When the lubricant level in the crankcase suddenly rises and the probe smells of gasoline, it always causes panic in the car owner. It is not just a minor malfunction, but a serious symptom, the neglect of which can lead to major repairs to the engine or even its complete replacement. In injection systems, this process often occurs secretly until the concentration of fuel in the oil reaches critical values, changing the viscosity and lubricating properties of the fluid.
The mechanism of fuel penetration into the crankcase on modern injection systems differs from carburetor analogues in its complexity and dependence on electronics. nozzle Or through the gaps in the cylinder-piston group, where fuel drains when the engine is not working or is washed off the walls when the launch attempts are unsuccessful, and understanding the physics of this process is the first step to a competent diagnosis.
In this article, we will take a look at all possible scenarios, from the banal flood of candles to complex problems with the engine control system, you will learn how to distinguish natural wear from critical failure and what actions you need to take immediately to save the power unit from costly consequences.
Physics of the process: how the fuel is in the crankcase
In a proper internal combustion engine, the fuel must burn up in the combustion chamber, creating pressure that pushes the piston. However, some of the gasoline inevitably settles on the cylinder walls and enters the crankcase space. Under normal conditions, this gasoline has time to evaporate due to the high temperature of the engine running and the ventilation system of crankcase gases. Problems begin when the amount of fuel exceeds the system's ability to dispose of it.
The main reason for mixing is condensation The fuel is not burned on the cylinder walls, which then flows down the block walls into an oil pallet, and in injection engines, this process is exacerbated by the fact that the fuel ramp is under high pressure even after the engine stops. If the nozzle stop valve does not hold the pressure, the gasoline literally drips into the cylinder, and from there through the piston rings seeps into the oil.
Another important aspect is the engine's modes of operation: on frequent short trips, when the engine does not have time to warm up to operating temperature, gasoline evaporation from the oil practically does not occur, resulting in what is called "oil liquefaction", when its viscosity drops and the lubricating film becomes too thin to protect the rubbing vapors.
⚠️ Attention: If you notice that the oil level on the probe has risen above the maximum mark and smells of gasoline, the car should be stopped immediately, and further operation of the engine with such oil will lead to a twist of the crankshaft liners.
The design of the injection system is also worth considering: Unlike a carburetor, where fuel is supplied by gravity or at low pressure, an electric fuel pump operates here, creating pressures from 3 to 5 atmospheres (and in direct injection systems - up to 200 atmospheres), Any leakiness in such a system leads to a rapid loss of fuel in the crankcase.
Why is this happening more often in winter?
In cold seasons, the evaporation of gasoline decreases and the engine takes longer to warm up, and at low temperatures, the ECU forcibly enriches the mixture for stable start-up, which increases the amount of unburned fuel draining into the crankcase.
Failures of the ignition system as a catalyst for the problem
Often, owners look for a problem in the fuel system, forgetting that in order to get gasoline into the oil, it must not burn first. The main culprit is the ignition system. If the spark is weak or absent, the mixture remains unburned and settles on the walls. Diagnosis begins with a visual examination. spark plug.
Turn the candles out and notice their color and their carbon, and if the electrodes are black, wet and smell like fuel, it means that the mixture does not ignite in this cylinder, and the reasons can be trivial: a breakdown of high-voltage wires, a malfunction of the ignition coil or ignition module. In modern engines with individual coils, the failure of one of them immediately leads to tripling and fuel injection into oil.
And don't forget the gap of the candle. Too much gap requires a higher voltage to break down, which the old coil may not provide, and the timing and state of the thread are also important. The wrong potassium number of the candle can lead to a potassium ignition or, conversely, to too low temperature in the combustion chamber, which prevents full combustion.
Special attention should be paid to the crankshaft position sensor, and if it fails, the ECU may misidentify the moment of spark formation, which will lead to a misfire, in which case the gasoline will be pumped into the cylinder, but ignition will not occur, and the fuel will go into the crankcase.
Problems with nozzles and pressure regulator
The most common technical reason for gasoline to enter the oil on an injector engine is the leakyness of the fuel injectors. Over time, the shut-off cone of the spray needle wears out or becomes covered with solid deposits that prevent the valve from closing tightly, and even a microscopic gap under high pressure turns into a constant jet of fuel.
You can test the leakage of the injectors by putting pressure on the fuel ramp and looking at the pressure gauge, and if the pressure drops faster than the pump is designed to go off, there's a leak somewhere. fuel pressureIf its membrane is torn, the gasoline is directly sucked through the vacuum tube into the intake manifold and from there into the cylinders.
The symptoms of a pressure regulator malfunction are often disguised as pump problems: the engine stalls, it's hard to start, it loses power. But if you add the smell of gasoline in the oil and the black smoke from the exhaust pipe, the diagnosis becomes obvious. The replacement of the regulator is a procedure that is inexpensive, but critical to the health of the engine.
| Malfunction | Probability of fuel hit | Characteristic |
|---|---|---|
| Sticking of the nozzle needle | High. | Cold-cold friction, overspending |
| Rupture of the RDT membrane | Medium | Black smoke, unstable idling |
| The DIS malfunction | Medium | Floating speeds, jerks during acceleration |
| Coil failure | High. | Trotting, engine vibration. |
Also worth mentioning is the purity of the fuel injectors, which are clogged with the wrong spray torch, so that the fuel doesn't evaporate instantly, but settles in droplets on the walls of the intake manifold and valves, then draining into the crankcase.
The influence of the electronic control unit and sensors
A modern injection engine depends entirely on the readings of the sensors that it processes. EBOU If the oxygen sensor (lambda probe) gives the wrong reading, the control unit can artificially enrich the mixture, believing that there is too much oxygen in the exhaust, and the excess gasoline in this case simply does not have time to burn.
The coolant temperature sensor (CTP) plays a key role in the formation of the mixture at start-up. If it lies and shows that the engine is cold when it is already warmed up, the ECU will keep the enriched mixture warm-up mode indefinitely, which is a direct route to quickly saturating the oil with gasoline.
Mistakes in the firmware of the control unit can also be a cause: Incorrect fuel table maps, especially in tuning or “crooked” chip engines, lead to overflow. Diagnostics with a scanner will help you see the real values of fuel correction: if the long-term correction goes into a strong negative, then the system is trying to compensate for over-enrichment.
Mechanical damage and engine wear
Nor should the mechanical problems of the engine be discounted: wear on piston rings or bullies on cylinder walls reduce compression; low compression means the mixture is poorly compressed and burns even worse; the unburned part easily crosses the ring barrier and enters the crankcase.
Valve problems, such as burnout or loose fit, also contribute to this process. If the exhaust valve does not hold, some of the fuel-air mixture can be thrown directly into the exhaust manifold, but when the intake stroke through the looseness, a reverse pump can occur, which disturbs the balance.
It is important to check the condition of the crankcase gas ventilation system (PCV). If the PCV valve is jammed in the open position, an excessive vacuum is created in the intake manifold, which can literally "pull" oil and fuel vapors out of the crankcase, disrupting the balance and promoting mixing.
⚠️ Attention: If there are mechanical injuries (blowers, finger-thumping), further operation of the engine is unacceptable, and simply replacing the oil will not solve the problem, but only delay the overhaul by a couple of hundred kilometers.
Methods of diagnosis and elimination of malfunctions
Diagnosis should start with the simplest and most accessible, the oil and candle state, the compression check will help to rule out mechanical problems, if the compression is normal, go to the fuel system, take the pressure in the ramp and check the pressure retention after the pump is turned off are mandatory procedures.
To accurately determine the pouring nozzle, you can use an ultrasonic wash bath or a special stand where you can see the spray torch. At home, you can use the exclusion method, turning off the nozzles one by one and watching the engine work, although on modern systems this can cause errors.
Once the cause is eliminated, you need to double-change the engine oil, the first one works as a flush, the second one works as a primary one, and the oil filter needs to be replaced, because the gasoline could dissolve the old filter's rubber seals.
Consequences of ignoring the problem
Many drivers mistakenly believe that if the engine is running and not knocking, you can drive to the service. But the gasoline in the oil acts as a solvent. It washes the additives out of the oil and destroys the oil film, and as a result, rubbing parts like the camshaft, rockers and crankshaft liners begin to operate in dry friction mode.
This results in accelerated wear and eventually, rod liners or engine jamming, which is much more expensive to repair than replacing a nozzle or sensor in a timely manner, and the gasoline in the oil reduces its flash point, which increases the risk of fire if the lubrication system depressurizes.
To sum up, gasoline in oil is always a signal of a malfunction of the power or ignition system. A competent approach to diagnosis, including checking electrical, mechanical and electronics, will quickly find and eliminate the cause, saving the life of your car.
Can I drive if the oil smells like gasoline?
Not recommended, even a short trip can lead to the liners turning around, and if a problem is found on the way, it is better to call a tow truck or add fresh oil to the level to get to the nearest service at minimum speed, but the risk remains high.
How quickly will gasoline evaporate from the oil when heated?
Natural evaporation is possible only with prolonged operation of the engine at high temperature (more than 90-100 ° C) for several hours. However, if the cause of the gasoline supply is not eliminated, this process is useless.
Does the quality of gasoline affect this problem?
Yes, bad gasoline can contain resins that clog the nozzles, disrupting the tightness of their closure, and a low octane number can cause detonation, which the ECU will try to compensate for by changing the angle of ignition, which indirectly affects the completeness of combustion.