Motorcycle Oil Smells like Gas? Here’s Why (For Beginners)

As fuel for motorcycle operation, gasoline is one of the more obvious critical components of a fully-functional motorcycle.

That said, engine oil is just as critical to the healthy functioning of a motorcycle as it provides proper lubrication and cooling to the motor, transmission, and gearbox components.

If your motorcycle engine oil smells like gas, it may be due to the fuel in your oil pan, which can cause engine overheating, gearbox failure, and acceleration of engine wear.

This article will list the primary reasons why motorcycle oil smells like gas and how to troubleshoot the problem. 

1. The Motorcycle is Riding Short Distances

Fuel and oil mix inside your motorcycle engine’s crankcase during routine operation.

While fuel has a low flash point (the temperature at which it ignites and combusts), motorcycle engine oil maintains its liquid lubricating properties even when exposed to high heat.

Therefore, when your motorcycle oil reaches its operating temperature, the fuel heats up and vaporizes, separating itself from the engine oil before it interferes with the engine cooling process.

If you typically only ride your motorcycle short distances without giving the oil a chance to heat up,  the small amount of fuel inside the oil point won’t get hot enough to vaporize.

If you don’t ride your long bike distances from time to time, more and more gasoline will integrate into the engine oil until your oil smells like gas.

Eventually, enough fuel content is in your bike’s oil supply to hurt its engine-lubrication properties.

Suppose you only ride your motorcycle short distances. In that case, your oil supply never reaches its ideal operating temperature, and the slight amount of fuel that’s entered your oil will remain.

Here’s what to do if you’re in this situation: 

• If you suspect this is why your motorcycle oil smells like gasoline, replace your engine oil and filter asap.
• Take at least one 30-45 minute ride a week to heat your oil. This will not only vaporize any fuel content but also thin the viscosity of your oil and pump it through your engine for proper cooling and lubrication.
• If you cannot ride your motorcycle for more than a short distance data time, changing your oil and filter at half the recommended intervals will prevent your motorcycle’s engine oil from smelling like fuel.

2. The Motorcycle Engine is Misfiring

An engine misfire is when the air: fuel ratio isn’t ignited at the appropriate time, hurting the whole combustion cycle.

If the fuel in your air-fuel ratio isn’t ignited properly, the unburned gas shoots down your engine cylinder walls.

Engine misfires can alter the internal engine compression enough to let the gasoline seep past the piston rings and down into your oil pan, causing your motorcycle engine oil to smell like gasoline. 

Engine misfires are most commonly caused by the following:

• Faulty Ignition Coil
• Faulty Spark Plug
• Leaking Intake Manifold/Broken Manifold Gasket
• Deficient Fuel Pressure
• Defective Fuel Injector
• Faulty ECU or Engine Sensors
• Inadequate Compression

3. The Fuel Injector is Failing

On a modern, fuel-injected motorcycle, an Electronic Computer Unit-governs a solenoid. This then operates a system of small fuel injector components, ensuring they each deliver the precise amount of fuel at the accurate time.

Some of the cheaper mechanical motorcycle solenoids are prone to early failure. Faulty solenoids can get stuck in the open position, allowing gasoline to flow freely at inappropriate times.

A faulty fuel injector can let an excessive amount of fuel into the engine at the wrong time so that it mixes with engine oil and seeps into your oil supply, causing your motorcycle’s oil reservoir to smell like fuel. 

Here are some common reasons why a fuel injector fails:

• Dirty or Carbon-Clogged Fuel Injectors
• A broken Injector O-Ring Causes Leaking
• Internal Part Wear-and-Tear
• Contaminated Fuel Supply/Poor Quality Fuel

4. The Carburator is Failing

Before electronic fuel injection became the standard,  motorcycles used a mechanical component called the carburetor to supply and maintain the air: fuel ratio for combustion.

On a carburetor, fuel injection is regulated by a fuel diaphragm manipulated by the rider’s throttle input, while a butterfly valve controls the airflow.

Carburetors require routine maintenance, or the butterfly valve can wear out and get stuck.

Once it gets stuck, the butterfly valve restricts the airflow, allowing excess fuel to pass through the carb and into the combustion chamber. The unburnt fuel can leak into your motorcycle’s oil supply until your dipstick smells like gas.

5. The Motorcycle has Faulty Piston Rings

Piston rings are circular cast-metal strips in the piston grooves on the outer cylinder walls.

The piston ring is the component responsible for sealing the gap between the outer edge of the piston and the engine cylinder wall, keeping the combustion chamber separate from the crankcase.

This ensures the fuel mix doesn’t flow into the crankcase and mix with the oil or that the oil doesn’t blend into the fuel supply.

All piston rings wear out eventually from engine vibration and rapid hot-cold temperature shifts. This is why your moto-manufacturer recommends inspecting your piston rings at particular service intervals.

If your piston rings wear down, the seal between the crankcase and the combustion chamber is broken. Not only can fuel leak into your crankcase and mix with your oil, but oil can enter your combustion chamber and burn up in your exhaust.

This will leave your oil smelling like fuel and your exhaust like burning oil. You may experience thick, discolored smoke from your exhaust system-  from oil burning up in the combustion chamber.

Your motorcycle’s oil level rapidly decreases as the true oil burns up with the fuel. You’ll also notice your bike consumes more fuel than typical, as the fuel is entering your oil reservoir.

This causes a dip in fuel efficacy along with the engine overheating simultaneously – a recipe for failure with one component after another.

Here are the signs that worn piston rings are the reason your motorcycle’s oil smells like gas:

• Increased engine oil consumption
• White/grey/thick black smoke from the exhaust
• Insufficient compression in the engine
• Reduced power and acceleration
• Piston slapping; metal clanking coming from the engine as the piston slaps the cylinder wall

6. Motorcycle is Passed Due for an Oil Change

If you’re lucky, your motorcycle oil smells like gasoline because it’s contaminated and needs to be changed.

As motorcycle oil runs through the engine, it heats up and cold down repeatedly. This process alters its chemical properties, darkening its color, coagulating its consistency, and tarnishing its smell until it smells like burnt gas.

Suppose your oil is at the point where it looks black and smells like carbon and gas; it has lost its lubrication and cooling properties. Change it asap to avoid engine overheating.

7. The Air: Fuel Mix is Running Rich

The most common reason a motorcycle’s oil smells like gas is due to what we call a rich fuel mixture.

Fuel-injected combustion engines drive most modern motorcycles. In fact, even older, carburated bikes still used combustion-powered motors.

A combustion motorcycle engine uses the combination of air, fuel, and ignition to create the explosive power needed to drive each cylinder’s piston cycle and keep your rear wheel spinning.

As the motorcycle’s ignition spark is powered by the battery and spark plug dynamic, it draws its air in through the air intake system, and the gas provides fuel in your tank.

To maintain even combustion power, your motorcycle’s combustion chamber receives a precise air-to-fuel ratio. If that ratio has more air than required, we say it’s running lean (on power).

Adversely, if the air: fuel mixture in your combustion chamber has too much fuel and not enough air, we say it’s running rich.

This is why routine ECU or carburetor tuning is so important; the delicate balance between atmosphere and fuel must be maintained for optimal engine operation.

 The amount of fuel being sent into the combustion chambers is commonly measured as an “air/fuel ratio” which is just like it sounds – a number representing the ratio of the amount of air to the amount of fuel being burned in the engine.

An internal combustion engine mixes fuel with oxygen in the air and then ignites that mixture with a spark plug. From a strictly scientific point of view, the optimum mixture of air and common gasoline is around 14.6 parts of air to every one part of fuel for an air/fuel ratio of 14.6:1. At this ratio and under the right conditions, all of the gasoline and all of the oxygen can burn leaving nothing except for the combustion products.

[Source: Cycledoctor.com]

Since there is only so much space inside the combustion chamber, if there is an excess of one, it’s at the cost of the other. And if one is blocked, the other is allowed to flow into the chamber freely to fill the empty space.

Whether your airflow is restricted or your fuel flow is unregulated, the excessive presence of fuel in a rich air: fuel ratio allows it into the combustion chamber.

If your air: fuel ratio runs rich, there’s more fuel in the combustion chamber than your spark can ignite. The excess fuel drains through the piston rings and mixes with the oil in the engine, draining down into the oil pan, and your oil will start to smell like fuel.

Sources

Air/Fuel Ratio – Cycledoctor

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