Engine Blow By and Oil Catch Cans - Everything You Need To Know

What is engine blow-by? What is a Catch Can and why is it important? A complete and thorough video explaining the what, where and how of engine blow-by, Catch Can's (PCV Oil Separator)...
What is an Oil Catch Can and do you need one for your engine?
Oil Catch Cans (PCV Oil Separators) are essential for modern common rail direct injection diesel and even some gasoline engines running an EGR (Exhaust Gas Recirculation) systems. PCV or blow-by gases are the additional gases produced by an internal combustion engine during the compression and combustion strokes. Some unburnt & exhaust gases escape past the piston rings and into the crankcase. These gases then have to be vented in order for the pressure in the crankcase to be relieved otherwise they can be known to damage gaskets and seals. In older style engines, the blow-by was just simply vented to atmosphere. However, this changed due to emission regulations. (Blow-by gases typically consist of: water, unburnt fuel, engine oil, exhaust gas and more harmful pollutants.) Today, the blow-by gasses are simply directed back into the air intake of the engine (usually just before the turbocharger). This allows the blow-by gases to be burnt off during combustion. However, with the ever tightening emission regulations, most modern diesel engines are fitted with EGR systems which recirculates some of the exhaust gasses back into the air intake. This then mixes with the blow-by gases and will start to coat the turbocharger, intercooler, air intake manifold, head and valves with oily mist residue. This will then harden (carbonise) and cake over time. Eventually, the carbon will build up that much the engine will suffocate (due to lack of fresh air) compromising performance, fuel economy and longevity.
A good quality Oil Catch Can simply filters (separates) the oily mist from the blow-by before it enters the air intake. This prevents or reduces the likeliness of carbon building up in the engine air intake. An Oil Catch Can is an inexpensive, preventative means to extend the life of your engine.
Beware of cheap Oil Catch Cans. There are only a few good quality catch cans available on the market of which this is one of them.
*Correction: Port injection applies to gasoline/petrol engines only, not diesel engines. Diesel engines with indirect injection have a pre-combustion chamber and therefore fuel cannot wash over the valves... Thank you to those who correctly pointed this out.

[@andrewgibson1991]

This is a total diesel education in a video love it cheers

[@NJSInstructional]

Cheers, thank you!

[@qubadmalik1]

Loved your no nonsense approach and simple explanations without slot of mumbo jumbo like some other people. Thanks for uploading.

[@NJSInstructional]

Glad it was helpful!

[@jaimemarun2841]

Quality of the oil is very important to reduce the blow-by. There are oils with very high volatility (NOACK TEST). In order to reduce blow-by select an oil with a maximum volatility (noack test of 7%.

[@dwayne1655]

Wow what a great video, very well explained and simple to understand. Well done

[@NJSInstructional]

Glad you liked it!

[@joeyjones6638]

Great video mate well explained 👍👍👍👍

[@NJSInstructional]

Thanks 👍

[@truckgotstuck]

Great video.

[@MrJorgvankleef]

good video 👍

[@zeushaider7426]

This is cool thanks NJS

[@PatrickAllen]

Thank you for this fantastic video! I have a hard time not using the torque on my subie sti. But i guess i should let the rpms climb without boosting much if i understood you right? Or just get a air oil separator. Thanks again

[@kenww776]

Excellent explanation!

[@NJSInstructional]

Glad it was helpful!

[@tylersawyer1442]

Thank you

[@sureshthampi7709]

Hi, the product shown is meant for the NPR range of Isuzu trucks. Is it working well in your MUX or Dmax and able to handle the flow rates of the ventilation gases at different speeds/torque ranges effectively? Has the absence of a crankcase pressure regulating valve (like in Provent) in this product impacted you? Can you show how you've mounted it? Thanks.

[@Nick-sd7um]

Subbed. Best and easiest explanations of 4wd diesel related info I've come across. Thank you.

[@NJSInstructional]

Cheers, thank you!

[@joeblowjohnny2297]

My old school chevy 350 has blowby on 1 cylinder . Where do I installed the catch can ? Is it between the pvc inlet hose and the exit to the air cleaner housing ?

[@zeushaider7426]

Do u have an suv/ a 4x4, if you do can u make videos about it? That’s njs

[@LilKing420s]

@NJSInstructional, Great general explanation of how a catch can works. As I am trying to build a DIY setup for a particular vehicle I have a question regarding the size of hose/fittings used in the PCV/catch can system. The catch can in this video seems to have an inlet and outlet that is considerably larger diameter than the diameter of the factory PCV hose. My question then is, how does this size change affect the flow and pressure of the gases within the system? Does it even have any affect? I have scoured the internet for days seeking this information and have found nothing talking about this and thought you might be able to answer such a question or at least point me to someone who could. I thank you ahead of time for any help in this matter.

[@NJSInstructional]

Thank you. You can use reducing elbows/fittings to connect to the engine's blow-by OUT port (on the rocker cover) and turbo blow-by IN port. This way you maintain the diameter of the hosing used for the Catch Can up until the IN/OUT ports. As long as you don't go smaller in diameter than the engine's blow-by IN/OUT ports it should be OK. Remember, the blow-by IN port (just before the turbo) will be under a negative pressure (vacuum) as the turbo will suck the blow-by air in (whether this is from the Catch Can or the standard PCV set-up). You can also check out the Oz Isuzu forum to see how others have plumbed / installed this Isuzu Catch Can in their DMax/MU-X (www.ozisuzu.com.au). Cheers.

[@carlodonnell146]

would it do any good to install a catch can on a 2001 v8 Dodge Ram gasoline engine just o be sure that no oil is getting into the plenum?

[@anthony.grisan]

the catch can is the first addition to my prado.

[@PJ-ee5mc]

This is a great video. Many thanks. I am trying to find a solution for my two 1991 Hino Turbo diesel boat engines but they are 3.83 liter (or 234 cubic inch displacement) so I worry that they may be too big for the part that you are demonstrating here. Although some of the info that a reader pasted below suggested that they are also used on Isuzu's 6 cylinder engine, the 6HK1. Can you offer any further tips for a suitable part or confirm that this one would still work with a 3.8 liter engine? Thanks again!

[@NJSInstructional]

Hi Clinton, yes, this should work on a 3.8L engine.

[@PJ-ee5mc]

​@@NJSInstructional : Thank you for your reply. With some of these older diesel engines they simply vent the blow-by with a hose pointed down into the hull, like on my 1991 boat with twin Hino motors. What doesn't stick to the floor just vaporizes and much of that gets sucked through the air filter eventually and into the motor through the turbo. We don't really have a proper 'intake' for these gases like the kind we have on our newer trucks as in your demonstration. I wonder if its okay to connect the separator's output (now that the blow-by has been cleaned) directly through the air filter itself for a more positive connection. I use K&N filters on my motors and I was thinking of installing a barbed fitting at the end of the filter to accommodate the separator's outlet hose. This would also create a little vacuum which might also be beneficial.

[@TheMahasski]

I have a 2006 isuzu fvr straight truck with a isuzu 7.8l engine with blow by...will a catch can work for me...thanks

[@AndrewSparkfish]

Blocked the egr on my 06 Hilux many years ago, am wondering if i would be on half a mil kms if i had gasses causing a crud build up....

[@QUIKENs2000]

Is it better if i get a breather tank for zr2 or catch can ?

[@christianmong-hansen1835]

Can the oil and vapours also cause knock and bad performance in high hp engines ?

[@maciekperkunert8716]

Witam czy ten produkt zmniejszy ciśnienie?

[@kevinoneill41]

You never talked about the ring gap of the piston. Ring gap is the distance between the two ends of the piston ring as the engine, and piston heat up do does the rings the metal in the ring expands the rings expand closing the ring gap. But the manufacturer mathematically figures this distance out so the rings never touch. So there is always a gap in the rings allowing gas to pass on through to the crankcase. In the 6.4 Ford diesel that gap is quite large as the back two cylinders are flooded with fuel to heat the exhaust to extreme temperatures to attempt to burn clean the soot collected in the DPF. In that time fuel and gasses pass through the ring gap and into the crankcase and engine cavity. The excess fuel mixes with the oil diluting the viscosity of the oil causing the oil to not do its job fully and in so causes premature we are and early engine failure. Also adding to excessive blowby. Putting pressure on deals and gaskets causing oil leaks and failures this has caused catastrophic failure. Remedy deleted the process

[@candylaria5414]

Can’t blow-by be reduced if not cured completely?

[@richardgraham65]

Thanks for the video. I am a bit confused by this (Direct Injection Diesel) Durely it would be better to eliminate the filthy carbon from the EGR going back into the intake, and acutally allow the oil vapour to get recirculated? At least it would provide some upper lubrication, whereas the EGR just pumps filthy exhaust back into the motor - Also, if the EGR is a requirement, why not route it back into the intake before the air filter?

[@NJSInstructional]

Hi Richard, good questions. Even before EGR was introduced, blow-by was already being recirculated back in the engine intake and wasn't a problem. It definitely does provide some lubrication but also can coat the turbo, intercooler etc. with oil. Some engine manufacturers have designed this system (i.e. PCV system) well and others not so much. However, with the introduction of EGR, combining the recirculated exhaust with the oily mist of the blow-by, it can form carbon deposits... If the blow-by was recirculated prior to the air intake, it would then quickly coat the air filter element with oil and block / restrict air flow. Hence, it is always plumbed in afterwards, usually just prior to the turbo. Hope this clarifies. Cheers.

[@richardgraham65]

@@NJSInstructional Thanks for the reply, I added a reduction plate to reduce my EGR and it seems to be helping keep things clean (reduced not blocked) I also vleaned out my intercooler (70,000KM) and it didn't ammount to even a spoonfull of oil. I wonder would it make sense to have some sort of aftermarket kit (Direct injection, not port or combined) that could work like the old Scott Oiler that used to put a drip of oil on motorbike chains constantly - Something that could add a drop of lube / 2 stroke into the inlet manifold... Probably not good for emissions though. Cheers!

[@ismaelcarrillo3956]

@@NJSInstructional I caught that also. "Before the air fiter".

[@Abowhuntersjourney]

So in theory my 1kz-te prado (pre common rail) really wont need an oil seperator ? Forgive my ignorance

[@DimoS...]

Mate I have a corolla ts 1.8 192hp 2zzge is it normal when i open the oil filler cap that air comes out without smoke? or does it have to suck air in? (On running engine of course)

[@NJSInstructional]

Yes, if you open the oil filler cap the air/smoke that comes out is called blow-by, a little bit is quite normal.

[@broshyim3054]

Lc 200 use catch can good or bad

[@buzz7927]

What you thoughts on Toyota when they say fitting a catch can will void a warranty on a new vehicle. do you wait for warranty to expire before fitting.?

[@NJSInstructional]

Good question. Poor installation of Catch Cans (incl. wrong fittings and hose diameters & lengths) can actually be detrimental to the engine. There have been reports of engines blowing main seals / gaskets due to poor installation or poor choice of Catch Cans. It is important to really consider any engine modifications and the pro's and con's of these modifications.

[@candylaria5414]

How do I know if my engine has blowby? What do I look for at the engine bay?

[@waynewilliams5802]

@Candy...baby just let your engine sit an run idle for 5mins. Shut engine off an remove oil cap. If u see smoke u got blow by baby

[@alwaleed31000]

807 2.0 hdi please I want to install my catch can please but I'm not sure where Thank you

[@bbranquinho3133]

did you ever buy an Isuzu oil separator for yourself? How have you been using it?

[@dahaproject3498]

but toyota diesel engine with 2kd series (hilux, hiace) EGR come after intake and throttle body. so it need clean regulary although it has done installed catch can, because it didnt separate 100% oil and air(+carbon)

[@jmoore9806]

What brand catch can is that ?

[@NJSInstructional]

It's a genuine Isuzu Catch Can

[@joeydingel9904]

Come to think of it, you said that oil mist would create gunk in the intake. Because oil mist helps dirt stick in the intake. It is better for it to be in the intske rather inside your engine. Plus it is easier to clean your intake rarher than cleaning inside your engine. This is what car engineers have been telling you guys. Thats why almost all, if not all, cars don't come with OCC. They have studied it and have decades of experience. My friend's turbo was destroyed because of this. They found out that the intake was dry and all the dirt waa stuck inside his turbo. Please try to think about this one

[@funnydubby6401]

I have a question though, if my turbo bearings start to go out, doesnt oil get sucked through towards the compressor hot side and won’t it be the same thing?

[@coosco]

Comon rail or not. Diesel is alwys direct injection

[@Mkiiisoup]

I'm imagining a piston... 00:21 WOW I can see a piston!!! Imaginaaaaaaaaation

[@funfunyo7523]

Why don't manufacturers do it from stock

[@beersintheshed.]

What happens when you don’t service your catch can, I’ll tell you, you blow oil seals.

[@Chuck236mg]

You need to educate yourself on the difference between gas engines and diesel. Because there has never once every been a port injected diesel. All diesels are injected directly into the cylinder or in to a pre-combustion chamber that’s part of then cylinder.