When fuel mixes with engine oil in the crankcase, the situation is referred to as “fuel dilution,” an alarming issue that can affect the performance and longevity of an engine.
The crankcase is an essential part of an internal combustion engine that stores oil for lubrication purposes. You do not want fuel to enter the crankcase if you want a healthy engine.
The unintended mixing of fuel and engine oil can occur for several reasons, leading to detrimental effects on the engine’s functionality.
In this post, we will unravel the causes of this problem and help you understand why it is crucial to address it promptly. Keep reading.
What Causes Fuel to Mix with Engine Oil in the Crankcase?
If fuel mixes with oil in the crankcase, it usually indicates a problem or malfunction within the engine. Several causes can lead to this issue. They include:
Leaking Fuel Injector
When a leaking fuel injector develops a leak, it does not seal properly, allowing oil to escape into areas it should not.
A leaking fuel injector can allow fuel to pass through its nozzle even when the engine is not actively injecting oil into the combustion chamber or running.
The situation usually happens because of a faulty valve, damaged or worn-out injector seal, or debris that hinders the proper closure of the injector.
When the engine is off or idle, the leaking fuel injector continues dripping fuel. This fuel enters the manifold, valves, or down the cylinder walls.
From there, when the engine is in operation, the fuel can bypass piston rings and mix with the engine oil in the crankcase.
Cold Starts
Fuel dilution can occur during cold starts. When the engine is cold, its combustion process is not as efficient as it is at normal operating temperatures.
As such, the fuel injected into the combustion chamber may not burn completely, leading to unburned fuel passing and entering the crankcase.
It is important to note that fuel dilution during cold starts is usually a temporary situation. When the engine warms up and reaches its operating temperature, the combustion process becomes more efficient. This reduces the likelihood of fuel dilution.
Faulty Fuel Regulator
A fuel regulator maintains proper pressure and flow of fuel to the engine. If it malfunctions, it can lead to excessive fuel in the combustion chamber.
Should that happen, some of the fuel may not burn completely. The unburnt fuel then passes by the piston rings and enters the crankcase contaminating the engine oil.
Faulty Piston Rings
Piston rings seal the combustion chamber, preventing fuel and air from entering the crankcase. However, over time, the piston rings can wear out or get damaged because of factors like poor maintenance or engine overheating.
When the rings wear, they lose their ability to create a proper seal. As such, unburnt fuel and combustion byproducts from the combustion chamber escape into the crankcase.
Engine Misfires
A misfiring engine can also cause fuel to contaminate oil in the crankcase.
When an engine misfires, unburned fuel can enter the exhaust system and accumulate in the catalytic converter. Over time, this fuel can seep past the piston rings, contaminating oil in the crankcase.
Extended Engine Idle
At idle, the engine operates at a lower load and lower temperature than normal. This can result in incomplete combustion, where the unburned fuel can escape past piston rings and into the crankcase.
Additionally, when the engine idles for a long time, the unburned fuel has enough time to pass through the piston rings and combine with the oil in the crankcase.
The longer the engine idles, the higher the chances of fuel dilution occurring.
What Happens when Fuel Mixes with Engine Oil?
When fuel mixes with engine oil, it dilutes the oil, degrading its quality and properties. Remember, fuel is a solvent, and when it combines with oil, it acts as a thinner.
This reduces the oil’s lubricating properties, compromising its ability to protect the engine effectively.
With diluted engine oil, the lubricating properties are reduced. As such, the oil film may not effectively separate metal surfaces in the engine.
The result is increased friction and wear on engine parts like bearings, pistons, and camshafts.
Excess fuel in the engine oil can also alter the air-fuel ratio, causing incomplete combustion and reduced engine efficiency. And if the oil contains impurities, it can contaminate the oil.
Fuel dilution can also cause oxidation and thermal breakdown, minimizing the oil’s ability to resist viscosity changes and preserve its protective properties.
How Do You Know that Fuel is Mixing with Oil?
The signs and symptoms of fuel dilution vary depending on the severity of the problem. Here are some common signs to look out for:
Increased Oil Level
If you notice that the oil level on the dipstick has increased unexpectedly, it could indicate fuel contamination.
Thin or Watery Consistency
Fuel dilution tends to thin out the engine oil, giving it a watery appearance. If your engine oil seems thinner than usual, it could be fuel dilution.
Reduced Lubrication Properties
When fuel mixes with engine oil, it can degrade the lubricating properties of the oil, leading to increased wear on engine components. This can result in increased oil consumption and poor engine performance.
Increased Oil Foaming
Fuel-contaminated oil can cause excessive foaming and disrupt oil flow and lubrication. Should this happen, you will see foam when inspecting the oil cap or checking the oil level on the dipstick.
Fuel Odor
If you sense a strong gasoline smell when running your vehicle or checking the engine oil, it could be fuel contamination. The odor is usually noticeable from the dipstick or when the oil filter cap is removed.
Poor Engine Performance
Fuel dilution can affect the combustion process and cause reduced engine performance. You will experience reduced power, rough idling, misfires, or poor fuel efficiency.
How Can You Prevent Fuel from Mixing with Oil in the Crankcase?
To prevent fuel from mixing with oil in the crankcase and affecting your engine’s performance, consider the following measures:
- Follow a regular maintenance schedule for your vehicle.
- Always use the correct fuel as recommended by your vehicle’s manufacturer.
- Avoid short trips, especially in cold weather, as they can contribute to fuel dilution.
- Monitor excessive idling to prevent unnecessary fuel contamination.
- If you see signs of engine problems such as unusual exhaust smoke, misfires, knocking sounds, and reduced efficiency, consult a qualified mechanic, and address the issues promptly.
- Avoid overfilling the fuel tank, as the excess fuel can find its way into the oil.
Conclusion
The presence of fuel in engine oil can be a concerning issue. The problem can arise from factors such as worn piston rings, an overfilled fuel system, or faulty fuel injectors.
When fuel combines with engine oil, it compromises the lubricating properties of the oil and its overall performance.
Therefore, it is important to address the problem promptly, by rectifying the underlying issues for optimal engine performance and longevity.
