Car enthusiasts have quite a few traits in common. They’re DIY people. They love a clean car in good repair. They favor high-performance engines and/or keen handling. And many of them add options to their car.
The oil catch can is just one option that some enthusiasts have pondered.
In this article, we will ask some serious questions about just what it does, whether it is absolutely necessary, and what are some of the problems you may find yourself dealing with one.
What is Blow-By?
Catch cans are used to manage blow by. This refers to that mixture of fuel, air and combustion products that escape past the piston rings into the engine’s crankcase.
It is during the compression stroke that a small amount of the fuel-air mixture will be pushed across the piston rings. And during the subsequent power stroke a small amount of those combustion products will leak past the rings as well.
New or recently rebuilt engines will always have a greater flow rate of blow by into the crankcase than older engines with worn rings. In either case blow by happens, and vehicle manufacturers equip crankcase ventilation systems to control that so it does not create heightened pressure in the crankcase.
How Does Crankcase Ventilation Work?
Crankcase ventilation forms another part of your car’s emission control system. This system is often referred to as the PCV (positive crankcase ventilation) system.
It employs vent ports (usually two) in the crankcase connected by metal and/or flexible tubing with ports in the engine intake system. The “blow-by” enters these ports and flows with the fuel-air mixture to intake and is burned.
Why Can Blow-by Be a Problem?
Blow-by is a combination of a vapor and a fine spray of microscopic droplets or aerosols. Once this foul mixture enters the intake system it flows past each open intake valve and down into the combustion chambers. It is this trip past the intake valves where problems may occur.
As the blow-by passes the valves it impinges on each valve and does not entirely remove itself so that it leaves behind a small amount of the blow-by products (these are crusty deposits) on each valve.
For a port injected engine or an engine with a carburetor(s) this event is no great disaster but for a direct injected engine this can cause very expensive problems over time.
Port Injected and Carbureted Engines
In these engines the fuel is mixed in the inlet air before the intake valves; as the fuel-rich charge flows past the intake valves both cleaning each and partially or completely removing the blow-by products that would like to collect there; a good thing for this kind of engine.
Direct Injected Engines
Direct-injected engines (GDI or gas direct injected) are quite different beasts to port-injected or carbureted engines. GDI uses fuel injectors inside of the combustion chambers. Fuel is pumped (literally sprayed) at high pressure right into the combustion chambers during the compression stroke.
For these engines, no fuel ever passes over the intake valves and so no beneficial cleaning of the valves takes place. This type of fuel injection system can allow build up of blow-by products on the intake valves.
These deposits will be ‘baked’ onto the hot valve surfaces, and with a lot of miles (generally 50,000 or more), the deposits can restrict air flow into the combustion chambers. Engine performance will begin to suffer because of this flow restriction.
As more and more car builders adopt gas direct injection, special efforts require by the engine designers to implement effective management of blow-by.
Managing Blow-by
For some newer cars, the crankcase ventilation systems incorporate internal features that allow some or most of the blow-by to condense or coalesce into a liquid state, which is then drained back into the crankcase by the system.
Very little of the liquid products in this blow-by mixture will then get into the intake system and foul the intake valves. Unfortunately, not all cars on the road today have that type of PCV system.
What Is an Oil Catch Can & What Does It Do?
It should be obvious by now how blow-by can adversely affect the intake valves of many cars. What can be done to help protect against this potential problem? Oil catch cans are the answer.
There are several different styles of catch cans available. While different in subtle ways, these all basically have the same features.
The can itself will have ports for both inlet and outlet, and sometimes more than one of each. There will be porting to allow draining, either with an on-off valve, or by allowing the lower part of the can to be removed for drainage. A catch can kit will include installation parts such as a mounting bracket for the can plus all the hoses, fittings, clamps, fasteners and installation instructions.
Following the instructions, the can may be plumbed into the crankcase venting system with the supplied hoses. With the engine running, the crankcase vapors will flow through it, and condensation of vapors and conversion of aerosols to a liquid state will be trapped in the catch can. This liquid must be occasionally drained and properly discarded.
Important: If this drainage is not done periodically, the catch can will fill to overflowing, with the entrapped fluid pouring right back
How Much Does an Oil Catch Can Cost?
Catch can kits can range in cost from as little at $25 and upwards to around $500.
How Often Should a Catch Can be Emptied?
There’s no single mileage number that would answer this question. If you install a catch can on your car, use the can manufacturer’s recommendations for periodic drainage. If you don’t have the can manufacturer’s recommendation, check the level of fluid in the catch can within the first 250 to 500 miles of driving and drain the fluid at that time.
Use this same drain interval for several cycles until you develop confidence that the can can go longer prior to being emptied. Tying this initial ‘short’ change interval with actual experience avoids going unduly long and having the can overflow into the engine’s intake system.
What Vehicles Can Benefit From a Catch Can?
It should be obvious from our preceding discussion that any vehicle with a GDI engine should benefit from having an oil catch can installed.
Vehicles with port fuel injection or that use a carburetors can also benefit to some degree where the flow of crankcase blow-by back into the engine will upset proper fuel-air mixtures and will result in less-efficient operation of an engine with less-generated power as a result.
Does an Oil Catch Can Add Horsepower?
The answer to this question is, possibly, yes. Crankcase blow-by fed directly to the intake system of any engine can adversely affect the power output of an engine by diluting the fuel-air mixture. Less fuel-air mixture goes into producing power due to this dilution.
Avoidance of a portion of this dilution by removing a portion of the products of blow-by may improve engine power and fuel economy in some engines.
Are Catch Cans Universal?
In general, the answer to this question is no.
While the same style of catch can might be of the universal type for many engines, the entire kit that would include a mounting bracket for the can, vent hoses and fittings, and various fasteners will tend to make each catch can kit specific for each particular make and model of automobile.
Single Valve vs. Dual Valve Catch Cans
It should also be noted that your particular vehicle’s engine may require either a single or a dual valve catch can configuration.
Dual valve catch cans (which may also include internal check valves) are commonly fit to engines that also have a turbo or supercharger.
Such an engine adds the complication of crankcase venting into an intake system that will be pressurized in certain modes of operation. Such catch can kits would relate to normally aspirated engines in a negative way.
Where Should the Catch Can Be Installed?
Catch can kits for specific vehicles will provide a recommended location for the can installation. This location will be such that you can access the can for easy periodic draining.
The can location and tubing should not interfere with other routine maintenance work; it shouldn’t infringe on linkages, belts, hot exhaust manifolds, electrical cables or other hoses routed around the engine compartment.
Once the catch can is installed, save the OEM hoses and/or tubing including all clamps, supports as applicable. Take photos of the OEM hoses and connections as a record relative to how the OEM parts were installed. You may need to properly reinstall the factory parts at some time in the future.
Are Catch Cans Illegal?
Generally it will be illegal to modify the like positive crankcase venting (PCV) system on any passenger vehicle since this is also a required part of the federally-mandated emissions control system and it would seem that adding an oil catch can would be a violation.
No aspects of catch can performance that would make the emissions control system inoperative would be possible, of course.
But, one thing that might be in question would the requirement to service the oil catch can frequently (i.e., periodically drain it). Emissions control systems are supposed to require no service for 100,000 miles of driving.
If your state has an annual emissions or vehicle inspection, the modifications you have made with an oil catch can installation might be noted and you could fail that inspection. If in doubt, contacting your state’s Department of Motor Vehicles for advice on this point would be a good idea.
Will It Void My Warranty?
Common sense would tell us that there are no features or characteristics of a catch can installation that ought to put your car’s warranty in jeopardy. If, however, you wrongly install such device by going against the manufacturer’s instructions, suddenly you could stop proper crankcase venting from taking place.
The result could be over-pressurizing the crankcase, premature seal failures, excessive oil consumption and/or possibly various other problems.
Or your inadvertent failure to drain the catch can resulting in it overflowing into the engine’s intake system could easily lead to serious mechanical trouble. Such problems, if presented to your dealer with the catch can package still in place, would surely yield no warranty coverage.
Warranty questions then should be directed to your dealer’s service department prior to the installation of an oil catch can kit.
For you who have any doubts relative to your DIY capability regarding such an installation, the services of a reputable high performance auto shop experienced with your model vehicle should be strongly suggested.
Cautions Before Buying a Catch Can Kit
Before you purchase one of the many oil catch can kits that are available, here’s some further advice to make sure you get the best one for your vehicle.
#1. Download Instructions.
If at all possible, download the installation instructions for the catch can that you are considering buying. With the instructions you can see if you want to perform the installation yourself or find another qualified machine to do so.
#2. Avoid Kits That Require Altering Existing PCV System.
Once you assess the receipt of those instructions, look at how the kit interfaces with your engine. Review this carefully because some caution is in order. Here’s why…
The engineers that designed the engine in your car know far more about how that engine functions than any aftermarket supply company. If the catch can kit instructions have you changing any aspect of the existing PCV system in order to install their kit, avoid buying that kit.
For instance, if a manufacturer’s instructions tell you to block off one or more PCV ports in order to install their kit, use of that particular kit is probably not a good idea. Here’s why. The designers provided the features on your engine for specific reasons.
To tamper with those features in any way could have adverse effects upon your engine. Such tampering could make your warranty void. And tampering and changing the specific features of the ATP or emissions control of yours as we discussed earlier, is illegal.
What Should I Do When I Sell the Car?
You’ve installed a catch can on your car and it’s performed flawlessly for several years. Now you’re selling or trading in the car. Here’s the issue. Will the next owner be diligent enough to perform the periodic draining of the catch can?
The answer here is that you have no way to insure that this maintenance step will be reliably undertaken. As also stated earlier, failure to catch and not performing this service could lead to untold problems.
Here the only likely way out is to remove the catch can and all other associated parts before selling or trading in the vehicle. Restore the PCV system hoses, clamps etc. to OEM condition. If you took charts on that prior to installation, this will be an easy enough process.
Returning everything to factory state is the best way to assure yourself of no future liability or concern with respect to the oil catch can system.