Tier 4 engines run with closed crankcase ventilation (CCV) systems. Instead of venting blow-by gases into the atmosphere, the gases are routed through an oil separator (crankcase filter) and back into the intake. It's an emissions requirement, but neglecting this $50 filter will destroy a$20,000 engine in a spectacular fashion.
As piston rings wear, combustion blow-by increases, carrying hot, oily vapor into the crankcase. The CCV filter separates the oil and returns it to the pan, while the clean air goes to the intake. Over thousands of hours, the filter media becomes saturated and plugs with sludge.
When the CCV filter plugs, the crankcase has no way to vent its pressure. As the engine runs, the internal pressure climbs to 10, 20, or even 30 PSI. The weakest point in the engine block is the rear main seal. The extreme internal pressure physically blows the rubber lip of the rear main seal completely out of its housing groove. In a matter of seconds, the engine pumps its entire oil capacity out onto the ground through the gap where the seal used to be. If the operator doesn't notice the oil pressure gauge drop to zero instantly, the engine spins a bearing and locks up. A simple, neglected crankcase breather filter turns into a catastrophic, total engine failure.
