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[Abiton]

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on a different forum i was told to see if the breethers were clear that if you place your hand over the filler hole there should be a slight vacuum, if it sucks hard then the breethers are blocked - on my car there is a slight bit of positive pressure, so i am guessing this is a good sign.
any more idears ?

many thanks to all.

This doesn't seem very logical. First you (or the other forum) say a bit of negative pressure is good, then they say too much is blocked breathers?  Surely that would be super-unblocked breathers? Then you say a bit of positive pressure is good?  :-?

In my understanding, the breather system is designed to prevent positive (above atmospheric) pressure of crankcase fumes in the crankcase and camcover(s), by using inlet manifold 'suck' to cancel out blow-by.   If there isn't enough suck, the inlet manifold is not sufficiently connected via the breather system to the bits it's trying to reduce the pressure of. 

One thing no-one seems to mention is that older, more worn engines are likely to have more blow-by, and the breather system may not have been designed with enough 'headroom' to cope.  :-/

[Andy H]

...
on a different forum i was told to see if the breethers were clear that if you place your hand over the filler hole there should be a slight vacuum, if it sucks hard then the breethers are blocked - on my car there is a slight bit of positive pressure, so i am guessing this is a good sign.
any more idears ?

many thanks to all.

This doesn't seem very logical. First you (or the other forum) say a bit of negative pressure is good, then they say too much is blocked breathers?  Surely that would be super-unblocked breathers? Then you say a bit of positive pressure is good?  :-?

In my understanding, the breather system is designed to prevent positive (above atmospheric) pressure of crankcase fumes in the crankcase and camcover(s), by using inlet manifold 'suck' to cancel out blow-by.   If there isn't enough suck, the inlet manifold is not sufficiently connected via the breather system to the bits it's trying to reduce the pressure of. 

One thing no-one seems to mention is that older, more worn engines are likely to have more blow-by, and the breather system may not have been designed with enough 'headroom' to cope.  :-/

Yes, but.....
There are two paths for the breathers to suck/blow through.

At idle the throttles are closed and two small ports on the engine side of the throttles suck (through one of the small pipes in the Ecotec cover). Only a small amount of gases are blown past the piston rings at idle so there should be a negative pressure in the crankcase pulling filtered air in through the pair of large breather pipes.

When the the throttles are opened the vacuum reduces in the inlet manifold but lots of clean air is gets sucked in through the bagpipes. Any excess pressure in the crankcase should pass through the two large breather pipes and get sucked into the engine without touching the sides.

The small (idle) breather ports will get blocked first. Once they are blocked then the oily mist that would have gone straight into the inlet manifold at idle has to go through the throttle bodies. On a pre facelift the oil will also get pulled through the ICV & cause it to gum up.

So, in summary, there should be a slight negative pressure at idle. A slight positive pressure is acceptable when the engine is under load.

[Kneepad]

...
on a different forum i was told to see if the breethers were clear that if you place your hand over the filler hole there should be a slight vacuum, if it sucks hard then the breethers are blocked - on my car there is a slight bit of positive pressure, so i am guessing this is a good sign.
any more idears ?

many thanks to all.

When the the throttles are opened the vacuum reduces in the inlet manifold but lots of clean air is gets sucked in through the bagpipes. Any excess pressure in the crankcase should pass through the two large breather pipes and get sucked into the engine without touching the sides.

That version was only available in Scotland.