The Nissan CA18DET is a small yet mighty engine. While if can perform extremely well in normal driving conditions, it can really suffer during prolonged high RPM use.
This is due to excess crankcase pressure not being able to escape quick enough through the factory block breather, hindering oil from draining back into the sump.
This issue is much worse in a badly maintained engine as the block breather is commonly known to clog - causing the cylinder block to struggle venting crankcase pressure to the cylinder head, where it is finally passed out of the breather.
This coupled with the CA18DET’s phenominal factory oil pump causes excess oil to build up in the top of the cylinder head, usually being expelled through the breathers. Many times this will cause people to fill their catch cans in just minutes of driving, leading to dangerously low oil levels.
The head drain kit aims to allow for proper ventilation between the engine block and cylinder head, while providing two additional points of drainage for the cylinder head to stop it from flooding and being expelled through the valve cover breathers.
Why is the head drain kit designed for the exhaust side, rather than the intake side?
This question is simple yet often overlooked. The engines crankshaft spins clockwise - as it spins, it creates strong winds within the crankcase. With the drain and vent ports being on the exhaust side, the airflow created by the crankshaft helps “pull” air through the lines where as if fitted on the intake side, this would push air flow into and up the head drain lines - effectively fighting the oil from draining!