Smoke coming from the oil filler cap – Why and how to fix it?

Do you have a car or knows someone that has a car which smoke comes from the oil cap when removed? Click here now to learn what this is and how to fix it

Are you seeing engine fumes when you open your engine’s oil filler cap? This isn’t in anyway good news for your car or the engine inside. So, the question is: What exactly does it even mean? Well, the answer is dependent on the amount of smoke you are seeing come out.

If the smoke is small, everything is probably fine, but if the smoke is kind of too much, then you should be concerned. To avoid unnecessary mechanic visits, brings here the best information as regards this problem and possible ways you can fix it. Read on.

smoke coming from an oil filler cap

This BMW refuses to start and releases smoke on oil filler cap

Smoke coming from the oil filler cap – How do you test for the smoke?

Well, this isn’t difficult as most people think. You can easily determine if the smoke you are seeing is a fatal sign or just something normal. This is how you test the smoke to be sure:

  1. Start up your car engine and then let the car stay idle for some time while you wait
  2. Slowly and patiently loosen the engine oil filler cap till you are able to completely remove it
  3. Now, pay attention to the amount of smoke/fume that is blowing out as you remove the oil cap.

At this point, if the amount of fume you can see coming out is less, then it’s probably fine like we mentioned earlier. But if the amount of fume is much, or it is even coming out with some pressure, then you should actually worry because that’s a bad sign. And if the vapor seems to even contain contaminated fume as well, please take that vehicle to the nearest servicing shop immediately.

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Some safety notes for you to keep in mind about the above testing method:

  • Do not open the oil filler cap when your car’s engine is hot. This is not advisable at all for safety reasons. On starting your car in step 1 above, don’t wait too much till the engine gets hot before you proceed to step 2. Just about 1-3 minutes is okay to wait.
  • When you are done with the test, remember to close the tank with the oil filler cap. Don’t forget and leave it open while you plan to take the car out. It’s dangerous.
  • Try to clean up any oil residue that is spilled around while you were carrying out the test. Cleanliness has its reward.

Image of an oil filler cap opened completely

To examine the smoke level coming from the oil filler cap, you need to remove the cap itself

Reasons why your engine emits smoke from the oil filler cap

There are two main possible reasons why your engine will emit smoke from the oil cap:

  1. When worn valve stem seals and rings have hot fuel bypassing them
  2. Or just fuel at any time bypasses the worn valve stem seals and worn rings

You should be aware of the fact that the specific amount of tolerance between the engine components determines how smooth the operations of such an engine will be at any given time. To keep all the parts moving smoothly without friction, the oil just has to flow to all the parts of the engine. The proper flow of oil in the system is what prevents the machinery from locking or seizing at any point in the operation. But soon, the components in the engine will start showing some signs of wear during usage and the seals will become thin from continuous usage.

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As a result of this, some crucial place like the combustion chamber will start to allow oil leakage because some of the games between the machine’s parts would have become too much wider than they should be. And, when the fuel drips through the valves and piston rings and gets into the combustion chamber in the process, with each firing shot of the fuel-air mix, smoke is produced. You will notice that the amount of oil leakage and smoke produced will increase as you accelerate to higher speeds.

Smoke coming from the oil filler cap – How do you fix it?

Like we mentioned earlier, there isn’t any rocket science knowledge required. You can easily fix it by following some simple steps we will be providing as you read on.

First, we advise that you check your piston rings and stem valves condition and then consider changing one or even both of them in case you notice that they are worn out or damaged. Actually, if you are faced with a situation whereby you noticed that only one of this part is worn out or damaged, we would advise you don’t only change that worn out/damaged one, rather please try to just change the two parts altogether.

Oil cap smoke?! OH NOES!

The reason why we will give this advice that replacing only one part with a new one while leaving the other old part as it is will only make the older part unable to keep up with the pressure that will be created by the new/ replaced part. This can later make the older part wear out quickly or eventually later get damaged too and then, you will now have it replaced, which is like what you avoided from the onset ?.

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Let’s look at an example to understand this better, say you changed only the stem valves, the pressure will be contained it should be because of your change. Nonetheless, extra pressure wouldn’t be able to pass through the old rings because the old rings wouldn’t show the same strength as it used to. And on the other way around, if you changed rings but keep the same old valves as it is, then the opposite of the effect of our example is what you will get at the end.

Our Conclusion

Remember, temporary fixes will keep draining you slowly out of money if all you do is to keep replacing only the affected part. You should try to just change all the components and parts related to a particularly affected part altogether, this will save you money if you think about it.

And if you happen to have a car that is releasing a huge amount of smoke together with contaminated fume from the oil filler cap, please don’t even consider replacing the affected alone as an option, rather just change all the related parts together with the affected part. And in this case, you can as well consider going for a used engine of your car’s brand and model which you have confirmed that it still has many miles left on it after its previous use.
That will be all for now buddy. Goodluck!