Crankcase Breather System - Maintenance

Here is a diagram :

Air is pulled into the engine by the force of the pistons (natural asperation). Through :

1. Air filter
2. Air flow meter (/ECU)
3. Corrugated sleeve
4. Through the throttle body.
And into the intake manifold for use in the combustion process.

When the 'ignition' stage occurs within the 4-stroke cycle, a large explosion between the cylinder head and the piston head takes place. Some of the 'live' and 'waste' gasses may pass the piston rings and end up in the crankcase.

Due to these fumes, there can be a large amount of generated pressure in the crankcase. These 'fumes' contribute to a large proportion of a car's emissions. Not very long ago, these fumes were allowed to escape into the atmosphere... but now they are recirculated back into the inlet manifold and reburnt in the 4-stroke cycle.

The oil filler cap (yes, Mr. Olio) has two separate sections within it. This allows the fumes to be separated from the oil in the crankcase - and be put back into the inlet manifold by pipe 7, the Crankcase Ventillation Pipe.

Where the pipe meets the Corrugated Sleeve (3) there is a 'flame retard apature'. This is basically a machined hole of correct size to allow the correct pressure through the system.

Begin by removing the Crankcase Breather pipe from the oil filler tube by removing screw 1. Pull the pipe off the tube. Some oil may come out, put some rag in the tube end to stop it covering the whole engine bay!

Remove screw 2 which is inside the oil filler.

This removes the oil filler from the tube (there SHOULD be a screw retainer on this. Mine doesn't have one, if yours doesn't, then be bloody careful not to drop the screw inside the engine!!!!).

Now remove the filler, revealing this :

Mop up the oil on the top of the tube (yes the bit still on the car!). This may contain little particles, try to remove all these too - make it look nice and clean.

Now take a container (I've used the base of a Coke bottle) and put some parrafin in it. Don't fill it right up, as we'll be dipping the oil cap into it :

Now place the oil cap into the parrafin, try to clean out the metal gauze on the base of the cap with a paintbrush.

Now we will clean out the Crankcase Breather pipe and apature.

Firstly remove the other end of the pipe that was connected to the oil cap :

Remove the clamp NEAREST THE CORRUGATED SLEEVE. This will allow you to remove the apature too :

Once the pipe is off of the car, you can remove the other clamp to allow access to the pipe and apature separately.

Clean both the pipe and the apature in the parafin.

DRY all the parts throughly before refitting to the car in reverse order.

Please note, outside the UK parafin is known as KEROSENE.

Bobbber
October 2005 - Derbyshire UK
Comment on this article

Comment from Henning : Not every oil filler is attached to the tube with a screw. Mine is attached with a bayonet nut connector which makes it much easier and safer to remove it. This applies to post 1992 cars :