If your car engine oil smells like gas, it is possible that gasoline has entered the crankcase and mixed with the engine oil. When the engine oil is diluted with gasoline, it loses its ability to lubricate parts such as the bearing surfaces, cylinder walls, camshafts, etc.
While some fuel may enter your car’s oil from cold starts, if you have a strong gasoline smell in your car’s oil, this could indicate a problem with either a leaky fuel injector, too much fuel being delivered to the engine (a rich mixture), the engine misfiring or simply too many short trips.
Additionally, if the oil level in your car’s crankcase is rising, this is another indicator that gasoline is entering the crankcase and adding to the volume of fluid in the crankcase. Car engine oil smells like gas when fuel gets into the oil, although the amount of fuel can vary depending on the cause.
How Gasoline Enters Engine Oil
Gasoline is delivered to each cylinder by means of the fuel injectors. Engine oil circulates throughout the crankcase and through oil passages. Between the combustion area and the crankcase are the piston rings. These rings permit a small quantity of fuel to enter the crankcase, particularly during the initial stages of cold operation.
Some of this fuel will evaporate from the engine oil once the engine reaches normal operating temperature. If a significant quantity of fuel remains in the engine oil after evaporation occurs, it will remain in the engine oil.
When car engine oil smells like gas, repeated fuel entering the crankcase can increase the amount of gasoline mixed with the oil.
Frequent Short Trips and Cold Starts
A cold engine requires extra fuel during startup. If you operate your car infrequently and turn it off after a short distance, your engine oil will most likely be at a low enough temperature that it will not effectively evaporate a large portion of the fuel contaminants.
Repeated short trip operation will result in an increase in the quantity of fuel that is diluted into the motor oil.
Short trip operation is especially common in automobiles that are utilized primarily for commuting to work, driving children to school or for making frequent trips through a city.
Repeated short trips can therefore contribute to situations where car engine oil smells like gas, even when there is no failed mechanical component.
Leaky Fuel Injectors
If your fuel injector is not delivering fuel to a cylinder, it should be sealed. If an injector permits an excessive quantity of fuel to enter a cylinder, it is considered to be leaking.
The fuel can flow down the sides of the cylinders and enter the crankcase.
A leaking injector could potentially lead to:
- Difficulty starting the engine
- The engine idles erratically
- Poor fuel mileage
- An obvious gasoline odor from the tailpipe
- An illuminated check-engine light
When these symptoms exist simultaneously, the fuel injectors will most likely be one of the components that a technician will examine.
A leaking injector is one possible reason car engine oil smells like gas, particularly when the oil level also begins to rise.
Excessively Rich Fuel Mixture
The engine’s control system meters the amount of fuel it delivers based upon the volume of air entering the engine, the engine’s temperature and other sensor readings.
A malfunction may occur resulting in the engine receiving greater quantities of fuel than needed. Excess unburned fuel can also travel from the cylinder into the crankcase.
Excessively rich mixtures can occur as a result of faulty fuel injectors, oxygen sensors, coolant temperature sensors and other malfunctions with your vehicle’s engine control system.
A diagnostic scan tool test and fuel system tests can aid in identifying the cause of the malfunction.
A rich mixture can also contribute to a situation where car engine oil smells like gas because excess fuel may reach the crankcase.
Misfiring Engine
Fuel will enter a cylinder that is misfiring but cannot burn it completely.
Worn out spark plugs, defective ignition coils, problems with fuel injectors and other technical problems that prevent the engine from functioning properly can result in engine misfires.
Excess unburned fuel reaches the cylinder walls and passes through the piston rings into the crankcase.
A consistent misfire can also send unburned fuel into the exhaust system, potentially damaging the catalytic converter.
A misfiring engine is another possible reason car engine oil smells like gas, especially when the misfire continues for an extended period.
Indicators of Fuel Contaminating Engine Oil
A strong gasoline smell
The dipstick is a simple location to detect this odor.
Park your vehicle on flat ground with the engine shut down and check the engine oil with the dipstick as instructed by your vehicle manufacturer.
A strong gasoline smell from the engine oil differs from a faint fuel smell after a cold start.
If car engine oil smells like gas strongly on the dipstick, the oil should be checked further rather than relying only on the smell.
An Increasing Oil Level
Engine oil levels should remain between the minimum and maximum marks on the dipstick.
If the level of engine oil increases without adding additional engine oil, another substance is likely entering the crankcase.
Gasoline is one such substance. Coolant contamination can also cause an increase in engine oil levels.
A rising oil level together with car engine oil smells like gas is a reason to have the fuel system and engine checked.
Thin Engine Oil
Gasoline reduces the viscosity of engine oil.
Thinning of engine oil due to dilution with gasoline can result in engine oil becoming noticeably thinner.
Do not attempt to determine whether or not your engine oil is diluted with gasoline by rubbing engine oil between your fingers.
Oil analysis can provide more precise measurements of fuel contamination than visual inspection alone.
Decreased Fuel Economy
Decreased fuel economy may result from either a leaking fuel injector or an overly rich mixture in the engine.
If fuel economy decreases concurrently with the development of a gasoline smell in your engine oil, you should inspect your fuel system.
Erratic Operation of Engine
Problems with your fuel system may result in erratic idle, hesitation or difficult starting conditions or misfiring.
These symptoms do not prove that gasoline has entered into your engine oil; however, they may indicate that there is a common underlying problem that is causing both erratic operation and fuel dilution.
Rapid Check if Car Engine Oil Smells Like Gas
Before assuming that your engine has a serious internal defect, perform these rapid checks:
- Engine Oil Level: Park on level ground, shut down your engine and check your engine oil level with your dipstick as directed by your vehicle manufacturer. An engine oil level above normal limits indicates that there is a problem.
- Gasoline Smell: A strong gasoline smell is more serious than a faint gasoline smell after a cold start.
- Condition of Engine Oil: Thinning of engine oil or significant changes in its condition should be examined by a qualified technician.
- Engine Operation: Erratic idle, hesitation or difficult starting conditions or a check-engine light may indicate problems with either your fuel system or ignition system.
- Recent Driving Patterns: Short trips (only a few minutes) may contribute to increased fuel dilution without failure of any mechanical components.
- Fuel Consumption Rates: A rapid increase in fuel usage may indicate problems with your fuel system.
These checks can help when car engine oil smells like gas, but they cannot accurately measure the quantity of fuel in your engine oil.
The above checks cannot accurately measure the quantity of fuel in your engine oil; however, they assist you in determining what additional checks need to be performed next.
Effects of Fuel in Engine Oil
Engine oil must maintain a certain viscosity to protect components that move within the engine.
When gasoline mixes with engine oil, the viscosity of engine oil decreases. The protective film between metal components may become weakened, resulting in greater wear of engine components.
Heavy fuel dilution can also diminish the capability of engine oil to withstand heat and pressure created within the engine.
A small quantity of fuel after multiple cold starts is significantly different from heavy contamination resulting from a leaking fuel injector or other malfunction.
When to Cease Driving Immediately
Cease driving and schedule an inspection of your vehicle if your engine oil level has increased beyond maximum limits specified by your vehicle manufacturer, your engine is misfiring excessively or your engine oil has a strong gasoline smell combined with other problems with your engine.
Rising engine oil levels can signify that a substantial quantity of fuel has entered into your crankcase. Excessively diluted engine oil can contribute to excessive wear internally within your engine.
Cease driving if your check-engine light is blinking, your engine is operating erratically or you experience a loss of power.
A blinking check-engine light can signify an active misfire that can potentially harm your catalytic converter.
If your engine oil level has exceeded maximum limits specified by your vehicle manufacturer, do not simply drain some engine oil and continue driving. You must locate and correct the source of the fuel contamination.
If car engine oil smells like gas strongly and the oil level is also rising, the vehicle should be inspected before continued driving.
A faint gasoline smell after a cold start without other associated symptoms can occur when a vehicle travels short distances frequently. A strong gasoline smell or rising engine oil levels necessitate additional investigation.
Techniques Utilized by Technicians to Detect Fuel Dilution
Technicians can utilize various tests to ascertain the source of fuel dilution.
When car engine oil smells like gas, technicians can use these tests to determine whether fuel is entering the crankcase.
Fuel Injector Testing
Technicians can test fuel injectors for leakage, fuel pressure and proper function.
Misfire Testing
A scan tool can identify current and historical misfire codes.
Technicians can then inspect spark plugs, ignition coils and fuel injectors based upon the nature of the misfire symptoms exhibited by your engine.
Fuel Trim Testing
A scan tool can display short-term and long-term fuel trim readings.
Abnormal readings can suggest issues with either delivery of fuel, air intake or sensor readings associated with your engine.
Engine Oil Analysis
Laboratory analysis of engine oil samples can assess fuel dilution and provide information regarding the overall condition of your engine oil.
Laboratory analysis of engine oil samples is considerably more effective at evaluating fuel contamination than relying solely on visual inspection of engine oil samples.
Can an Oil Change Resolve Fuel in Engine Oil?
An oil change eliminates contaminated engine oil; however, it does not repair the source of fuel entering your engine oil.
A leaking fuel injector requires repair or replacement.
Misfiring requires correction of the underlying ignition system malfunction (ignition coil failure) or engine malfunction (malfunctioning sensor reading).
An overly rich mixture requires correction of the underlying fuel delivery malfunction (malfunctioning sensor reading).
Upon completing repairs related to malfunctions identified above, replacement of contaminated engine oil and replacement of contaminated engine oil filters may be necessary.
An oil change alone will not solve the problem if car engine oil smells like gas because fuel continues to enter the crankcase.
Methods for Reducing Fuel Dilution
Short distance travel increases the duration that an engine operates at less than optimal temperatures during warm-up periods.
Combining short distance travels can reduce repeated cold starts.
Maintaining proper maintenance schedules for your engine can also help reduce the likelihood that malfunctions within your fuel system and/or ignition system will result in excessive amounts of fuel entering your crankcase.
Regularly monitor your engine oil level, particularly if you notice any changes such as erratic idle/hesitation/difficulty starting/check-engine light illumination and/or decreased fuel economy.
If car engine oil smells like gas, monitoring the oil level can help identify whether the amount of fluid in the crankcase is changing.
