Vauxhall Owners Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
33 Posts
Discussion Starter · #1 ·
Anyone any idea what will be causing vacuum pressure in the rocker box of a 1.6 16v astra (2004) when its running the oil cap is hard to get off as its been sucked into position, also if you pull the dipstick out you can hear the tube sucking, the engine revs go up slightly aswell.
??????????????????
 

·
Registered
Joined
·
1,262 Posts
Re: Vacuum holding oil cap tight

my bro in law when he had my astra with the 1.6 16v was the same i just took it that was how it was ment to be
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #5 ·
Re: Vacuum holding oil cap tight

my bro in law when he had my astra with the 1.6 16v was the same i just took it that was how it was ment to be
Ive checked the air filter and the main inlet pipe inc the air flow meter and there is no blockages and there is still vacuum at the oil cap even with the main pipe off.
Maybe this is as normal, but it just seems strange to me.

It is a twinport engine.
 

·
Registered
Joined
·
6,715 Posts
Re: Vacuum holding oil cap tight

Some engines have a rather aggressive crankcase breather system that's intended to flush any fumes out by having a high level of air passing through, certainly sounds like there may be a partial blockage in the breather hose from between the filter and the upper throttle body area.
May not be used, but with some vehicles it is.
 

·
Registered
Joined
·
17,042 Posts
Re: Vacuum holding oil cap tight

Negative crankcase pressure is a gift I would say as opposed to pressure blowing out of it. I don't know but I will check what it is like on my Calibra x20xev,
 

·
Registered
Joined
·
1,589 Posts
Re: Vacuum holding oil cap tight

I thought the majority of engines are PCV type ?
 

·
Registered
Joined
·
33 Posts
Discussion Starter · #10 ·
Think i have found out whats causing the vacuum, Thought i would update incase anyone else is having problems.
A common fault on Twinport engines is for a breather valve inside the rocker cover to fail, this usually gives symptoms of burning oil due to it getting sucked into the inlet manifold, also causes rough idle speed. Other people with the problem say about a hissing or sucking noise from the dipstick or oil cap. So i am presumming this is whats wrong with this car. I need to make sure though as the breather valve is part of the rocker cover and is around £140 (gulp).
 

·
Registered
Joined
·
4 Posts
I had same problem recently with a 2010 astra 1.6, oil cap being held tight, hissing noise and rough running, rocker cover has built in pcv valve, when it fails you get vacuum in cylinder head, bought new rocker cover and gasket (around £40 on ebay), all probs went away.
 
1 - 12 of 12 Posts
Top