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#3261496 - 01/27/14 12:15 PM Wear comparison for differing OCI - theoretical
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
In the discussion about wear rates for differing oci's, many statements were made about why mathematically you might see certain results.

I thought I would simulate what happens if you do 5000 mile vs 10000 mile oci's and sample at the end of the oci's. Break in wear is assumed to be 200ppm and completed at 5000 miles. Ongoing wear is assumed to be 10ppm per 1000 miles and residual oil in the system is assumed to be 20%.

With these assumptions, the conclusion is that a UOA performed at the end of a 5000 mile oci should show lower wear per 1000 mile than those performed at 10000 mile intervals. The reasoning is simple. More oci's mean more flushing of the break in wear that remains in the system as part of 20% oil leftover after an oil change.

If I recall correctly, dnewtons UOA trending across the same engines showed longer oci's had less wear per thousand miles in longer oci's.


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#3261517 - 01/27/14 12:43 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
Quattro Pete Offline


Registered: 10/30/02
Posts: 25944
Loc: Michigan
Did you see these two real life examples?

http://www.bobistheoilguy.com/forums/ubb...ysi#Post3256034

Granted, top up oil has to be factored in, in such cases...
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#3261528 - 01/27/14 12:51 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
Clevy Offline


Registered: 11/11/10
Posts: 7437
Loc: Saskatoon canada
You're making assumptions. When doing that results may be skewed and unreliable.
Get a few hundred used oil analysis then pick an engine with the most examples and extrapolate from there.
Not that those results will mean much anyways since every person drives differently and their maintenance plans differ too.
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#3261540 - 01/27/14 01:08 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
Ah, I think I have understood Clevys comment as thinking I was saying dnewtons results were incorrect.

No what is meant is that theoretically the result should be shorter oci's exhibit lower wear rates and this is due to more frequent flushing of break in wear (and to a lesser extent regular wear), but the fact that dnewtons statistical analysis shows longer oci's have lower wear rates suggests that longer oci's do in fact provide more protection.

Yes there are more factors to consider.

I actually meant to model the spike theory when UOAs are taken during an oci. Will do that when I have more time but right now my conclusion is that more oci's mean more flushing and less wear to be left behind for spikes so shorter oci's should show a benefit in wear terms regardless of when UOAs are performed.

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#3261602 - 01/27/14 02:04 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
Clevy Offline


Registered: 11/11/10
Posts: 7437
Loc: Saskatoon canada
Originally Posted By: TrevorS
Ah, I think I have understood Clevys comment as thinking I was saying dnewtons results were incorrect.

No what is meant is that theoretically the result should be shorter oci's exhibit lower wear rates and this is due to more frequent flushing of break in wear (and to a lesser extent regular wear), but the fact that dnewtons statistical analysis shows longer oci's have lower wear rates suggests that longer oci's do in fact provide more protection.

Yes there are more factors to consider.

I actually meant to model the spike theory when UOAs are taken during an oci. Will do that when I have more time but right now my conclusion is that more oci's mean more flushing and less wear to be left behind for spikes so shorter oci's should show a benefit in wear terms regardless of when UOAs are performed.


More frequent flushing of contaminants wouldn't do anything in respect to wear because the oil filter traps anything big enough to cause wear,and what the filter misses is too small to do any harm.
So the extra flushing really wouldn't have much effect in relation to wear.
There has to be another reason why longer oil change intervals end up creating less wear over time.
I can't say why with any certainty,only assumptions.
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#3261605 - 01/27/14 02:08 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
Burt Offline


Registered: 01/08/09
Posts: 1044
Loc: texas
Doesn't the validity of your analysis depend on the assumption that the oil filter does not trap wear particles or at least traps them in a manner(over time or relative to particle size) such that it doesn't skew the results?
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#3261656 - 01/27/14 02:58 PM Re: Wear comparison for differing OCI - theoretical [Re: Clevy]
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
Originally Posted By: Clevy
More frequent flushing of contaminants wouldn't do anything in respect to wear because the oil filter traps anything big enough to cause wear,and what the filter misses is too small to do any harm.
So the extra flushing really wouldn't have much effect in relation to wear.
There has to be another reason why longer oil change intervals end up creating less wear over time.
I can't say why with any certainty,only assumptions.


It's not about extra flushing reducing wear, it's to do with more frequent oci's flushing out wear particles more often which should lead to lower ppm per thousand mile readings in UOAs (if wear is linear).

Check out the spreadsheet to understand the logic.

The explanation for lower wear for longer oci's is thought to be the anti wear layer.

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#3261665 - 01/27/14 03:07 PM Re: Wear comparison for differing OCI - theoretical [Re: Burt]
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
Originally Posted By: Burt
Doesn't the validity of your analysis depend on the assumption that the oil filter does not trap wear particles or at least traps them in a manner(over time or relative to particle size) such that it doesn't skew the results?


Yes

But I understand that oil analysis is on particles smaller than a micron.

However, apart from the anti wear layer theory, perhaps more efficient filtering of particles in general as time goes on contributes to less wear seen in actual longer oci's.

And of course, some particles of a size below the filters rating are captured by the filter and more so as it loads up.

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#3261668 - 01/27/14 03:10 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
OVERKILL Offline


Registered: 04/28/08
Posts: 26520
Loc: Ontario, Canada
Originally Posted By: TrevorS

But I understand that oil analysis is on particles smaller than a micron.


No, IIRC, they only pick up particles smaller than 10 microns.
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#3261670 - 01/27/14 03:15 PM Re: Wear comparison for differing OCI - theoretical [Re: TrevorS]
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
The other thing that the spreadsheet shows is that residual oil has no impact on particle count after 20-30 thousand miles ie the high particle count from break in is flushed out by then and we are reaching a steady state with respect to particle counts from residual oil.

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#3261673 - 01/27/14 03:17 PM Re: Wear comparison for differing OCI - theoretical [Re: OVERKILL]
TrevorS Offline


Registered: 07/14/13
Posts: 1281
Loc: California
Originally Posted By: OVERKILL
Originally Posted By: TrevorS

But I understand that oil analysis is on particles smaller than a micron.


No, IIRC, they only pick up particles smaller than 10 microns.


Ok I shouldn't have used a couple of BITOG posts as my source!

In which case, I wonder if dnewton considered if his statistical difference could have been explained by more efficient oil filtering? I have seen him say in several threads that oil filter efficiency ratings don't matter much.

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