7 Steps To Clean The Crankcase Ventilation System Of A Car Engine

Steps To Clean The Crankcase Ventilation System Of A Car Engine

To discourage oil from being thrown into the combustion chambers and to prevent any chance of fire, modern crankcase ventilation systems incorporate an oil separator and a valve or flame trap.

In time, these restrictors can become clogged with deposits carried by the oily fumes, and if they are not unblocked, the resulting pressure build-up causes oil leaks.

Most carmakers recommend cleaning the breather assembly at 10,000-12,000-mile intervals.

As most cars now have a closed or semi-closed breathing system that includes a spring-loaded ventilation valve, these types are dealt with here.

STEP 1

Remove the oil filler cap. If it has ventilation holes and contains a gauze filter, rinse it in paraffin and shake off the surplus before refitting it.

STEP 2

On caps without ventilation holes, check that the rubber sealing ring is sound and able to make an airtight joint. If the ring is damaged, fit a new cap.

STEP 3

Locate the ventilation valve, on most cars, it is at one end of the ventilation hose joining the crankcase to the inlet manifold or carburetor air cleaner.

STEP 4

Remove the valve assembly and clean it with an old paintbrush dipped in paraffin. Test its action by gently pressing the valve into the housing; it should move easily and freely against slight spring pressure. If it has a sticky action that cannot be improved by cleaning, fit a new valve. This may not be necessary as some valves can be dismantled after removing a circlip at the end.

STEP 5

Disc-shaped valves, mounted on the inlet manifold, must also be dismantled for cleaning. These valves have a spring-loaded diaphragm inside, and a top cover held by a spring clip. Move the clip aside, remove the cover and lift out the diaphragm and spring underneath. Clean all parts and reassemble in reverse order.

STEP 6

Undo the hoses and check them for blockages. To clean a sludged-up hose, make a pull-through by hooking the end of a length of stiff wire around a small piece of cloth. Thread the wire through the hose and use it to draw through the cloth.

STEP 7

On reassembly, make sure that all hoses fit firmly and make an airtight joint. Air leaks cause erratic engine idling.