in regulating the air-fuel mixture that gets injected into your engine.

If any of them are not functioning correctly it could cause your fuel to be too rich, which means it won’t burn correctly and could be getting into your oil. If you’ve noticed black exhaust smoke that smells strongly of gas, along with the gas smell in your oil, it’s probably the fuel mixture, which is most commonly caused by a faulty sensor.

Faulty Carburetor (Older Cars)

A faulty carburetor can also cause your fuel mixture to be too rich, resulting in more or less the same symptoms as above. The difference, of course, is that this is a mechanical issue caused by the engine part the delivers the fuel portion of the air-fuel mixture malfunctioning, rather than incorrect information being fed to the part.

Most commonly, the valve that lets air into the mixture can become stuck, which will cause the fuel mixture to be too rich, meaning gas can be forced past the piston rings into your oil, which causes the smell. If this is the issue, you’ll likely notice the same black, smelly exhaust as you would with the sensors malfunctioning. You may also notice frequent backfiring or misfiring, and difficulty starting the vehicle, in addition to the gas smell.

Faulty Fuel Injector (Newer Cars)

In newer cars (newer here being any car made after 1995) you have a fuel injector rather than a carburetor. The fuel injector is theoretically a more precise instrument, but they can still have issues that will cause excess fuel to leak out and into your oil. If they’re dirty or clogged (the most common problems) or have broken or malfunctioned in other ways, you may notice other issues in addition to your oil smelling like gas. The car idling roughly, your RPMs spiking or dropping are common symptoms a faulty fuel injector.

Frequent, Short Trips

Let’s end this list on a high note. If you’re driving your car regularly, but only ever for short distances (say, less than 3 miles), the smell of gas in your oil might not mean anything is wrong whatsoever. Here’s why.

Even if your car is functioning normally, small quantities of gas are always going to make their way into your oil. It’s not uncommon for your oil to have a tiny percentage of gas mixed in with it, you just don’t smell it because there’s not enough to smell. As your car heats up over extended use, so does the oil, and the gas inside to converts to vapor and dissipates naturally. However, if you’re only driving short distances, your oil never heats up enough to evaporate all the gas, causing it to build up, and creating the gas smell you’ve noticed.

That buildup however means that the oil is going to reach a point where it’s not operating at its most effective oil. If you drive exclusively short distances, you should be changing your oil more frequently, or at the very least, checking it frequently and changing it once you notice that buildup occurring.

Rich Fuel-Air mixture. 

The formation of a mixture that is too rich can be caused by various reasons. Gasoline in such a mixture is not completely burned, its residues condense on the walls of the cylinders, and from there get into the crankcase, mixing with the fuel oil of the combustion engine.

Air-Fuel Ratio

In Conclusion

If your oil smells like gas, don’t panic, at least not immediately. If it’s a major problem with your engine, there are likely other symptoms along with the smell of gas. That means it’s extremely unlikely that the smell of gas is going to be your first and last warning of a pending catastrophic engine failure. It’s still something you should take seriously, especially if it persists across multiple oil changes.