Why Your Oil Smells Like Gas and How to Fix It?

Why Your Oil Smells Like Gas and How to Fix It

Have you ever popped open the hood of your car to check the oil and been hit with the overpowering smell of gasoline? If so, you’re definitely not alone. An oil that reeks of fuel is a common issue plaguing drivers, and is always a cause for concern.

But why exactly does oil smell like gas, and what should you do about it? Keep on reading, we’ll get to the bottom of this stinky problem.

Finding out that your motor oil smells like a full tank of unleaded is worrying for good reason – it’s often a sign of a more serious mechanical issue brewing under the hood.

Gas-contaminated oil can lead to reduced lubrication, accelerated wear, and serious internal engine damage if left unchecked. So getting to the root cause and fixing it promptly is critical.

We’ll cover all the key questions:

  • What causes motor oil to smell like gas in the first place?
  • How can you pinpoint exactly where the gasoline is coming from?
  • What are the most common repairs to eliminate that pungent gasoline odor for good?
  • And how can you help prevent gas from polluting your oil in the future?

Let’s dive in and demystify why your oil smells like a fuel pump.

What Makes Oil Smell Like Gasoline?

Before we get into diagnosing and fixing the problem, it’s helpful to understand why gas ends up mixing with oil in the first place.

There are a few common ways it can happen:

Faulty PCV System

One of the most frequent culprits is a glitch in the PCV or positive crankcase ventilation system. This system is designed to vacuum up the blow-by gases and vapor that accumulate inside the crankcase and recirculate them back through the intake to be burned off in the combustion chambers.

But if the PCV valves or hoses get clogged up with sludge and debris over time, they can’t do their job properly. Pressure builds up inside the crankcase, and these excess vapors get forced past worn seals and into the oil passages, tainting the oil with their fuel-like aromas.

Worn Valve Guide Seals

The valve guide seals are little rubber grommets that surround the valve stems, keeping oil from dripping down into the combustion chamber when the valves open and close. But these seals get baked by high engine temperatures and eventually shrink and harden over time. Once the seals become brittle and cracked, oil is able to seep past them and make its way into the cylinders.

And where there’s cylinders, there’s combustion. This leads the oil to get partially burnt and contaminated with the smell of gasoline fumes. Leaky valve guide seals are a very common source of oil that reeks of fuel.

Damaged Piston Rings

The rings that wrap around each piston are crucial for sealing in the combustion process and preventing oil from getting into the burning chamber. But these rings can get worn down or stuck in their grooves over years of driving, breaking their tight seal against the cylinder walls.

When the integrity of the piston rings becomes compromised, oil is able to leak past into the combustion area where it mixes with fuel and gets burnt. Once the contaminated oil makes its way back down into the crankcase, it brings that distinct gasoline smell with it.

Running Too Rich

Sometimes there’s nothing wrong mechanically – the engine is just getting fed too much fuel. A rich fuel mixture means there’s excess gasoline that doesn’t get fully combusted in the cylinders.

The unburnt fuel droplets eventually wash past the piston rings into the crankcase, polluting the oil with the stench of gas fumes in the process.

Diagnosing Why Your Oil Smells Like Gas

Finding out exactly why your engine oil reeks of fuel will take some diagnostic work to pinpoint where it’s coming from. Here are the main troubleshooting steps:

Look for External Leaks Near the Engine

One possibility is that gas isn’t making its way internally into the oil, but leaking externally from somewhere in the fuel system. Take time to inspect all the fuel components mounted on and around the engine.

Check for any pools of fresh gasoline or residue around:

  • Fuel injectors
  • Fuel pressure regulator
  • Fuel rails
  • Evaporative emissions (EVAP) canister and hoses
  • Intake manifold

Don’t neglect to examine the valve covers either. Fuel-contaminated oil can sometimes leak externally past worn gaskets and seals.

Hopefully it’s just an accessible external leak that can be readily fixed.

Scan for Trouble Codes

Connecting a diagnostic scan tool and pulling the on-board diagnostic (OBD2) trouble codes is an easy first step. Check to see if any engine-related or evaporative emissions codes have been set that could provide helpful clues.

Check the PCV System

As discussed earlier, a clogged PCV system is a prime suspect for oil that reeks of gasoline. Inspect the PCV components:

  • PCV valve – Remove it and shake it, it should rattle freely. If not, it’s clogged. Inspect the exterior for a thick, oily coating. Clean or replace it.
  • Breather hoses – Ensure they’re connected properly with no cracks or blockages.
  • Oil fill cap – Make sure it’s not clogged, preventing ventilation inside the engine. Remove it while idling – the motor should not sputter or stall.
  • Check valves – Vacuum leaks here can indicate a problem. Spray cleaner around them and listen for changes in idle speed.

Overall, if the PCV system is original or high mileage, it’s smart to just replace the whole thing.

Do a Compression Test

A compression test can reveal insightful clues. It determines if the cylinders are able to hold adequate combustion pressure, or if compression is leaking past worn piston rings or valve seals.

After warm up, test each cylinder in succession. Healthy readings should all register within 10-15% of each other. Dramatically lower numbers indicate where compression is escaping. This points to worn rings or bad valve seals on those cylinders allowing gas and oil to commingle.

Monitor Short and Long Term Fuel Trims

If you or a shop have access to a professional scan tool that can view live engine data, keep an eye on the short and long term fuel trim levels. This monitors how much the engine computer is adjusting the air/fuel ratio.

Higher positive values indicate the engine is running rich, meaning there’s unburnt gasoline washing past seals into the oil.

Perform an Oil Consumption Test

This involves regularly checking the oil level under the exact same conditions over a span of 1000-2000 miles. High oil consumption points to fuel contamination problems.

The compression test and fuel trim data will give you most of the needed diagnostic information. But an oil consumption test confirms if the engine is actually burning off and using up abnormally high oil.

Common Repairs to Eliminate Oil Smelling Like Gas

Once the root cause is uncovered, here are some typical repairs to address that pungent gasoline smell coming from your engine oil:

Fix EVAP or Fuel System Leaks

If you located any external leaks from cracked hoses, bad seals, or damaged components near the engine, address those promptly. Tightening connections, replacing worn parts, and re-sealing or replacing gaskets will take care of external leaks.

Replace PCV Valve and Hoses

As outlined earlier, installing a fresh PCV valve, breather hoses, and cleaning the related passages is critical to keep the crankcase properly ventilated so blow-by fumes don’t contaminate the oil.

Replace Valve Guide Seals

Leaky guide seals are a very prevalent problem leading to that characteristic fuel smell in oil. Replacing all the valve guide seals involves a significant teardown known as a cylinder head job. This isn’t cheap, but it’s the only remedy if they are worn.

Engine Overhaul for Piston Rings

When the piston rings have worn and are allowing gas to leak into the crankcase, the only repair is an engine overhaul to install new piston rings. This gets very costly for sure, so weigh the costs versus just getting a remanufactured engine.

Adjust Fuel Mixture

If the engine is just running rich and dumping raw fuel into the cylinders, adjusting the air/fuel mixture should help. A mechanic can tweak the mixture and replace any faulty fuel injectors. This may cure oil smelling like gas without major repairs.

Proper repairs come down to determining if the source is external leaks, ventilation issues, or internal wear. While repairs can be pricey for worn parts, addressing the problem promptly saves your engine from severe damage.

How to Help Prevent Gas in Your Oil?

No one wants the headache and expense of fixing contaminated oil. So what preventative maintenance can minimize oil taking on that gasoline smell down the road?

Regular Oil Changes

Diligently changing your oil every 5,000-7,500 miles with quality synthetic oil helps remove fuel residues before they accumulate at higher concentrations.

PCV System Maintenance

Inspecting the PCV valve, hoses, and related components periodically for clogging, and replacing them every 50k miles or so keeps blow-by gases venting properly.

Watch Oil Consumption

Keep an eye on oil use between changes – burning more than a quart every 1,000 miles warrants investigation for fuel contamination.

Don’t Ignore Oil Leaks

Promptly repairing any leaks from gaskets, seals, and worn rings reduces chances of gases escaping into the lubrication system.

Tune-Ups and Engine Service

Good engine tune up practices like replacing spark plugs, fuel filters, O2 sensors, cleaning the EGR, and servicing injectors assures your engine isn’t running too rich.

While a faint gasoline smell in your oil may come and go, constant fuel odors point to an underlying leak or wear issue that demands attention to avoid harming your engine. Investigating where it’s coming from and making necessary repairs provides peace of mind against steep repair bills.

Does your car have oil that reeks no matter what you try? Feel free to bring it by our shop – our techs have tons of experience tracking down and fixing the source of that pesky gasoline smell in oil. We’ll have your engine smelling fresh again!


So there you have it – whether it’s worn piston rings, leaky seals and gaskets, or PCV issues, contaminated oil that smells like gas is never normal and risks damaging your engine’s health. Finding and fixing the cause of the leak, ventilation problem or excessive fuel entering the chambers is key to not just eliminating the noxious odor, but also preventing premature wear and failure in your car’s motor. With some diligent diagnosis and the right repairs, that sweet scent of fresh oil will return!

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