How Does an Oil Catch Can Work?

Knowing the inner workings of a vehicle comes with its set of benefits. You know the risks associated with potential issues, understand the causes, and can quickly fix things DIY-style. It is especially true when we consider the heart of the vehicle—the engine. And some degree of knowledge is helpful when dealing with direct injection engines and oil catch cans.

What Is a Direct Injection Engine?

One must first learn the function of direct injection engine technology to understand the use of an oil catch can. Direct injection technology is a fuel delivery system used primarily in modern-day cars with diesel and gas engines. In direct injection engines, instead of the fuel/air mixture entering the cylinders through intake valves, an injector sprays fuel directly into the combustion chamber. Direct injection technology provides better fuel economy and more power based on the application. It can bump up the torque delivery by as much as 50 percent. 

What Are Examples of Vehicles Using a Direct Injection Engine?

Many vehicles employ direction injection technology which is also referred to as gasoline direct injection (GDI) or direct fuel injection. Initially, direct injection technology was more closely associated with diesel-powered vehicles such as the TDI lineup from Volkswagen and Audi. Although TDI is the moniker for the group’s diesel models, the “D” is not for “diesel” but “direct”. Here, TDI stands for turbocharged direct injection. Direct injection is employed beyond diesel vehicles and is leveraged in Mazda’s Skyactiv engine technology. For example, both the Mazda3 and Mazda CX-90 feature direct injection engines. 

What Is an Oil Catch Can? 

If you have a direct injection motor, it might be helpful to know about the oil catch can. Oil catch cans are simple devices that greatly benefit direct injection engines. The oil catch cans prevent oil and other contaminants from causing a buildup of debris inside the engine’s intake manifold harming horsepower and fuel economy. 

The oil catch can plugs into a hose that runs from the top of the engine’s crankshaft to the engine’s intake manifold. The hose releases pressure, allowing oil and debris from the crankshaft into the engine intake manifold. 

What Is the Use of an Oil Catch Can?

The oil catch can is an oil/air separator. It can separate the oil droplets from the air circulating from the engine breather and then through the intake system. The internal combustion systems are imperfect, and the pressure in the combustion chamber sometimes finds its way into the oil pan or the crankcase. It is called the positive crankcase pressure. The pressure must escape through a ventilation system called the positive crankcase ventilation valve. 

The characteristics that keep the engine friction low also do not let the piston rings create a perfect seal against the cylinder wall. Oil droplets are vaporized when the pressurized air mixes with the spinning crankshaft and other engine components. 

The vaporized oil contains contaminants that are produced by combustion. The vaporized oil particles escape through the positive crankcase ventilation valves. The vaporized oil is redirected back into the engine’s intake system and processed through the emission control devices into the exhaust system. The process is necessary to reduce air pollution and abide by the guidelines but hurts the intake system. 

Why Is the Oil Catch Mandatory for Direct Injection Engines? 

An oil catch can is necessary for direct injection engines. Whereas port-injected engines act as a cleanser by spraying fuel into the intake manifold to wash off the oil and reduce debris build-up, direct-injection engines shoot fuel directly into the cylinder. Thus, direct injection engines lack a buffer or filter to prevent the debris from getting in and creating a build-up. This is where the oil catch can comes into play. Working like a filter, the oil catch can plugs into the hose line to catch the debris before it can reach the engine’s intake manifold. 

How Does an Oil Catch Can Work?

The oil catch can supplements the breather hose between the PCV and the engine’s intake system. The breather hose from the PCV is disconnected from the air intake and is replaced or directly connected to the catch can input.

The air travels from the bottom of the catch can through a tube, back to the top of the oil catch can, and towards the outlet passing through a filter. A hose comes from the outlet that completes the circuit and reconnects to the air intake port. When the air passes through the catch can filter, it traps the oil particles and pools them together into larger droplets before falling to the catch can’s bottom. 

The catch cans are fitted with a drain plug to eradicate the oil catchment periodically. Under usual conditions, there is no need to maintain the catch cans between regular service intervals. However, some recommend checking the catch can every 500 miles or when you conduct an oil change. 

Do Only Direct Injection Engine Vehicles Use an Oil Catch Can?

While direct injection engine vehicles are manufactured with oil catch cans, tuners have been adding oil catch cans to non-direct injection engine vehicles for years to increase horsepower and fuel economy. Oil catch cans may make sense for drivers who have already added other modifications such as turbochargers or superchargers as well as for drivers who frequently operate the vehicle at a high RPM (rotations per minute).

Although an oil catch can offer benefits, it is not without its concerns. When voluntarily adding an oil catch can to your non-direct injection engine vehicle, it is believed to be an alteration to your vehicle’s positive crankcase ventilation (PCV) system. So, before installing this upgrade, you should be aware that an oil catch can installation will likely compromise your vehicle’s warranty. Similarly, if you live in a state with strict emission system testing regulations, modifying your vehicle with an oil catch can may also make you subject to fines. 

Summary

As direct injection engine technology has become more common, so have oil catch cans. If you are adding an oil catch can as a modification, understand warranty and emission regulations impacts before proceeding. There are many brands and models available depending on your needs for flow, filtration, and mounting location. To find the right oil catch can, try talking with your mechanic or doing some research. 

Matt Yantakosol is a lifelong automotive enthusiast and former consultant focused on the consumer aspect of the industry. He has traveled to New York, Detroit, Chicago, L.A., Paris, Geneva, Frankfurt, and Tokyo Auto Shows to track and observe the newest industry innovations. In addition to JDPower.com, Matt's writing has appeared on Pcarmarket.com.

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