So you’ve noticed engine oil leaking? One of the causes could be oil leaking from the oil filler cap. In this article, we’ll look at some causes of oil leaking from the oil filler cap. We will also review some of the fixes for oil leaks from caps.

The oil filler cap is a small plastic cap on the valve cover. The oil filler cap is critical in preventing oil from splashing out of the engine. It is also crucial to keep dirt and debris from entering the oil.

If the oil filler cap is not functioning correctly, Oil will leak from the engine causing the oil pressure to drop(sometimes it can drop at idle). Oil can also leak onto other engine components, causing a vacuum leak or engine damage.

How to Detect Oil Filler Cap leaking

If you suspect oil leaking from your oil filler cap, you should inspect it. Examine the outer surface of the oil filler for any oil stains. Small oil stains may occur due to spilled oil during the oil change. However, if the oil patches persist after cleaning the filler cap, the oil is most likely leaking.

Other possible symptoms of oil leaking from the oil filler cap include: 

  1. Oil patches under the surface where the car is parked 
  2. Engine overheating more than usual
  3. The low oil pressure light comes on.

Reasons For Oil filler Cap Leaking

  1. The pressure on the crankcase increases as the engine runs at high rpm or the oil tank is overfilled. This can result in excessive pressure on the oil filler cap, resulting in broken seals.
  2. The oil filler cap’s O seal ring can break and dry over time, causing oil to leak from the cap.
  3. Another cause of oil leaking from the oil filler cap is a loose installation. The vibrations caused by the car running can cause oil to leak from the oil filler cap if installed loose.
  4. The combustion gasses can enter the crankcase due to broken piston rings or engine bores. Gravity causes oil to accumulate in the engine sump. These combustion gasses can force oil to push up from the sump and get through the oil filler cap, resulting in an oil leak.

How to Fix Oil Filler Cap Leaking

The most common cause of engine oil leakage is damaged seals. If the seal is no longer repairable, your only option is to purchase a new oil filler cap. This is because oil filler cap seal replacement is extremely difficult.

However, if the plastic washer around your cap’s seal is worn out, your oil filler cap may be repairable.

Here are the steps to repairing your oil filler cap:

  1. Remove or open your engine’s oil filler cap.
  2. Locate the washer in the oil filler cap. A washer is a round piece of plastic located with the sealing.
  3. Remove the washer by lifting the seal with a screwdriver. Take care not to damage the washer’s sealing.
  4. Reinstall the washer, but this time upside-down. The opposite side of the plastic washer is almost certainly not worn out.
  5. Reinstall the oil filler cap if you find that the cap is properly fitted and tight. Your oil leak problem has most likely been resolved.

If you still have trouble with the leakage, the best solution would be to have it inspected by your nearby mechanic.

FAQ’s on Oil Filler Cap Leaking

No, removing the oil filler cap should be no pressure. This usually happens when the oil tank is overfilled.

When you remove the cap, there should be a slight suction. This suction is caused by a small amount of air remaining in the tank, which is important. If you feel pressure, it could mean that the cap's seals can get damaged in the future, and oil can get leaked from the filler cap due to excessive pressure.

The oil filler caps are unlikely to wear out unless they are cracked or broken. Overfilling the oil tank can also cause enough pressure on the seals of the cap to break them down. The life of an oil filler cap is usually determined by the conditions under which you drive, but under normal conditions, the cap can last up to 100,000 miles.

The oil filler cap is on the top of the valve cover. It is easy to find because this is where you pour your engine oil. It is typically located on the driver's side of the engine bay.


To summarize, leaking oil can result from a faulty oil filler cap. The oil filler cap is used to avoid oil spilling from the engine, prevent dirt and debris from entering the oil, and used to check the oil level with a dipstick. 

Excessive engine pressure can damage the seals of the oil filler cap, resulting in leaking oil. Overheating and low oil pressure issues in the engine can be caused by leaking oil. If the seals cannot be repaired, purchase a new oil filler cap.

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