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#4808066 - 07/08/18 01:14 AM Interesting read for all you low NOACK types
SubieRubyRoo Offline


Registered: 05/14/12
Posts: 1232
Loc: Winchester, Indiana
Apologies for the horrible grammar, typos, and just poor wording in some parts of this paper (not mine!). But, from what I gather, oil in PCV system is mainly driven by 4 things, none of which are specifically oil-related: engine speed, piston/piston ring design, cylinder liner temperature, and and oil level (entrainment in the crankcase). NOACK is not mentioned by name but by action (high temperature evaporation of lighter species of engine oil), but it seems to be a very minor component; according to this study, only about 7% of an engine's oil consumption is through the PCV system. In other words, the NOACK of an oil carries almost no effect on the dirtying of the intake side of an engine when compared to the design and use of said engine.

Quote:
it is believed that most of the larger particles are believed to come from the crankcase, while the smaller particles are
from the atomization of the oil by the high speed gas flows under the small clearances in the ring gap.


PCV effects on oil consumption

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#4808069 - 07/08/18 01:30 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
The_Nuke Offline


Registered: 07/21/13
Posts: 313
Loc: D/FW Metroplex
I wonít pretend to know more than the author(s) of that piece, nor will I contradict the points made within it. However, I can attest to the seemingly direct connection between NOACK and oil consumption thru the PCV system in my previous carís engine.

Those engines were notorious for using oil, and whatever the cause for that was, I found quite a bit of it was going thru PCV valve and into the plenum. I also found that if I did my research and ran oils with better NOACK scores, the oil consumption through the PCV would drop proportionally. (I based that judgement on the volume of gunk I would have to empty out of my CC at various intervals on the different oils.)

Maybe the NOACK values didnít have anything to do with what I observed, but whatever it was coincided nicely with the oilsí NOACK...so nicely that they certainly looked to be linked to a lay person like myself.
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#4808101 - 07/08/18 05:38 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
Trav Offline


Registered: 11/20/06
Posts: 19304
Loc: MA, Mittelfranken.de
That may or not be correct but lets call it what it is, its not really evaporation as water does it is loss in the form of oil smoke at high temperature.
The smoke not drawn by the PCV ends up in the engine top end and piston bottoms area then condenses when cooled to form varnish a perfect primer of collecting deposits and sticking this together.
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#4808103 - 07/08/18 05:47 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
wemay Offline


Registered: 04/04/12
Posts: 8994
Loc: Southeast Florida
Where the threshold lies between significant evaporation loss and not is uncertain as it may be vehicle specific, but generally, a lower Noack number is better.
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#4808176 - 07/08/18 08:19 AM Re: Interesting read for all you low NOACK types [Re: wemay]
Bjornviken Online   content


Registered: 12/06/17
Posts: 262
Loc: Finland
Originally Posted By: wemay
Where the threshold lies between significant evaporation loss and not is uncertain as it may be vehicle specific, but generally, a lower Noack number is better.

+1

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#4808184 - 07/08/18 08:35 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
JHZR2 Offline



Registered: 12/14/02
Posts: 41891
Loc: New Jersey
NOACK is simply a test of evaporation loss at a temperature.

In the engine, the temperatures may not be as high for the oil, but they are potentially under vacuum, facilitating the vaporization of the lighter components in the oil.

We wouldnt necessarily care about it if the cold surface that it could condense upon (the intake valve) was washed with solvent. But in DI it isnt. So then we have a beautiful condensing surface for residues to form on.

The mechanisms by which vaporization is facilitated, i.e. high speed gasses, local heating, etc. are all contributors.

But the NOACK consideration and concern is less about "consumption", and much more about the vaporization and condensation.

Quote:
only about 7% of an engine's oil consumption is through the PCV system


That's fine, but its also test, oil, engine design, etc. contingent.

And consumption, again, isnt name of the game here. The question, IMO, is how much vaporized, additized oil is circulating through the system, of which some fraction of components can then recondense on the valves. Its not a lot of material. Vaporization and recondensation may be a much greater quantity than what is consumed, forming deposits.

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#4808201 - 07/08/18 09:07 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
goodtimes Offline


Registered: 12/08/10
Posts: 2908
Loc: california
Back to basics guy. Looked up NOACK test, it's at 250 C or 482 degrees F for one hour.

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#4808375 - 07/08/18 01:30 PM Re: Interesting read for all you low NOACK types [Re: JHZR2]
MolaKule Offline


Registered: 06/05/02
Posts: 19133
Loc: Iowegia - USA
Originally Posted By: JHZR2
NOACK is simply a test of evaporation loss at a temperature.

In the engine, the temperatures may not be as high for the oil, but they are potentially under vacuum, facilitating the vaporization of the lighter components in the oil.

We wouldnt necessarily care about it if the cold surface that it could condense upon (the intake valve) was washed with solvent. But in DI it isnt. So then we have a beautiful condensing surface for residues to form on.

The mechanisms by which vaporization is facilitated, i.e. high speed gasses, local heating, etc. are all contributors.

But the NOACK consideration and concern is less about "consumption", and much more about the vaporization and condensation.

Quote:
only about 7% of an engine's oil consumption is through the PCV system


That's fine, but its also test, oil, engine design, etc. contingent.

And consumption, again, isnt name of the game here. The question, IMO, is how much vaporized, additized oil is circulating through the system, of which some fraction of components can then recondense on the valves. Its not a lot of material. Vaporization and recondensation may be a much greater quantity than what is consumed, forming deposits.



thumbsup thumbsup

I too question the 7% oil consumption figure.

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#4808457 - 07/08/18 03:31 PM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
fdcg27 Offline


Registered: 09/25/09
Posts: 15838
Loc: OH
Okay, but what's the primary cause of increasing consumption with age and hours of operation?
Probably the progressive coking and sticking of the rings.
This process is entirely independent of anything to do with the intake and exhaust processes happening on the other side of the pistons.
Oil must reach the rings both to provide lubrication between them and the cylinder walls and for the rings to make a proper seal. This oil is typically delivered by splash with the oil control ring wiping away the excess.
Which oil is more likely to coke the rings, one that's low in volatility or one with higher volatility?
I may be all wet on this, but I'd personally favor a less volatile oil and would consider it more likely to flow away without leaving hard carbon deposits behind to build up over time.
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#4808571 - 07/08/18 06:33 PM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
JAG Offline


Registered: 10/23/05
Posts: 4887
Loc: Fredericksburg, VA
Intake valves get oil and other substances on them that increase deposits from mostly three sources:
1. PCV flow oil droplets and vapors (this H20-laden, oily concoction is much more degraded than sump oil, and will much more readily form deposits than sump oil)
2. Oil that got past the valve guides
3. Combustion products that got to them from flow reversal out of the combustion chamber.

Port injected engines get fuel on the intake valves which tends to clean them. Obviously, DI engine intake valves donít get that cleaning spray.

More oil does flow through the PCV system when oil volatility increases. The effect this more volatile oil consumption may be minor, and it may even be less oil consumption, depending on the other properties of the oil. However the amount of oil passing through the PCV system is higher and more oil will contact the intake valves. In port injected engines, the fuel will help clean the deposits caused by the oil. In GDI engines, the effect on deposits is much more significant, in my opinion.

The NOACK test is part of all or nearly all oil specifications because researchers correlated higher volatility with higher oil consumption. Correlation does not mean that if you decrease the volatility of the oil you use, your oil consumption will decrease, because there are other oil properties that also affect oil consumption. But it does mean that there is that trend across when a much larger, statistically significant data set is analyzed.

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#4814200 - 07/14/18 07:55 PM Re: Interesting read for all you low NOACK types [Re: JAG]
CR94 Offline


Registered: 03/20/16
Posts: 1179
Loc: Western S.C. since 1996
Originally Posted By: JAG
Intake valves get oil and other substances on them that increase deposits from mostly three sources:
1. PCV flow oil droplets and vapors ...
2. Oil that got past the valve guides
3. Combustion products that got to them from flow reversal out of the combustion chamber.
...
Why not also EGR?
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#4814349 - 07/14/18 11:03 PM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
JAG Offline


Registered: 10/23/05
Posts: 4887
Loc: Fredericksburg, VA
Good catch. I forgot about EGR. EGR crud can be some nasty, sticky, gritty stuff.

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#4814957 - 07/15/18 05:24 PM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
CT8 Offline


Registered: 10/09/14
Posts: 11224
Loc: Idaho
The NOACK is how the oil thickens. The evaporation is insignifiv=cant as compared to everything else drawn through the pvc valve etc.
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#4815228 - 07/16/18 12:53 AM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
JAG Offline


Registered: 10/23/05
Posts: 4887
Loc: Fredericksburg, VA
CT8,
In this paper, it was found that around 80 to 98% of the deposits on the throttle body and intake manifold were from oil that came through the PCV valve. The remainder is fuel-derived.

https://www.tytlabs.com/english/review/rev343epdf/e343_074nakai.pdf

Todayís oils, having more stringent volatility limits than before, thicken mostly due to reactions starting with oxidation, nitration, and sulfation.

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#4816659 - Yesterday at 06:13 PM Re: Interesting read for all you low NOACK types [Re: SubieRubyRoo]
CT8 Offline


Registered: 10/09/14
Posts: 11224
Loc: Idaho
The crankcase is full of oil mist flung from the crankshaft bearings and scraped from the cylinder walls and then whipped up the crankcase windage . This oil has nothing to do with the NOACK.
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