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Gents,
Just noticed that on opening the Engine oil inlet cap on the top half of the engine, while the engine is running, it emits oil smoke.

Is this natural? or a sign of a compression failure?

Why do you want to open the cap when the engine is running ?

How much smoke ? What color ?

OT:
Be very careful when engine is running. During the first attempt at adding Bardahl, we had tried to follow instructions to the 'T'. Engine running, opened the oil cap, started to add Bardahl. The oil flew out -and unfortunately towards the eye of the guy who was adding the oil.

Was the engine overheated when you checked because oil vapour would be present in that zone. Check the following, before reaching a conclusion.

• Oil level, is it dropping

• Exhaust condition, Is it emitting blue smoke.

• Remove the dip stick while engine is running to see if similar smoke is emanating.

It is called engine blow-by. For more information see this video.

Mercedes Turbo Diesel Blow-by test - YouTube

What mileage have you covered?

Yes its blow by and if its just smoke without oil spray then its beginning of compression loss which might require you to increase the viscosity of the oil. If on a hot engine there is a spray of oil from either the oil filling orifice or the oil dip stick then its time you sold the car or started saving to re-bore the engine and put new rings and sleeves and while at it you would be advised to change the engine crank shaft, cam shaft bearings and oil pump as well.

As mentioned before this is blow by air.

When the amount of blow by air can vary, in different cases, in NO cases there should be smoke. If so, the cylinder is 'leaking'.

btw, which vehicle/engine is it? and how strong is the blow-by air.

Blow by air also know as crank case ventilation it must be.

There is always small amount of gases escaping the piston rings during various strokes. These gases go down in crank case & in the crank case you have the crank shaft rotating which creates pressure.

So these gases are let into the engine head through a internal gallery. Even the head has camshafts rotating which develop some pressure. All these gases are let out through head from small pipes which go back into the intake manifold for complete combustion.

But these gases contain some amount of oil in it which should not go into the combustion chamber so modern cars have a thing called Air Oil Separator which is situated on engine head & these gases pass through this separator which separates the oil form these gases and let's it back into the head where as these gases flow into intake manifold.

So you see these gases coming out of the engine oil inlet cap when its opened.
In case of worn out piston rings more gases escape the rings during various strokes resulting in more blow by gases.

Let us know which car you are talking about and how many kms it has clocked.

Thanks for the responses.
Its my Ford Fiesta TDCi, 3 yrs old, 45,000 kms.
and it is under extended warranty till July.

It was a routine check after the injector bushes were replaced.

Its white/grey. There is just about enough smoke to notice when standing over the engine with Cap off.

Engine was warm, not overheated.
- Am still checking on oil
- No exhaust smoke

Shouldnt this be covered under warranty?
Really like my car and dont want to sell it!

Well, as Rajeev asked, after the engine warmed up, remove the engine oil check dipstick and see whether any blue/grey smoke is coming.

What are injector bushes? Why were they replaced?
Any smoke on cold start? How old is your engine oil? If more than 5000km old, replace oil and recheck for smoke on cold start.

Should be covered, but since this problem might mean a new set of rings (and maybe pistons & liners), the company or the service centre won't be too enthusiastic about obliging!

Is it possible to check the coolant levels of your car?

45K is nothing for the engine and if no untoward calamities had happened to your engine like overheating due to coolant leak, improper lubrication, then don't worry. Do the checks as suggested.
Engine gets covered under extended warranty.

What are injector bushes?
Yes, if you have a valid warranty.


btw, is there any power loss? Overheating?

I had mentioned the smoke to the dealership and the engineer who (replaced the bushes) told me that small amout of smoke from the engine oil inlet is natural. My dad thinks its not and its a sign that it will get worse.

There was a hissing noise from the engine, the dealer then changed all the bushes under warranty.
The engine oil was just changed a few hundred kms ago.

Coolant level is ok. Dealership checked earlier.
No perceivable power loss.. driving like a dream.
No overheating either.

I feel the oil level is dropping, they really topped it up above the markings on the dip stick so cant be 100% sure, am doing a check every week. Exhaust is completely fine.

There is a small amount of smoke emitting on removing the dip stick.

Better wait and watch and observe the KMs between topping up and level dropping to Minimum. Meanwhile lodge a warranty claim with the dealership.