Air Coming Out of Oil Cap – Causes & Fixes

Have you ever opened your oil filler cap You felt an immediate rush of pressure or air coming out of the hole. This is perfectly normal, even though there is less air. It is caused by the pressure of the crankcase moving engine parts.

If the air volume is too high, it could be caused by faulty piston rings, or a clogged valve.

These characteristics are indicators that you should be more concerned with the air coming out of the oil cap.

  1. After removing the oil cover, the air you get out smells strongly like fuel.
  2. When you open an oil cap, you will hear a hissing sound or leaking gas.

Let’s now look at the reasons why air escapes from the oil cap.

Causes of air coming out of an oil cap

Piston rings worn out 

Piston ring seals that are worn can let air escape from the oil caps. Piston cycles seal piston against the cylinder walls. These piston ring seals keep oil in the oil sump, allowing oil to splash onto engine parts below to ensure proper oil lubrication. They store compressed air when the crankshaft drives the piston rings. 

The compressed air can seep back into your oil sump if the piston rings seals are working correctly. If the seals fail, compressed air may pass through the piston rings during cycling. This compressed air can then flow into the oil-fill tube. If the amount of compressed air is too large, air can escape from the oil fill tube when it is opened.


Replacing the piston rings seals is the only way to fix this problem. By having the piston ring removed by a mechanic, you can find the right size. It is important to remove all seals from the piston-ring. This will allow the mechanic determine the proper size seal that will fit the compressor piston. Replacement costs for the piston rings can run from $1,000 to $5,000.

Clogged PCV valve

The primary function the PCV valve serves is to keep air from escaping. It routes fuel and air from crankcase to intake manifold. The PCV valve can become clogged and cause engine pressure to rise if it is not working properly.

It’s easy to find out if your PCV is blocked. It is best to remove the oil filler cap (preferably when). engine is cool and not hotIf there is slight suction when opening the valve, it will work properly. If you feel pressure while opening the oil cap, your PCV valve may be clogged.

Clean the PCV Valve to eliminate the possibility of air leaking from the cap. Let’s look at how to clean the PCV Valve.

  1. The valve cover usually has the PCV-valve. Use a screwdriver to loosen the bolts of the PCV valve. You must remove it from your air intake.
  2. To see the parts clearly, take off the caps on the PCV valve.
  3. Use brake fluid or carburetor cleaning to clean the parts of your PCV valve.
  4. Use compressed air to blow any liquid out of the PCV valve.
  5. Reinstall the cleaned PCV Valve.

FAQs about Air Coming Out Of Oil Cap

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It is normal for some air to come out of the oil filler cap after you remove it. You should not have too much air. Your piston rings or engine’s PCV valve could be damaged. Sometimes you can spot it. sludge on the filler cap This could be due to other causes. This should be checked.

You can easily clean a clogged PCV valve with brake fluid. The only way to fix the piston rings is to have them replaced. For the replacement of piston rings, it is advisable to contact a professional.

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