There are a few interesting things about the oil breather pipes.
The engine gets hot, there is very little you can do about it, inevitably the oil gets hot too.
We all know that hot oil is a good thing as it flows better and protects the moving parts.
Some parts of the engine get a lot hotter than others, this can boil the oil which then turns into burnt oil vapour. Burnt oil is no longer any good for the engine so while it is still a vapour it is ejected from the engine via the crankcase breather pipes.
To stay within the EU emissions guidelines this vapour cannot be purged into the atmosphere, instead it is channeled either to the air intake manifold or the TIK pipe where it travels through the
engine and is burnt in a normal combustion cycle and ejected from the exhaust.
Lower Breather Pipe
The lower breather pipe connects the crank case to the TIK pipe.
Its main function is to draw in filtered air to replace the air removed through the top breather pipe.
There are occasions when burnt oil vapour will exit through the lower breather
pipe instead due to the check valve on the upper breather closing. If this check
valve is closed for a while, the burnt oil vapour is vented into the TIK pipe where
it is passed into the engine to be burnt in the combustion cycle.
As this pipe is primarily an air intake for the crank case, it is important that if it is
redirected to an oil catch tank that the tank has some type of filter on it. Small crank
case breather filters can be bought from most car shops and places such as Ebay.
If you do not fit a filter, dirty air can be sucked into the crank case.
This dirty air is sucked across the oil in the crank case and the oil will collect the dirt.
This reduces the efficiency of the oil and causes unnecessary wear on other engine parts.
Upper Breather Pipe
The upper breather pipe connects the crank case to the inlet manifold just behind the throttle body.
Because of its location this pipe can experience boost and vaccum created in the inlet manifold.
The vacuum is used to draw the burnt oil vapour through the top breather pipe and into the engine to be burnt, the lower breather pipe replaces the air taken by the upper breather pipe.
When there is a positive pressure in the intake manifold, a small valve located on the
upper breather pipe closes. This stops the boost pressure entering the crankcase.
Boost pressure entering the crank case would be very bad as it would cause oil to be
forced out of the lower breather pipe and into the turbo.
This much oil entering the engine would cause very poor running, black smoke from
the exhaust, high compression, possible bent con rods and possibly a head gasket failure.
Not to mention the loss of oil could cause the engine to seize up completely.
Upper breather pipes replacement can be found here. Change it every 3 years to be safe.
Fit A Catch Tank
This information has been added to and given its own page. See it here.