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Old 01-12-2012, 01:45 PM   #20 (permalink)
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Originally Posted by mwebb View Post
PCV "catch can"
no engine should ever need a PCV Catch can , if yours does , that is one indication that your engine has bad piston rings or a sloppy seal at the turbo center bearing
the piston rings may just be frozen with carbon in the lands because the engine has been operated with
poor quality oil for many moons
I understand your concerns regarding the PCV system, but I have a few follow-up questions, statements, and a respectful difference of opinion in some situations...

In the case of Josh8loop's TDI, it appears that a reasonable collection system was designed to remove a nominal amount of oil from the turbo bearing seal and then from the crankcase. If a pressure guage were to be applied to the capillary tube, I expect a very small reading of negligible, intermittent pressure. I would imagine that losing small amount of oil is typical for a turbo, with the speed, temperature, and pressure of the application? Also, turbochargers in consumer applications tend to fail at the 100K mile mark (on the average) without proper cooldown during the life of the component. Timed idling before shutdown (not advised for FE) or light driving before shutdown, has demonstrated a preservation approach to turbo longevity, as you probably know.

To demonstrate the amount of emissions from this system on a larger scale, take a look at a large, rear-engined tour bus. Since a closed PCV system is not required for large vehicle applications, a vent tube generally exhausts the vent directly into the atmosphere. If one looks underneath while the vehicle is at idle, the downward-pointed tube is often clearly visible, and vents quite a bit of contaminants. If left stationary and idle for a while, a greasy/oily spot can be seen on the pavement where this tube vents.

These vehicles are designed to run 100's of thousands of miles, and typically vent a considerable amount when relatively new. Would diesel engines have more blow-by due to the higher compression and a larger supply of oil? In our small, closed PCV systems, we simply want to condense and collect the discharge before it can potentially degrade downstream components or senselessly be burned and released into our air.

My personal goal (and likelly that of others) is to remove airborne pollutants, contaminants, and whatever blow-by occurs in normal engine operation -- and especially as engines accumulate more hours and inevitably wear out their piston rings. The system has existed for a reason (for decades), and can account for significant air quality issues if not maintained. For those strapped for cash, it can be an inexpensive addition to prevent costly and inefficient operation later.

Further, despite the closed nature of the sytem, I would expect condensation and warm-up evaporation to be a factor on cold starts and/or humid days, increasing the vapor amount.

I applaud Josh's collection of intercooler contaminants, through carefully constructing a relatively non-invasive setup. Whether or not the turbo is significantly leaking, collecting over 5 oz. of comtanimants over 50K miles establishes the "every little bit helps" rule, and thus far, has not been reported to be a detriment.

As for me, I plan to continue my usual maintenance routine, involving the use of high-quality oil / filter changes, Seafoam cleanse directly into the intake, and the catch can. So far, 50K miles later, it sill runs smoothly and efficiently at 160K total miles.

“If we knew what we were doing, it wouldn't be called research” ― Albert Einstein

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