But what is a catch can and is it illegal to install one in your car? In order to understand what an oil catch can is, you first need to know what oil blow-by is.
During the compression stroke, an immense amount of pressure is built up so much that a small amount of air can escape from around the piston rings.
Among those deposits are carbon, which must be removed. Carbon deposits reduce the efficiency of your engine, causing disruptive shaking during idling and unexpected ignition failures. They also shorten the life of components so you may have to do maintenance more often. No engine works to optimal efficiency with blowby cycling through, and all engines will suffer irreperable damage over time.
That would lead to the conclusion that all engines could potentially benefit from an oil catch can. However, drivers of high-performance vehicles potentially have the most to benefit from the installation of an oil catch can. This is because, for these cars, optimal performance at all times is essential. Also, because of the greater potential for deposit buildup than in older engines, cars with newer gasoline direct injection GDI or direct fuel injection DFI engines especially benefit from oil catch can technology.
Strictly speaking, any car can continue to run without an oil catch can. However, if you do not install one, you have to take other steps to deal with the effects of blowby in your vehicle.
Why does this specifically affect direct-injected engines? Well, in port-injected engines, the fuel being sprayed into the intake works as a cleanser, washing off any oil buildup that might occur. Since direct injection engines shoot fuel directly into the cylinder, there's nothing preventing gunk from building up. An oil catch can acts as a filter, plugging into this hose line to "catch" the contaminants before they can reach the intake.
As Jason Fenske of Engineering Explained shows in this video below, even a budget catch can is better than nothing. The only downsides are figuring out how to mount one under your hood, and remembering to empty it every now and then.
Inside the crankcase, you have the crank which is turning in the oil pan which is full of oil. This keeps it properly lubricated. PCV or positive crankcase ventilation is necessary to ensure there isn't a build up of pressure in the crankcase. This would cause the crankcase to possibly crack under the pressure and create a huge mess of oil on the street.
So the PCV system removes the pressure from the crankcase and reverts it back through the intake tract via crank case vents. It will also contain a very small amount of oil as well since there is so much in the oil pan at a high temperature.
This air and oil mixture is then entered somewhere after the intake system, passes through the intercooler if you car is turbo or supercharged and then re-enters the combustion chamber cylinder through your intake valves to be re-burned. The oil will actually coat everything on its way back to the combustion chamber. It will develop in the intercooler, boost hoses, intake manifold and intake valves. Just on the other side of these valves is where the combustion is taking place where the temperatures are extremely high.
This is what actually causes the oil to solidify on the valves. With the oil passing through the intercooler, it can actually coat the cooling fins which will hinder the intercooler's ability to cool the air therefore lowering the efficiency. The caking on intake valves is only a problem with direct injection engines. For all other engines that use port injection, the gas is introduced before the combustion chamber which means it flows over the intake valves and enter the combustion chamber premixed with the air.
This action of the fuel flowing over the intake valves actually cleans the valves from any oil that may already be on there.
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