5 Best Oil Catch Can & Buyers Guide (2020)

An oil catch can is just another step that isn't necessary, but it can certainly help you prevent your pistons or valves from getting dirty, so something that could be worthwhile doing.

Important things which need to know about the oil catch can

Now, no matter what you call them - oil separator, catch can, AOS, they are all designed to do the same thing, catch and collect the oily vapor produced during combustion before being rerouted back into your intake track, which can cause a number of issues.

Oil evaporation may occur for a variety of reasons, but in particular it may be due to poor-quality lubricant that will evaporate at operating temperatures. The oil combustion products will settle on the intake manifold, throttle, idling valve, polluting some internal parts of the motor and making the engine a whole mess.

First of all, we need a better understanding of a couple of important things, blowby, and of course PCV, which is short for positive crankcase ventilation.

Oil Catch Can

Well, the catch can simply put is simpler. Most of them basically just have an inlet and an outlet and it's literally a regular can. There doesn't necessarily have to be anything in it, so the idea is, if you have that PCV that's coming from your crankcase or your valve cover and you put it on the inlet, then it has to move through a couple hard bands, then it changes pressures as it goes from the small line of the inlet to a large volume of the can and then it is compressed again through a small line of the outlet and will constantly remove oil vapor and stuff to drop out. Then on the outlet that goes straight into your inlet of the engine.

So, that is a positive vent, because when you're on boost, you're actually pulling vacuum through your turbo inlet and actively pulling pressure out of the crankcase and cylinder heads. This leads to moving that oil vapor and in such out of your crankcase and cylinder heads. This how works a regular catch can without any resistance, without filters. Simple as that. If you`re looking something like this, you should definitely check a Ryanstar Oil Catch Can in our list.

You can certainly have a catch can that is a little bit more elaborate than just be simple can. So the example of that, is a Mishimoto Oil Catch Can. It is still a simple can, so whatever is caught will be collected in the can, but there are a couple filter elements to prevent anything that is caught from going back into the inlet of the engine. Sure to say, it is going to improve the effectiveness for a little bit cheaper price than for a oil separator.

One more difference between oil catch can and oil separator is that you do have to monitor your can and empty it periodically if you want to make sure it doesn't fill up all the way, otherwise you're gonna be sucking oil back through the system.

Air-Oil Separator (AOS)

So, what then is air-oil separator (AOS)? Basically, it is exactly the same as a catch can, but it has a lot more pieces to it. The biggest difference is twofold. One is an oil separator has a lot more baffles in the body of it to prevent or to fully separate any oil and oil vapor from the air, before it goes back into the inlet of the engine. So, whatever is pulled in, is only going to be an air, there's not going to be any oil vapor.

On the other part, this has a return. It means, that if ever any liquid or like will be caught in the reservoir of the separator will be put back into the engine, while catch cans are just sealed unit. So, whatever the catch cans are absorbing it just sits in there, so you don't have to monitor this, empty it or check your oil levels, so this is pretty much a “set it and forget it” kind of product.

Another cool thing is it routes coolant through the housing to help heat up the oil back to engine temps, because PCV oil that's caught tends to froth and foam up, so the cooling heating up helps prevent that.

Blowby

So, let's talk blowby. This is the result of the combustion event that drives the piston in any internal combustion engine. You've got your gas, you've got your air, which is then ignited by your spark plug, and they go boom, right, and most of the remnants of that explosion are pushed out through the exhaust valve as, well, exhaust. However, there is a small amount of this leftover gas mixture that doesn't get expelled and is essentially pulled down past the rings and into the crankcase, hence the term blowby. And this blowby is typically increased in forced induction applications as those cylinder pressures are increased.

PCV

Now this blowby, or vapor, needs a place to escape, right. And up until the early 1960s it would either sneak past gaskets or seals or out of what was called a road draft tube at the time, which essentially was really the first iteration of proper crankcase ventilation. However, this road draft tube, was discovered, wasn't necessarily ideal as it led to a bunch of pollution and a strong odor at idle, and if that tube ever got clogged, well, then that pressure would force all of that vapor through various seals or gaskets, which would lead to leaks, and obviously that's not a good thing.

Now that led to the implementation of PCV systems, or positive crankcase ventilation, on most new cars by the year 1964. Now this was essentially the first vehicle emissions control device and it's been on cars pretty much ever since.

So what does positive crankcase ventilation mean or do? Well, instead of dumping all of that unburnt vapor, or blowby, back into the atmosphere, it was then rerouted or recycled back into the engine through a PCV valve and a series of hoses to be burned off through the combustion process all over again.

If the car’s mileage approaches 35-50k thousand miles, it is recommended to change the oil supply tube (it often cokes and prevents the oil from flowing into the turbocharger) together with the turbocharger. If this is not done, then the turbine shaft may be damaged and the bearings will be in trouble.

Change your catch can at the same time you change your engine oil, so you don`t forget it.

This all sounds fine and dandy, right? Well, not exactly. You see, all of that unburnt fuel and oil mixture that does get rerouted back into your engine does so, typically, through the intake manifold so it can be re-ingested by your engine. The problem is, that stuff is oily. It's sticky. It's gross, right? And over time, it collects in areas that aren't necessarily ideal, including the intake manifold itself along with the backside of your intake valves, that can lead to a little thing called valve coking, which can turn into a big thing over time.

Valve coking

Now valve coking is the extreme buildup or deposits of this junk on the backside of your intake valves, which can lead to poor performance, rough idle, misfires, and even more.

So we know the issue, but how does an oil catch can or separator essentially fix this issue? Well, easy. The separator's going to install in line with your PCV system and it's gonna isolate all that oily gunk and collect it into an easy-to-empty container while still allowing that nice, fresh, clean air to pass through and not disrupt the PCV functionality.

By cleaning the air returned to the inlet system, the separator-catch can reduces the amount of carbon deposits on the throttle, candles, valves and inlet manifold, This means that the engine maintains optimum efficiency and does not lose power for a long time.

There are two of the most common options for separating crankcase gases from oil.

This may be ordinary filter elements using a fabric or metal filter and cyclone oil separators, so-called centrifugal separators. Thanks to the separator, the engine intake system remains clean, which is particularly important in vehicles with high mileage, as well as those with turbocharged engines and tuning-modifications.

In the first option, the oil is separated from the gases by the resistance of synthetic fabric or fine metal wire (the internal filter element needs to be replaced or washed over time).

While the centrifugal oil separator separates (sorry, haha) lubricant from gases as follows: when passing through the device gases and oil suspension in them are like «spinning», exposed to the centrifugal force. Thanks to this centrifugal force, the oil settles on the walls and flows back into the internal combustion engine. Here the oil is finally separated from the gases.

The cyclone oil divider is equipped with a special valve which restricts the discharge in the engine crankcase, since heavy discharge can damage the engine dust and its rubber seals.

Since oil separator is a more intricate and more convenient solution it is going to be a bit more pricey than a catch can. At the end of the day if you do a lot of performance driving or you just like the convenience factor - an AOS is definitely a worthwhile investment.

Otherwise, if you want to save some money and you're okay with monitoring the levels of the catch can and making sure it gets empty when it needs to - this can also can be a cheap effective solution.

It's all up to you.

Resources:

1. How to Fix Engine Oil Blow‐By,** **wikihow
2. Here’s How an Oil Catch Can Works, And Why You Might Want One, roadandtrack
3. How Does a Baffled Catch Can Work and Why Do I Need One?, ecstuning