Wednesday, April 18, 2012

Leaky Oil Filler Cap?

Do you have the problem of oil stains around your oil filler cap?

It may not just be a leaky cap that is the problem.

Many have tried replacing the cap without any resolution to the leaking oil through the filler cap.

The problem may be built up pressure within the engine due to a blocked engine breather (crankcase ventilation) air passage.

Leaky filler cap? Or other issues?
The engine releases built up pressure from the evaporated fumes via the crankcase ventilation hole.
This is connected to the engine breather hose that routes these fumes back to the air filter box for combustion again in the engine.

If the engine breather outlet is blocked, pressure built up is unable to escape and thus the only other outlet will be via the oil filler hole, causing the oil to stain the area around the cap.

In most cases, the blockage isn't due to the breather hoses. Because the breather hoses are of diameter 5/8". Carbon and oil gunk couldn't possibly block up such a wide hole.

The more likely suspect will be the plastic strainer of the valve cover [aka cam cover].

Cam cover's plastic strainer leading to ventilation outlet
This plastic cover have an inlet where fumes enter the strainer and exits through to the connective breather outlet, before it connects to the external breather hoses. As seen in the picture above, the inlet for the fumes is small and may get trapped with gunk.

A quick solution will be to blow compressed [clean] air into the cam cover's ventilation outlet with the oil filler cap removed. By blowing, it may dislodge trapped gunk within the strainer and allow the passage to be clean again. With the above method, you do not have to open up the cam cover or any parts of the engine, all that is needed will be to remove the air filter box, disconnect the engine breather hose connecting to the crankcase breather hose and blow compressed air into the hole.

Personally, I recommend the blowing of compressed air to be done whenever each 5000 km or 10000km servicing is due. Prolonged high pressure within the engine may eventually cause the cam cover gasket to leak as well...

Hope you will find this information useful and apply the knowledge the next time you see a oil stains around your oil filler cap.