Is air coming out of the oil cap? These are the causes

For most vehicles, it is assumed normal to have air blowing out of the oil filler cap because of all the pressure caused by the movement of parts in the crankcase.

However, the problem begins when this air comes out with high pressure and is accompanied by fuel-like smells and hiss sounds.

This event may mean that the engine piston rings are worn out, which could be a bad sign, especially for engines with high mileage. 

All vehicles have a blow-by mechanism where air escapes with minimum pressure due to movement. The extreme case is an indicator that the engine might have an issue.

Below are explanations concerning the air coming out of the oil cap scenario and the possible solutions you can implement to avert any problems that might arise. 

Why Air Comes Out of an Oil Cap

Air from the oil cap is considered a normal phenomenon in most vehicles. Consider the engine’s design and structure. The movement is caused by the pistons when they move up and down the cylinders.

Remember that the piston’s bottom is usually exposed to the oil pan. Similarly, the air gets moved by the pistons’ top, and the same happens to the bottom. Suppose you pull off the valve cover and see straight down the oil pan. 

When the oil cap is opened, the air gets a path of least resistance, escaping. When the vehicle moves, various parts, including the oil cap, move if it is not tightly fitted, leading to air escaping.

Blow-by is the primary reason air escapes from vehicles’ oil caps. The only difference between this situation is average and not the amount of pressure that the air comes out with, and if it is too much, then it should be a matter of concern. 

Should Air Be Blowing Out of the Oil Cap?

Modern engines are equipped with positive crankcase ventilation (PCV), which is critical in maintaining lower pressure in the crankcase than the atmospheric pressure.

This role is attained under normal functions, which allow the different vehicle parts to function as required. Upon removal of your oil filler cap, it is normal for you to feel some slight suction.

However, if you feel pressure instead of the suction, you need to check the PCV valve for any issues. Once it is verified that there is no issue with the valve, you should be concerned about excessive blow-by. 

Typically, the air coming out of the oil cap is considered normal, but the concern begins when the pressure is too high. Normal blow-by is okay and only demonstrates support for the internal functions.

When the air coming out is too much to lift the oil in the fill hole, there is a problem. This issue could result in blowing oil pan gaskets, different seals, and valve cover gaskets, which could significantly damage your vehicle.

Air should be coming out of the oil cap, but only at a considerable rate where the pressure is not too high, and when it reaches this level, it becomes an issue that requires immediate attention. 

Symptoms to Alert the Driver

Once the driver smells fuel in the car, checking the oil cap and the possible issues causing too much air to escape, carrying some power with it is a symptom.

Suppose there is too much air from the oil cap; some fuel may move out. When the fuel vapors are enough, the driver can sense it which means a major sign that something could be an issue.

Another sign is the engine light. An illuminated check engine light can alert the driver about evaporative emissions issues, allowing the driver to check for a leak in the system and avoid future problems.

A cap that does not tighten properly is another symptom. Suppose the driver tries to fit this cap, which does not fit well, then it indicates that excessive air could be blowing out of the oil cap. 

Solutions for the Causes

Suppose the driver notices that the oil cap fits loosely; the best solution is to change the cap or ensure that they fit it well enough in case a human error causes the fitting issue.

Staying alert for the check engine light and ensuring effective assessment of all the possible issues is another solution to ensure that the amount of air coming out of the oil cap is minimum.

Inspect for the source of fuel smell in the vehicle. This strategy effectively assesses the vehicle for other sources besides the oil cap.

This approach could expose other possible issues with the engine, allowing earlier fixture of issues. If these approaches do not solve the issue, the driver should schedule a fuel system inspection with professional mechanics to fix the excessive air issue.

Final thoughts

While an oil cap issue cannot cause significant problems when driving, it is vital to have your vehicle checked when excessive air blows out of the cap. You should stay alert for any symptoms to ensure mitigation through effective assessment.

Suppose you are experiencing any of the oil cap issues described and apply the solutions without results, consider seeking the help of professional mechanics. Ensure regular servicing of your vehicle to limit vehicle problems.

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