The PCV Catch can is more of a preventative measure than an actual gas mileage booster. Here is what it is, how here is how to make one yourself.
PCV tube stands for the Positive Crankcase Ventilation tube (PCV). It's used to vent any pressure built up in the head of the engine, but since we have emissions laws, that venting means that the gasses must be properly burned to prevent excess pollution. This is done by sending the gasses back into the engine through the intake. When this occurs not only will the engine have a pushing pressure, the intake will also have a sucking action working on the tube. This results in a force so great that gasses AND oil will be transferred from the engine and into the intake manifold. In other words, it results in burning oil.
What's bad about burning a little oil? As oil gets sucked in, the throttle body, intake manifold, cold start fuel injector, and T-VIS butterflies develop a thick oily residue which coats everything it touches. When the tiny particles of dust and dirt that make it past the air filter come in contact with that oil, they bond together making a thick sludge. In the most severe cases, this can lead to the complete failure of the T-VIS system when the butterflies get so gunked up they can no longer open and close properly. The bad part about getting the throttle body dirty in particular is that it has sensors within it that contribute to the info the ECU needs to properly run the engine. Those sensors can't operate properly if they're covered in an oily residue. I'm not certain how bad it is for the cold start fuel injector, but I'm fairly certain the injector wasn't designed to operate while covered in crap.
The solution is to clean the throttle body, injectors, and intake manifold periodically to insure that the oil residue is removed, or you can remove the oil BEFORE it enters into the throttle body/intake manifold. This can be done using a PCV catch can.
A PCV catch can lies between in one of two locations. It lies between the PCV valve and the air intake manifold, or between the cylinder head cover and the air intake. I have heard of both of these instances working. Some people install the catch can on both tubes to ensure that no oil is getting through to the throttle body. The PCV catch can filters the air and seperates the oil out of the air. The basic theory behind the catch can is best illustrated here:
There are a few methods of how to construct such a device. It all depends on how many "around the house" objects you want ot use, or how nice you want it to look. The best construction I have seen uses an water filter that is used in air compression tools. They can be found in Home Depot, Lowes, or other hardware stores. One resource recommended Campbell Hausfeld part #MP513810. Any water filter made for air compressors should work.
The first thing to do is to remove the small filter screen inside the filter. It is not needed for our application, and leaving it in could cause a buildup of oil to clog the filter. Next wrap thread lock around the fittings that you will eventually screw onto the filter. When this is done you will either cut the hose you want the filter on and install it at the break in the hose, or you will buy a new hose to prevent damaging your old one. Some people use longer hoses in order to be able to mount the filter on the firewall.
You end product should look like this:
The catch can needs to be cleaned every once in a while, which can be done by unscrewing the glass receptical and pouring out the oil. The frequency at which you are required to empty it depends entirely on your engine and the amount of oil being sent through the filter.
In my experiance, the only way you can keep your engine clean without "rippin it up" is driving them nice lean-burn hwy miles. When you do a lot of "throttling" such as in city stop and go driving, the engine is more apt to enrich the fuel/air mixture.
Then IF you stop(read:turn off engine) and you were running rich, the CC is more coated in fuel than with the more lean-burn hwy mode. That coating slowly forms deposits as the vehicle cools, and later on turns to carbon as the volatile components evaporate.
Another way to keep overly rich fuel out of the CC is to have an O2 that works good (read: a newer 02)
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