PCV System...School Me!

[Kotta390]

I understand what the principle is behind the PCV system. The reason I bring up this topic is because apparently I don't understand enough about it. IE; I have a catch can on my truck and I do 90% highway driving literally. I also do the very occasional "spirited" driving as well. My concern is I thought the PCV system stays mostly closed during light throttle and thus there shouldn't be much oil in the catch can over the course of "X" miles driven compared to someone who drives with a heavier foot or more in town driving then I do because of the heavier load on the engine. The issue I am having is compared to others, from what I read, is that I am accumulating MUCH more oil in the catch can then I would presume be there. In the course of about 1000miles give or take 100, I notice a pattern that my catch can is about half full. From what I can tell I shouldn't have a half full can of oil until roughly 1500-2000 miles of driving. Whether this is true or not I still feel like I am accumulating more oil than I should.


Can someone explain how the PCV system works under light and heavy throttle and also am I to worry about this situation or is this 100% normal?

 

[Kotta390]

?Nobody?

 

[GP4L]

Traditional PCV's is nothing more than a simple check-ball type valve, and is opened by intake manifold vacuum. So, it's almost always open. Some are spring assisted, meaning they'll only open under higher vacuum (like engine braking/idle). Some are solenoid controlled for whatever reason.

The purpose is to apply negative pressure on the crankcase. As the pistons reciprocate, air is rapidly moved around, and keeping that negative pressure (almost) constantly applied prevents the pistons from having to fight pressure underneath them when they are traveling from TDC to BDC. Blow-by on power strokes also create pressure inside the crankcase. The reason why crankcase ventilation isn't just simply vented to the atmosphere (allowing the "pressure" in the crankcase to escape) from the factory is 100% because of emissions. Keeping it the engine crankcase "closed" and forcing the engine to burn whatever oil / combustion vapor that gets pushed/sucked out, gets sent through the catalytic converter(s) just like the rest of the exhaust gasses.

If your catch can is in series with the ENTIRE crankcase ventilation system, it will fill up - as it should. How fast or slow it fills is subjective.

 

[Casper]

I understand what the principle is behind the PCV system. The reason I bring up this topic is because apparently I don't understand enough about it. IE; I have a catch can on my truck and I do 90% highway driving literally. I also do the very occasional "spirited" driving as well. My concern is I thought the PCV system stays mostly closed during light throttle and thus there shouldn't be much oil in the catch can over the course of "X" miles driven compared to someone who drives with a heavier foot or more in town driving then I do because of the heavier load on the engine. The issue I am having is compared to others, from what I read, is that I am accumulating MUCH more oil in the catch can then I would presume be there. In the course of about 1000miles give or take 100, I notice a pattern that my catch can is about half full. From what I can tell I shouldn't have a half full can of oil until roughly 1500-2000 miles of driving. Whether this is true or not I still feel like I am accumulating more oil than I should.


Can someone explain how the PCV system works under light and heavy throttle and also am I to worry about this situation or is this 100% normal?

^^^ X2.
Your case sounds like more than average for blow-by based accumulation in your catch can, but if you aren't finding yourself a quart low before every oil change, its probably no big deal. RAM has a ridiculous allowance for oil-use as still being normal so you wont get any help from the dealership unless you're emptying the sump between oil changes (exaggeration, but not by much).

 

[charonblk07]

The PCV valve is vacuum controlled, it's closed at idle and fully open at the lowest vacuum. Light throttle is actually where you will generate the most flow through the PCV since you still have higher vacuum, if that's where you spend most of your driving then you will generate more flow through the PCV. There won't be a lot of blow unless the engine's not up to temp and the rings are sealing properly. Under heavy throttle you have less vacuum but you generate a lot more blow by which again is flowing through the PCV.

Some engines have more, some have less, a lot is dependent on the driving done as well. As long as you're not losing more than a quart per oil change then you're fine.

 

[Kotta390]

Yeah I figured it was a little more than average but the truck runs like a bat out of hell and the last time I checked the oil it was good. So only under high vacuum the PCV is open. Which really means that my extensive highway driving is probably the root cause for this. If I were a betting man and I drove my truck in the city over the same amount of miles I bet the catch can wouldn't fill up as much as it does now.

 

[SlowRoller]

Tons of variables involved as to how much 'material' you will collect in the can.

Amount of blow-by generated by the engine is one. Don't confuse the amount of flow through the PCV system with amount of blow-by produced by the engine,,, (So your Truck runs like a 'bat outta hell' eh? I can see why your 5.7 would be exposed to conditions that generate more blow-by than ole Slowrollers 5.7,,, )

Short trips vs. long trips. (emissions/condensation-related)

'New' oil vs oil with a few thousand miles already on it as well as different brands/types of oil. (NOACK rating related)

Outdoor temps/mounting location of can. (2 more condensation-related factors)

And of course,,,, type of can,,,,

 

[Kotta390]

Tons of variables involved as to how much 'material' you will collect in the can.

Amount of blow-by generated by the engine is one. Don't confuse the amount of flow through the PCV system with amount of blow-by produced by the engine,,, (So your Truck runs like a 'bat outta hell' eh? I can see why your 5.7 would be exposed to conditions that generate more blow-by than ole Slowrollers 5.7,,, )

Short trips vs. long trips. (emissions/condensation-related)

'New' oil vs oil with a few thousand miles already on it as well as different brands/types of oil. (NOACK rating related)

Outdoor temps/mounting location of can. (2 more condensation-related factors)

And of course,,,, type of can,,,,

Haha "exposed to conditions that generate more blow-by then ole Slowrollers 5.7" That made me laugh out loud!! Don't get me wrong I like stomping on it every great once in awhile, but I have an issue with fuel mileage to an extent and do not like to see anything under 20mpg to the tank on each fill. I understand the many principles, but it just seems to be a little more material collected than others. I was just curious as to why this might be. Either way it isn't losing enough to be a concern as of yet. I definitely will keep my eye on this as time goes on.

 

[Burla]

PCV is nothing to worry about, if yours gets clogged up your engine will create it's own

 

[SlowRoller]

Yes, Ole Slowrollers cylinder pressures generally stay a lot lower than you younger guys!!! (It's part of getting old! LMAO!!!)

Keep an eye on the can, but more importantly, keep an eye on the dipstick,,,, What 'looks like a lot' in the can is typically barely noticeable on the stick. If the stick reads good, doesn't reveal excessive consumption,,, all is good!

 

[Kotta390]

Haha very true Burla!!

Slow roller, I typically check my engine oil every 1500 miles, and it always looks good but you do have a point about what may look like a lot in the can generally doesn't affect oil level all that much.

 

[blackbetty14]

You should get the most in the catch can during high vacuum driving, highway, light throttle and downhill. I actually get 1/2 to 3/4 of my catch can filled every 500-1000 miles or so depending on my driving. While u would think its a lot it's not, prob like 6-8oz. Still the oil consumption of these hemis are rediculous and the most I've seen with any car I've owned. Just imagine all the oil getting into the intake.

 

[R.L.K.]

I understand what the principle is behind the PCV system. The reason I bring up this topic is because apparently I don't understand enough about it. IE; I have a catch can on my truck and I do 90% highway driving literally. I also do the very occasional "spirited" driving as well. My concern is I thought the PCV system stays mostly closed during light throttle and thus there shouldn't be much oil in the catch can over the course of "X" miles driven compared to someone who drives with a heavier foot or more in town driving then I do because of the heavier load on the engine. The issue I am having is compared to others, from what I read, is that I am accumulating MUCH more oil in the catch can then I would presume be there. In the course of about 1000miles give or take 100, I notice a pattern that my catch can is about half full. From what I can tell I shouldn't have a half full can of oil until roughly 1500-2000 miles of driving. Whether this is true or not I still feel like I am accumulating more oil than I should.


Can someone explain how the PCV system works under light and heavy throttle and also am I to worry about this situation or

www.oilcatchcan.com

 

[SlowRoller]

Engines with more blow-by can produce higher amounts of 'crudola/combustion by-products/vapors, etc' than engines with lesser amounts of blow -by.

Some of these blow-by components are what's caught with a catch can.

You get the most blow-by under hard acceleration (low vacuum - high cylinder pressures - "richer" A/F mix)

Just cruising down the road (high vacuum - ~lower~ cylinder pressures - "leaner" A/F mix) does not create as much blow-by.

{'New' engines vs 'worn out' engines as well as N/A engines vs. forced induction engines have different levels of blow-by as well.)

Although not normally seen in N/A 'OEM' engines in good mechanical condition, during hard acceleration, some engines will produce more blow-by than what can be accommodated by what we normally think of as the 'PCV system' and actually force the extra crank case vapors out the PCV 'make-up' line . (PCV make-up line is the air line normally supplying clean filtered air to the crankcase. Its the line running from the intake filter housing to the drivers side valve cover on our 5.7's)

 

[RodRam]

Easy fix....get a bigger can, J/k i added a moroso can to mine recently have not checked it yet but did check flow at idle by opening the drain valve while at idle and it had full flow of air sounded like. I wouldn't worry about it, mopar designed the motor to run fine without a CC and give a 100k warranty, just cant imagine if all this was such a issue there would not be a CC as standard equipment but i see where it can keep the engine cleaner so why not so i jumped on the Crazy train with everyone else

 

[GP4L]

Does anybody make an air/oil separator? Basically a catch can that allows accumulated oil to drain back into the crankcase. Used to use these on built Subaru's all the time...
Crawford Air/Oil Separator (08+ WRX / STi) - MAPerformance

 

[Kotta390]

Easy fix....get a bigger can, J/k i added a moroso can to mine recently have not checked it yet but did check flow at idle by opening the drain valve while at idle and it had full flow of air sounded like. I wouldn't worry about it, mopar designed the motor to run fine without a CC and give a 100k warranty, just cant imagine if all this was such a issue there would not be a CC as standard equipment but i see where it can keep the engine cleaner so why not so i jumped on the Crazy train with everyone else

Because it would cost more in production, BUT the MAIN reason is the consumers as a whole are not used to adding the maintenance of a catch can to the list of already poor maintenance that they do in the first place. LOL

 

[Kotta390]

Does anybody make an air/oil separator? Basically a catch can that allows accumulated oil to drain back into the crankcase. Used to use these on built Subaru's all the time...
Crawford Air/Oil Separator (08+ WRX / STi) - MAPerformance

Unless you are making some SERIOUS blow by where it will literally guzzle through a quart every 1000 miles or something to that extreme, I would never want to recycle the oil that came through the PCV. You do realize that is oil, mixed with fuel and putting it back in your crank case overtime will start to cause issues with gunk in the crank case.

 

[RodRam]

Does anybody make an air/oil separator? Basically a catch can that allows accumulated oil to drain back into the crankcase. Used to use these on built Subaru's all the time...
Crawford Air/Oil Separator (08+ WRX / STi) - MAPerformance

You dont ever want that kind of setup, you dont just get oil in the CC, its got some fuel and water in it too.

 

[powderbrad]

mines maybe 1/2-3/4 full throughout an oil change