The "Catch Can" Explained - By Elite Engineering

Elite Engineering · April 17, 2015

With all the talk about Catch Cans, we thought it would be a good idea to combine the information into a smaller thread here.

To better understand the purpose of a good quality PCV Oil Catch Can and why they are important, we need to first understand the purpose of your Stock PCV System:

The PCV (Positive Crankcase Ventilation) system on your engine is designed to regulate and remove fumes from the engine crankcase, and to alleviate crankcase pressure which could cause oil leaks or seal damage. It’s a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine.

During normal operation of an internal combustion engine, there’s a compressed air and fuel mixture inside the combustion chamber that is ignited and as a result, forces the piston down. A small amount of that ignited mixture leaks past the piston rings and ends up in the crankcase.

This leakage is often referred to as “blow-by” (leakage past the piston rings), as well as oil mist. Some of the oil mist and other products settle along the engine intake and over time form a “gunk.” The oil catch can collects the oil mist and condenses the fuel vapors while allowing “cleaner” gases to be passed back into the intake.

If these contaminates are kept inside the combustion chamber, they will eventually make their way into the oil inside the crankcase and cause oil contamination and dilution or make their way back into the intake manifold.

This problem has been documented in many automotive magazines, Car & Driver had an article covering this topic (Carbon Deposits with Direct Injection) There are hundreds of images on the Internet of Carbon Build up on Intake Valves:

http://www.gm-trucks.com/forums/topic/154204-oil-catch-can/?p=1608015

The purpose of a proper oil separating Catch Can is to route these gasses through a baffle system that provides the most contact possible with the outer surface resulting in the oil being trapped and removed from the other gasses that do continue on through the intake and are burnt and consumed. Typically the trapped oil is captured in the bottom of the Catch Can.

If you do your homework, you’ll find a lot of good Catch Cans on the market. You will also find a lot of products that claim to be Catch Cans but have no internal design or baffling to create the optimum amount of pressure drop to pull the oil out of the vapor.

Many Catch Cans on the market are just comprised of an empty container with 2 ports. While that simple design may trap a few oil droplets, a well-engineered Catch Can is designed to condense the oil vapor and trap the oil inside the container.

As I said, there are a lot on the market, go with a company you can trust.

Edited April 17, 2015 by Elite Engineering

LongrangeLauber · April 17, 2015

I will definitely pin this for all to see. Thanks for the explanation!

BuyAmericanIron · April 18, 2015

This is my third Elite catch can. They flat out work with no issues. Great company to deal with and excellent customer service. Attached is a picture of my catch can after only two hundred miles. The truck had 1500 miles when the can was installed.

Stoddard · April 18, 2015

So please prove to me before and after pics of a catch can keeping valves clean...

Bvonscott · April 18, 2015

What happens when that catch can fills all the way up?

BIG THUNDER II · April 18, 2015

What happens when that catch can fills all the way up?

You have to empty it periodically before it fills all the way up.

2007silveradonbs · April 19, 2015

Are there ever any deals or coupons for Elite Cans?

Spurshot · April 19, 2015

You have to empty it periodically before it fills all the way up.

The difference between a "catch can" and an "air/oil separator system", as used on a number of OEM vehicle applications, is the drain back to the sump.

If GM had put a catch can on a vehicle, we'd hear cries of being tossed back into the 20s, when you had to grease the rocker arms before running your engine. A catch can is fine for the race cars and street rods, and even the meticulous street gear head. It's not something you want to forget to service.

I chose to buy a separator type with a drain back to the sump. This is an OEM type product that needs no routine intervention to drain. In addition, it has protection from overpressure with a bypass valve as well as a crankcase pressure regulating valve for supercharged engines. These types of systems are used on numerous OEM installations, including BMWs to large turbo-supercharged diesel truck applications. http://www.grupoherres.com/v3/intro/boletin/mann.pdf

https://www.mann-hummel.com/en/corp/products/crankcase-ventilation/

If you believe all the stuff we're seeing is oil in these pictures posted on this forum, their oil pans would be empty before the OLM change period. The fact is that much of what we're seeing in these pictures is a large quantity of water condensate mixed with oil.

You should research the various products out there and chose for your application, situation, and as importantly, your lifestyle. My lifestyle is to expect to use the truck like GM intended, with a similar maintenance schedule. That doesn't include remembering to drain a catch can. YMMV.

Edited April 19, 2015 by spurshot

Panik · April 25, 2015

Spurshot - would you be willing to post a couple of pics of how you installed your separator? I've been piddling around with the idea and like the price point and what I'm seeing from Mann-Hummel. Any issues with installation or function? Thanks

Elite Engineering · April 25, 2015

Spurshot - would you be willing to post a couple of pics of how you installed your separator? I've been piddling around with the idea and like the price point and what I'm seeing from Mann-Hummel. Any issues with installation or function? Thanks

Look on the bottom of these installation instructions, this is how we connect the Clean-Side Separator.

http://www.eliteengineeringusa.com/content/Catch_Can_Install_Chevy_GMC_2014_5.3L_6.2L_Truck.pdf

kzinge1 · April 27, 2015

I've already installed the Elite Catch Can and am happy with the results so far. How important would it be to add the clean side separator in addition to the can? How much oil gets by with just the can?

surebuttercringe · April 28, 2015

OK, so I'm going to ask the obvious (and maybe stupid) question...

If this is an issue, why aren't catch cans and/or oil/water separators installed from the factory on every vehicle?

LongrangeLauber · April 28, 2015

OK, so I'm going to ask the obvious (and maybe stupid) question...

If this is an issue, why aren't catch cans and/or oil/water separators installed from the factory on every vehicle?

If the manufacturer can clear the powertrain warranty without issue, why bother (from the manufacturer perspective)? These are just to hopefully help us owners who want to extend the life of the engine and keep it as close to a new engine as possible

Spurshot · April 29, 2015

OK, so I'm going to ask the obvious (and maybe stupid) question...

If this is an issue, why aren't catch cans and/or oil/water separators installed from the factory on every vehicle?

Virtually all vehicles have some type of air-oil separator in the PCV system. Most are simple baffle/labyrinth style. Some are very sophisticated. Nearly all will have a drain back to the sump.

I recall a round breather cap style with a hose bib on an early 60's car my father owned. It had baffles and drained back into the rocker cover like the RT and Elite "clean side" caps, but it went to the PCV valve.

The foreign cars seem to have more sophisticated centrifugal or filter type separators. The American engines seem to have the least efficient/effort designs.