What does the crankcase vent filter do? The crankcase vent filter is used on high performance engines such as race car? though it is Œćused on older models of vehicles as well. Inside the engin? small amounts of combustion gases push by the piston in the cylinder and enter the crankcas? or the bottom end of the engine. These gases create a positive pressure inside the crankcas? which needs ventilation. Positive crankcase pressure robs the engine of power as the pistons have to fight against that pressure when performing each down stroke?A breather tube is mounted at the top of the crankcase in the engine block that releases the positive pressure into the environment or into the intake to cleanly burn them before they enter the atmosphere. The breather tube contains a port or elbow at some point along its route where the crankcase vent filter is installed. How do you know you need the crankcase vent filter replaced? There is oil on engine Engine oil seals leaking due to clogged filter Poor Engine performance How is the crankcase vent filter replaced by a mobile mechanic? Filter is confirmed faulty The defective crankcase filter is removed by opening the air filter housin? disconnecting the vent hose and removing the clip New filter is installed and clipped in Air filter housing is closed and system is tested How important is having your crankcase vent filter replaced? The crankcase vent filter allows excess pressure to push out of the system without carrying oil particles or other messy contaminants with the gases. It also prevents any debris or dirt from entering the crankcase if negative pressure occur? such as engine cooldown. If the crankcase vent filter is clogge? the excess positive pressure inside the crankcase can blow out engine oil seals. If the crankcase vent filter isnt in plac? dirt can enter the crankcase and plug oil galleries or contaminate the oi? which can cause lasting engine damage.