Low-viscosity oil and viscosity degradation

[Heliotrope]

A 15% drop in oil viscosity is often bandied about as a threshold that calls for oil replacement.

Where did this figure come from? Is it relevant to today's low-viscosity oils? Low-viscosity ATFs?

 

[friendly_jacek]

Good question. Based on history, good questions generate no answers, silly questions generate endless (silly) discussion.

 

[MolaKule]

Originally Posted By: Heliotrope
A 15% drop in oil viscosity is often bandied about as a threshold that calls for oil replacement.

Where did this figure come from? Is it relevant to today's low-viscosity oils? Low-viscosity ATFs?


Are you referring to condemnation limits?

 

[Heliotrope]

Yes.

 

[MolaKule]

Oil Condemnation Limits as established by Used Oil Analysis cannot be done within a narrow view, it has to be done with a macro or Global view.

http://www.reliabilityweb.com/excerpts/excerpts/getting_the_most.pdf

One oil analysis or snapshot says nothing. This is something we have a hard time getting across to people here on this board and elsewhere.

They get a Used oil analysis, commonly called a UOA, and want people here on the board to analyze what is going on and give them remediation comments. This is not the proper way to do oil analysis.

When doing oil analysis and establishing limits, you have to do what is known as "Trending."

First off, this means taking a sample of the fresh or new
oil currently being used in order to compare it against the UOA when it arrives.

Using the same oil, you then run a specified interval and sample.

You have to do this at least three times with three results, with the same oil, and look for trends or changes, called Deltas.

For example, is the iron level going trending downward after a FF drain? Good.

Stating or applying a single rule of thumb to oil analysis generates a false signal without knowing what would cause say viscosity reduction or viscosity increase.

As an example, let's say we see a trending, not just one analysis snapshot, toward a reduction in viscosity.

In order to make sense of it, we need to look at the root cause or what factors could cause it. Is the oil shearing down because of?

1. Oil formulation (unlikely)

2. Fuel dilution (possible)

3. Racing causing undue stress on an oil too low in viscosity or an oil having a low HTHS?

IN other cases, a condemnation limit for TBN might be set to 1.0 or a percentage drop in tbn over a specified interval. Or for diesel oils, a condemnation limit might be set for a certain soot level, depending on the manufacturers literature.

So the bottom line is, you have to consider a number of factors using trending, driving habits, environmental conditions, etc wrt establishing limits.

What applies to one engine may not apply to another engine.

 

[MolaKule]

For more information on how one company does the actual analysis, see Dave's article

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2498871#Post2498871

 

[Heliotrope]

Thank you for your response. I realize that many factors color the issue, and that a single sample holds little context; however, I do see OEM-issued viscosity condemnation thresholds from time to time.

For example (table on fourth page):

http://www.allisontransmission.com/documents/product/13-TR-90,%20Rev%20E.pdf

Naturally, such a threshold would have to cover a wide variety of hypothetical conditions; however, I am still interested in the manner in which it might be determined. I'm also curious as to whether any OEMs have devised viscosity thresholds for low-viscosity engine oils and ATFs.

 

[MolaKule]

Quote:
I am still interested in the manner in which it might be determined. I'm also curious as to whether any OEMs have devised viscosity thresholds for low-viscosity engine oils and ATFs.


I would say you will have a tough time finding out exactly how they develop those limits as it might be considered IP.

Generally speaking, OEM's develop various limits by bench/lab testing and fleet tests based on very expensive fluid analysis and component tear-down analysis.

 

[Heliotrope]

As a proxy, might one hypothesize that viscosity is sufficient for a given component if an analysis of that component's oil shows that anti-wear additive levels are relatively normal?

 

[MolaKule]

Originally Posted By: Heliotrope
As a proxy, might one hypothesize that viscosity is sufficient for a given component if an analysis of that component's oil shows that anti-wear additive levels are relatively normal?


Well, not additive levels but more accurately wear indicators as per the trending UOA's.

I am currently working on low vis energy efficient 0W30, 0W20 and 0W10 oils using a special Anti-Wear polymer chemistry with a very low level of ZDDP. Testing is showing that the additive levels never change.

 

[Heliotrope]

Thanks, that is very helpful.