Does your classic engine need an oil catch can?
As emissions restrictions have become evermore strict in automotive engines, unintended consequences have popped up as a result. One such problem is the buildup of oil and contaminants on the intake side of the intake valves, mainly on vehicles that use direct fuel injection. Where is this oil coming from and how do you keep your valves clean? A catch can might be the answer. Engineering Explained has a video dissecting how this inexpensive aftermarket piece can help save owners some trouble, and some money.
With the tightening of emissions controls in the late 1960s, manufacturers began utilizing positive crankcase ventilation systems in place of the previously used road draft tube. This new PCV system pulled any vapors from the crankcase into the intake manifold to be burned as part of combustion. The vapors include oil mist, fuel, and other contaminants that might be pushed past the piston rings but have not yet settled into the oil.
These fumes were simply vented to atmosphere by the old road draft tube system, but that was deemed unacceptable for emissions regulators. More advanced versions of the PCV system have developed, but since the intake air in these systems carries fuel, which is a solvent, the intake valves rarely exhibit any buildup in a good running engine.
Enter direct injection, which takes the fuel out of the intake charge and instead sprays the proper amount of fuel directly into the combustion chamber after the intake valve closes. No fuel to clean the intake valve means the leftover crankcase vapors deposit there. In order to clean the valves, one has to disassemble the engine to the point where the valves can be accessed—not an afternoon job.
As a result, the aftermarket came to the rescue with an item called the catch can. Though it is a small and simple design, the catch can holds mighty powers when it comes to removing contaminants from the intake charge. The crankcase vent air is run through the catch can, which uses baffles or filters to separate the oil from the air, before continuing to the intake manifold.
Once the catch can fills, you’ll have to drain it as a part of regular maintenance. In cold climates especially, water vapor can condense in a catch can and freeze, stopping airflow or damaging the system. During the winter, then, you’ll want to either disconnect the catch can or regularly drain it to avoid freezing.
Older naturally-aspirated engines might not require this piece of modern tech, but if you want to keep the throttle plates of a carburetor or keep the intake manifold cleaner, it is a great piece to install on any engine since there is virtually no downside.