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post #51 of 57 (permalink) Old 03-12-2017, 11:24 AM
SirDuckferd
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The residue that JBR showed looks like fuel deposits and are fairly normal. What you want to avoid is the tar-like substance that is actually PCV blowby (oil).

If they wanted to do the test properly, they would need to run the car back to back with and without baffling, and also heat the mixture that they got off the car to remove volatiles (oil, water) that is harmless to the engine, leaving the actual amount of "bad" oil. Because even the best of the best oil separators would leave moisture and fuel vapour to bypass it since they are designed to remove oil from the system Putting it in the oven for a few hours would do the trick.

The problem with catch cans are as you said. If they freeze, you're now bypassing your PCV system entirely as the entirety of your blowby will now be pushed into the fresh-air line and directly towards your throttle body. What I have seen in the past is that worst case (which isn't likely), you can either freeze your throttle body in position (which is bad if it's open), or you'll form a giant pool of water in the intake manifold, which can get sucked into the cylinders and that's also not good...

On turbocharged engines with a high/low PCV circuit, what I've noticed is that companies like Ford actually have an additional oil separator that is built into the valve cover. You still have the "pre-separator" installed on the side of the engine block, but a tube from the outlet actually leads into the cylinder head where the fine separator does the most important work.

If you want, a carefully placed filter piece in the pre-separator outlet really close to the PCV might be a good bet (angled so that fluid gathers and then drops). The baffling does a pretty good job though, and this engine doesn't really produce enough power or combustion pressure to cause excessive amounts of blowby in the first place. Along with Mazda's supposed engine calibration with intake valve retard it might be OK? The real test is for someone to show the condition of the valves closer to 100K miles.
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post #52 of 57 (permalink) Old 03-12-2017, 11:56 AM
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Interesting, the 'ole catch can or not debate. I belong to seven car forums, and every one has this same debate, with strong emotions on both sides.

For those of you who are running them and are happy campers, good on you.

For those who choose not do, great, for as Sir Duckferd posted (paraphrasing here), it will take thousands of miles to determine who was right to have one and who in hindsight would now have chosen run one from the beginning.

However, again my personal opinion that there are two other major factors that need to enter this debate, the kind of driving you are doing and whether you have been using Top Tier fuels. I am lucky, living in the country, take lots of long drives where my motor is up to temperature. About half of my mileage last year was road trips (14,000+ miles on four of them). Conversely, I have friends who are not retired, drive their cars 2-3 miles on their work commute, on the weekend running a lot of short errands -- and their motors spend a majority of their trips not even up to temperature. Keeping the valves hot (engine of full operating temp) is one key way to burn off all forms of crap including gasoline vapors. And of course using Top Tier fuels has been repeatedly proven to not only give us better fuel mileage, and using Top Tier fuels also results in cleaner motor insides.

One GM engineer's comment is, I believe, is worth repeating. He is powertrain engineer, works on the 455+ HP Corvette, Camaro and Cadillac's -- many of those motors now in the 640+ HP/640 TQ range, when he sarcastically answered a question of how come GM does not run catch cans (except in the track Z28's), and he said, "don't you think if GM felt it necessary to run a $20 catch can, we would be doing that?" I am guessing that the $20 figure would be GM's actual cost if a catch can were factory installed as part of the assembly line process.

Let the strong opinions on all sides continue, and I bet if I were on seven more car forums, I would fine seven more threads with differences of opinion as to whether catch cans are necessary or not.

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Last edited by Road Trip; 03-12-2017 at 12:07 PM.
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post #53 of 57 (permalink) Old 03-12-2017, 12:36 PM
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Quote:
Originally Posted by SirDuckferd View Post
The residue that JBR showed looks like fuel deposits and are fairly normal. What you want to avoid is the tar-like substance that is actually PCV blowby (oil).

If they wanted to do the test properly, they would need to run the car back to back with and without baffling, and also heat the mixture that they got off the car to remove volatiles (oil, water) that is harmless to the engine, leaving the actual amount of "bad" oil. Because even the best of the best oil separators would leave moisture and fuel vapour to bypass it since they are designed to remove oil from the system Putting it in the oven for a few hours would do the trick.
Those are not fuel deposits. They can't be if those pictures are from a SkyActiv motor.
I'm pretty sure the engineers at Mazda did extensive testing during development of this engine. They are quite aware of this issue and did give special attention to keeping the valves clean. What you are seeing in those pictures is most likely the end result of many short trips without ever bringing the engine up to proper operating temperature for any extended period of time.
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post #54 of 57 (permalink) Old 03-12-2017, 01:41 PM
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More than almost anything (except cheap fuel), driving habits will kill an engine.

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post #55 of 57 (permalink) Old 03-13-2017, 04:07 PM
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Originally Posted by arathol View Post
Those are not fuel deposits. They can't be if those pictures are from a SkyActiv motor.
I'm pretty sure the engineers at Mazda did extensive testing during development of this engine. They are quite aware of this issue and did give special attention to keeping the valves clean. What you are seeing in those pictures is most likely the end result of many short trips without ever bringing the engine up to proper operating temperature for any extended period of time.
Don't forget that this engine runs in pseudo-atkinson mode, due to its variable cam phasers.
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post #56 of 57 (permalink) Old 03-13-2017, 04:18 PM
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Quote:
Originally Posted by Road Trip View Post
Interesting, the 'ole catch can or not debate. I belong to seven car forums, and every one has this same debate, with strong emotions on both sides.

For those of you who are running them and are happy campers, good on you.

For those who choose not do, great, for as Sir Duckferd posted (paraphrasing here), it will take thousands of miles to determine who was right to have one and who in hindsight would now have chosen run one from the beginning.

However, again my personal opinion that there are two other major factors that need to enter this debate, the kind of driving you are doing and whether you have been using Top Tier fuels. I am lucky, living in the country, take lots of long drives where my motor is up to temperature. About half of my mileage last year was road trips (14,000+ miles on four of them). Conversely, I have friends who are not retired, drive their cars 2-3 miles on their work commute, on the weekend running a lot of short errands -- and their motors spend a majority of their trips not even up to temperature. Keeping the valves hot (engine of full operating temp) is one key way to burn off all forms of crap including gasoline vapors. And of course using Top Tier fuels has been repeatedly proven to not only give us better fuel mileage, and using Top Tier fuels also results in cleaner motor insides.

One GM engineer's comment is, I believe, is worth repeating. He is powertrain engineer, works on the 455+ HP Corvette, Camaro and Cadillac's -- many of those motors now in the 640+ HP/640 TQ range, when he sarcastically answered a question of how come GM does not run catch cans (except in the track Z28's), and he said, "don't you think if GM felt it necessary to run a $20 catch can, we would be doing that?" I am guessing that the $20 figure would be GM's actual cost if a catch can were factory installed as part of the assembly line process.

Let the strong opinions on all sides continue, and I bet if I were on seven more car forums, I would fine seven more threads with differences of opinion as to whether catch cans are necessary or not.
In this case, oil quality makes a bigger difference. At least if you're in the US, where our fuel is mostly homogenous except for some additive packs. But generally you're at the mercy of the powertrain engineers and how carefully they tuned their system to work under any condition.

You *do* want to run the engine warm, as this burns off moisture in the oil. One issue that occurred in the past with the Northern areas is that as cars are sitting at the dealership, being moved from one end of the lot to the other in order to plow the lot, you sometimes had engine failures because so much water accumulated in the oil pan from the short run times that it caused slush to clog the oil pickup tube.

It's debatable whether PCV catch cans make a difference in port injected engines, because at that point you're mostly concerned about killing the catalytic converter/doing very poorly in emissions testing (by the way, the cost would be more like a couple of bucks since they integrate these "catch can" systems into the valve cover or internally into the engine). If you're a performance engineer, you'd be worried about certain corners feeding oil directly into the PCV outlet and getting sucked into the engine.

Oil separation has become extremely important since direct injection came out. Even more so in high blowby engines (turbocharged), where they've started resembling science projects with their swirl vortex generators and centrifuges, etc. The thing is though, newer generation engines have already improved this aspect of their engine design, about 20x since the ~2008 time period when the Germans and Koreans found out the hard way that you can't just add direct injection and not consider other aspects of your system design. It's gotten so good that catch cans nowadays are mostly catching fuel and water, not actual oil.
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post #57 of 57 (permalink) Old 03-13-2017, 04:38 PM
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Quote:
Originally Posted by SirDuckferd View Post
Don't forget that this engine runs in pseudo-atkinson mode, due to its variable cam phasers.
Only under specific load conditions, not that it makes a difference. There are no fuel deposits because it is a direct injection motor. There is not enough fuel to either clean the valves or leave deposits on them. What you see in those pictures are valves not getting hot enough to burn off oil deposits. The other pictures of what came out of the catch can show what appears to be mostly oily water that could have been easily burned off.
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