Oil catch cans, or simply catch cans. You hear about them all the time but not really sure if you need one or what they even do. Let me start by stating that I recommend if you want to aggressively drive your car that you get a catch can as your very first mod. Why?
Catch cans are a preventive device and can also be a “performance” mod. A performance mod?! That might sounds ridiculous, but don’t worry, I’ll explain in a minute.
What does a catch can do?
As the name implies, a catch can catches oil and prevents it from going back into your engine. Wait, what?!3point8 YouTube Channel
Engines have a positive crankcase ventilation system which everyone simply calls the PCV. This system allows the pressure that gets built up in the crankcase to be relieved. It also allows other things like moisture and fumes to be evacuated as well. I won’t get into exactly how this works because that’s not the point here, but it’s important to note that it relies on vacuum from the intake manifold (or a source of vacuum in general).
Most PCV systems will be redirected back into the intake manifold which means anything that escapes from the crank case will end up in your cylinders and this means that you’re burning oil.
Over time this oil will coat the intake manifold, intake valves and the tops of the pistons. Over time this sludge builds up and will kill performance.
Dirty engines are not happy engines. This is where a catch can comes in. A catch can sits between your PCV valve and your intake manifold. Any oil, moisture and other contaminants that would normally come out of the PCV value and go into the intake manifold will now flow into the catch can first, and the job of the catch can is to prevent this crap from going back into your intake.
Catch cans have different designs. Some are just empty cylinders with an inlet and an outlet and nothing else. Some have mesh that only lets air pass while trapping particles, some are baffled and some have a combination of the two.
This is an example of what a catch can does. This oil was collected over a 4 week period of aggressive driving including a track day. If you’re thinking that you are exempt because you have a brand new car, think again. I only had 10,000 miles on the engine when I took this photo.
There seems to be a lot of confusion around catch cans and how to hook them up, but they are very simple devices with very simple installation. The hardest part of installing a catch can is finding a place to mount it.
There are TWO parts to the PCV system, the inlet also called the vent and the outlet, or, the PCV valve. This is why you see the PCV routed to the intake manifold and the vent routed to the intake tubing or the air box – two different parts.
The PCV side needs a catch can weather you’re naturally aspirated or boosted. The vent side, however, may or may not need a catch can depending on your setup. Naturally aspirated cars (in general) don’t need a catch can on the vent side and can usually just run a breather.
Some people get confused because they see oil in the intake tract coming from the vent. This is because at wide open throttle, the air going through the intake passes over the vent tube and creates a type of suction add a sufficiently restrictive intake tract and the issue becomes worse. If you put a breather on the vent, you won’t see any more oil coming from the vent, assuming you have a healthy engine of course. If you do see oil, then you have another issue. If you have an older motor or have issues with your piston rings, you may have excessive blow by at wide open throttle which can force oil out through the vent in which case you would need to add a catch can to the vent side.
For forced induction cars, the PCV valve is closed under boost to prevent pressurizing the crank case, but pressure still builds in the crank case and where does it go? Through the vent. So for boosted cars it’s recommended that you also have a catch can on the vent side in addition to the PCV side even on a healthy motor.
How much should you spend on a catch can?
The cost of a catch can does not determine it’s effectiveness. I’ve used cheap cans I built myself using an oil/water separator for an air compressor with great success. I’ve used $110 cans and had issues. Some people pay upwards of $350 and that’s a personal choice. But, just because it’s more expensive doesn’t mean that it’s better.
However, that doesn’t mean cheap ones are OK to run, either. For example, I bought a basic can from eBay to run on my Chevy Cruze and I kept having problems. Eventually, I took the can apart and found that the even though the fittings were ½” on the outside, the ports were actually only about 5mm on the inside so there was a severe flow restriction. So just do your research, don’t cheap out but also don’t think that you have to buy the most expensive catch can you can find.
What about performance?
As I mentioned, this is one of the first mods anyone should do to their car. Not only is it a preventive maintenance mod, but it can also be a performance mod. That might sound ridiculous, but if you think about it, it makes sense. Hot oil going into your cylinders has the potential to cause knock. When the car detects knock it will cut timing which means you’re losing power to some degree.
Oil build up on the valves will add to flow restriction over time and can cause valves to stick and the oil being burned can cause carbon build up on the piston tops which may cause hot spots, again, causing knock. So, a catch can may not add any power, but it will certainly help keep you from losing the power that you do have.