Direct Injection (DI) motors are great, they make more power while using less fuel. How? The fuel injector is located in the cylinder head and spray fuel directly into the combustion chamber allowing for a more precise and atomized application of fuel. In Mulit-Port Injection (MPI) systems the fuel injector is located in the intake manifold behind the intake valve. Both air coming into the motor and fuel both must flow into the cylinder head around the intake valve.
Now the problem. DI motors have a horrible habit of having the intake valve getting caked up with nasty carbon deposits, which leads to lower performance because less air can get in, and in some case the valve won't fully close. Why? Well motors have a PCV (Positive Crankcase Valve) system, where hot oily vapors from the crank case are sucked back up into the air intake where it can be burnt. It is much friendlier for the environment to burn this oily vapor vs. just expelling it to the atmosphere. So MPI motors have the injector spraying fuel directly at the intake valves, it basically washes off the intake valves. Since the fuel injector for DI motors is located in the cylinder head, there is nothing to clean off the intake valves. Thus over time (as low as 40,000) miles the the intake valves become all caked up with black carbon. Worse than an old man who eats bacon and hamburgers every day!
Two things can help make this issue better. First one is running a quality oil that is made for direct injection motors. What makes an oil better for DI motors? The oil has less tendency to evaporate. Less evaporation means less oil to be sucked into the intake system, thus carbon build up. Second is install a catch can with baffling. The catch can goes inline with the tube carries the crank case vapors to the air intake. The purpose of the catch can is to get those oil vapors to turn into oil droplets, and those oil droplets collect in the bottom of the catch can, so the air the motor is ingesting has less oil to form carbon deposits.
Ok great problem solved! Right? Well, unless you live in an area were it gets real cold. That oily vapor coming out of the crank case into the catch can then into the intake system, it contains a lot of moisture. That moisture can freeze and restrict the flow out of the crank case. Worst possible scenario now, is that crank case pressure gets to high, and the vapor finds the next easiest place to escape, which often time is the crank shaft main seal. If the crankshaft main seal goes, the whole transmission and clutch/flywheel need to come out! Some people remove their crank case catch can during the winter and return to the stock setup to avoid that issue, but now the problem of carbon build up returns.
My solution! I purchased a catch can made specifically for my car, that has really short hoses. Some kits have multiple feet of hose which is just more area for the lines to get frozen and clogged. Next, I remembered that the Volkswagen MK3 GTI VR6 has these little heating elements in the crank case lines. I was able to find two of them in my parts pile, with the harnesses, I wired them up to be on with ignition. Now both crank case vapor going into and out of the catch can must pass through the heating element.
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