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Engine guides and mods

Top Breather Pipe Replacement

Failure of the top breather pipe valve can cause excessive oil usage and engine smoke. It's cheap to replace so why not do it before it breaks?

Modification Details

The top (or upper) breather pipe has an important role in the smart engine. It allows burnt oil vapour to be
pulled into the combustion cycle to be burnt. It has a check valve that only allows air to flow from the engine to
the air inlet manifold so when the throttle body closes it creates a vacuum in the pipe which draws the burnt
oil vapour into the engine. When the turbo is creating boost, the valve in the top breather pipe closes.

The problem occurs when the valve becomes faulty. The diaphram in the valve splits which allows boost air
created by the turbo to go back into the engine crank case. This can cause pressure to build up to the point
where the oil dip stick pops out swiftly followed by a fair bit of oil. A loss of oil is obviously bad news.

Unfortunately this is only the best case scenario. 

The oil can also be pushed out of the lower breather pipe which is connected to the TIK pipe.
This would allow a lot of oil to be pumped straight into the turbo, through the intercooler and into
the engine. If a lot of oil gets into the combustion cycle it will increase the compression in the cylinder
and possibly bend a con rod, blow the head gasket or damage the pistons.

So as you can see, it pays to check the upper breather pipe every now and then.

Testing The Valve


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