Engine blowing air through the oil filler cap

ocelot83

Hi all,

I am looking to buy an audi a4 car second hand. I found and have looked at a car that i would like to buy. However when the engine is running and i remove the oil filler cap there is a lot of air being blown out (and even a small bit from the dip stick). To me it seems that there must be a poorly seated valve(s) allowing air to escape from the compression chamber. Is this a common thing on audi a4 1.9 engines (B6 model) or is this car just not worth the hassle?

Cheers

Schism

I'm by no means an expert but the general rule is stay away in such a situation, not worth the hassle. Correct me if I'm wrong.

Johntegr

Would it not be a bad idea to remove the oil cap when the engine is running?

Bobo78

As far as I heard that is normal for VAG 1.9 tdi engines but I m not 100% sure about that.

thats not gone well

thought the norm was for engines do suck in a small bit of air through the filler when running?
could just be for petrols though

Johntegr

An engine is a pressurised system. The oil cap is there for a reason. That pressure helps circulate oil into the nucks and crannies. By pulling the cap off you're letting that pressure out and that's the noise you're getting. It's normal.

If you're concerned, have the engine compression tested.

ocelot83

thanks for the replies

I have no experience with audi / voltwagan engines but i have a mitsubishi colt and when the engine is running and i remove the oil filler cap there is no air blowing out that it spits oil on my hand. I know the engine works on compression and expansion of air / fuel mixtures but i believe that the pressure should not be releasing up through the engine head as vigoursly but like i said i have no experience with VAG engines!!

Johntegr

ocelot83 wrote: »

thanks for the replies

I have no experience with audi / voltwagan engines but i have a mitsubishi colt and when the engine is running and i remove the oil filler cap there is no air blowing out that it spits oil on my hand. I know the engine works on compression and expansion of air / fuel mixtures but i believe that the pressure should not be releasing up through the engine head as vigoursly but like i said i have no experience with VAG engines!!

If it's physically spitting oil at idle then I'd look into if there's too much oil in it or a problem with the crank case.

ocelot83

I dipped the oil before i started the car and the oil level was just below the max mark with the car on level ground. I am more concerned with the strong draft blowing out from the engine head when the oil filler cap is removed.

George Dalton

What you describe is normal for one of those engines.

dr.fuzzenstein

AFAIK it could be a case of valve stem seals, piston rings or cylinder bore worn.
A car should not blow out of the oil filler cap like an old steam train.
I'd check with a specialist if it is indeed normal, but I wouldn't accept the say-so of some people off the internet and I'd include myself in that.
What's the mileage? Does the oil look OK? Is there service history?
If mileage is high and reply to a question on service history is met with "ah sure, be grand now, always done on the button by me mate John-Joe, sucking daesel, be grand now, she's a flier", don't walk, away, RUN!!!!!!!!!!!

Tea drinker

It's vastly more likely a something in the combustion chamber rather than valve stems.
Sticking or worn rings, worn bores or pistons, take your pick.

But a certain amount of blow by is perfectly normal. Most important is the PCV system is working well to recycle the pressure back into the air intake. If this is blocked more pressure will escape from the oil filler cap than would otherwise, and the abnormal pressure build up tends to blow various seals around the engine then.

Pottler

probably just a blocked breather valve as said before, but could also be knackered rings. First one is no biggie, second might be nasty.

L-M

George Dalton wrote: »

What you describe is normal for one of those engines.

This is what you need to listen to, OP.

MugMugs

Limerick man wrote: »

George Dalton wrote: »

What you describe is normal for one of those engines.

This is what you need to listen to, OP.

+1

OP. George is a specialist of VAG engines.

slapstick

i thought blowing from the oil filler neck was a bad thing , shouldn`t you feel a pulse like rythem of sucking and blowing ? was told years ago a piece of light paper placed over the filler neck should vibrate with the engine pulses and not just get blown away from the neck as it would if there is only blowing without the sucking .... if that makes sense ?
i`d be keen to hear some more well informed opinions on this for future reference

Bobo78

+3

lostboy

tried this once with a 4 stroke scooter engine, it shot a spray of oil in my face and accross the drive way, never again, i later learned it was normal for such a thing to happen.

piston

On OHC engines where you can actually see the camshaft (many engines put have "spashguard" under the oil cap), it definitely wouldn't be unusual to have a little oil sparked out of the oil cap when you remove it as the rotating camshaft is throwing it. It's years since I looked under the bonnet of TDI VAG, I can't recall if the camshaft is exposed or not.

Any oil or fumes being blown out of the dipstick tube is an entirely different matter.