Relationship between TBN & Varnish, SAE Publication #981444

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I was reading the SAE article presenting the Mobil1 "Aunt Minnie Test", and came across this statement that I'd like folks here to explain to me (page 766 of the original publication): "...the lower detergency of Syn E (7.2 TBN) vs. Syn F (11.8 TBN) appeared to have some effect on piston cleanliness in side by side testing in the 2.0 L 4 cylinder engine. The vehicle running on Syn E gave an average piston varnish of 6.2 compared to 8.1 for SynF." Syn E and Syn F are two different synthetic oils used in this test.

(1) The authors of this study are talking as if it is reasonable to expect a higher TBN to allow an oil to clean up more varnish on the pistons, correct?

(2) The piston scores are higher is better, correct?

I have always thought of TBN as simply reducing acid, and in turn, the likelihood of acid corrosion.

(3) But these authors are suggesting that it also will fight deposits, or have I read too much into their statement?
 
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MolaKule

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I was reading the SAE article presenting the Mobil1 "Aunt Minnie Test", and came across this statement that I'd like folks here to explain to me (page 766 of the original publication): "...the lower detergency of Syn E (7.2 TBN) vs. Syn F (11.8 TBN) appeared to have some effect on piston cleanliness in side by side testing in the 2.0 L 4 cylinder engine. The vehicle running on Syn E gave an average piston varnish of 6.2 compared to 8.1 for SynF." Syn E and Syn F are two different synthetic oils used in this test.

(1) The authors of this study are talking as if it is reasonable to expect a higher TBN to allow an oil to clean up more varnish on the pistons, correct?

(2) The piston scores are higher is better, correct?

I have always thought of TBN as simply reducing acid, and in turn, the likelihood of acid corrosion.
Since I don't have access to the paper's text or graphics I can only comment on the author's text.

The tests referred to is most likely one of the ASTM D7843 membrane patch colorimetry (MPC) type tests or older similar tests.

Varnish is: "a thin, hard, oil-insoluble deposit, composed primarily of organic residue and most readily definable by color intensity. It is not easily removed by wiping with a clean, dry, soft, lint-free wiping material and is resistant to saturated solvents. Its color may vary, but it usually appears in gray, brown, or amber hues.” So color hue and intensity of the resulting varnish is given a rating, but if the paper didn't state a standard for varnish deposit grading, then who knows what they used to judge and grade it.

There are many different chemistries and internal engine conditions that can affect varnish buildup or cleanliness.

An oil's volitivity can form vapors that condense on relatively cooler engine parts to form varnish and other carbonaceous deposits.

I would not assume an oil with a higher TBN can directly correlate to engine cleanliness as there are many factors such as base oils used, DI additive package chemistry, and operational envelopes (programming) that can affect it.
 

paulri

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On p. 762, they give "Sequence VE," and quote numbers that look a lot like the minimums for the API certifications (SJ, SP, etc.), so I believe they were simply using the one that would be commonly used (SG rating required 6.5 rating, which is cited on that same page). The top of p. 762 has "API Gasoline Engine Test Results for Syn A, Syn B, and Syn D."

Varnish is: "a thin, hard, oil-insoluble deposit, composed primarily of organic residue and most readily definable by color intensity. It is not easily removed by wiping with a clean, dry, soft, lint-free wiping material and is resistant to saturated solvents. Its color may vary, but it usually appears in gray, brown, or amber hues.” So color hue and intensity of the resulting varnish is given a rating, but if the paper didn't state a standard for varnish deposit grading, then who knows what they used to judge and grade it.
 

paulri

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Time for me to flog that dead horse here. OK, assuming that everything you wrote below is true--could someone make the argument that two oils, with all other things being equal or the same--all those factors that you mentioned below--that if one oil had higher TBN, then one could expect less varnish? I'm not trying to ask if higher TBN will always, with every oil formulation, give less deposits & varnish than any lower TBN oil. All I'm trying to figure out is if a higher TBN will assist in lowering the varnish deposits. And if so, then how....

I would not assume an oil with a higher TBN can directly correlate to engine cleanliness as there are many factors such as base oils used, DI additive package chemistry, and operational envelopes (programming) that can affect it.
 
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MolaKule

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Time for me to flog that dead horse here. OK, assuming that everything you wrote below is true--could someone make the argument that two oils, with all other things being equal or the same--all those factors that you mentioned below--that if one oil had higher TBN, then one could expect less varnish? I'm not trying to ask if higher TBN will always, with every oil formulation, give less deposits & varnish than any lower TBN oil. All I'm trying to figure out is if a higher TBN will assist in lowering the varnish deposits. And if so, then how....
Some Background info on TBN: Total Base Number (TBN) is a measure of alkaline concentration present in a lubricant. Engine oils are formulated with alkaline additives in order to combat the build-up of acids in a lubricant as it breaks down. The TBN level in a lubricant is targeted for its application. Gasoline engine oils are typically formulated with starting TBN around 5-10 mg KOH/g whereas diesel engine oils tend to be higher (15-30 mg KOH/g) due to the more severe operating conditions. Specialized applications, such as marine engines, may require >30 mg KOH/g.

As the oil remains in service, all additive chemistry tends to decompose via oxidation and blowby contamination, so its effectiveness degrades over time. The longer the oil remains in service, the potential risk of corrosion, sludge, and varnish increases. This is why the need to change the oil.

Picking out one oil property or one DI chemistry component as a single cause of this or that is an exercise in futility.
 
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""I would not assume an oil with a higher TBN can directly correlate to engine cleanliness as there are many factors such as base oils used, DI additive package chemistry, and operational envelopes (programming) that can affect it.""

Yes I think this is correct and would be very syn/formulation dependant
 
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Since I don't have access to the paper's text or graphics I can only comment on the author's text.

The tests referred to is most likely one of the ASTM D7843 membrane patch colorimetry (MPC) type tests or older similar tests.

Varnish is: "a thin, hard, oil-insoluble deposit, composed primarily of organic residue and most readily definable by color intensity. It is not easily removed by wiping with a clean, dry, soft, lint-free wiping material and is resistant to saturated solvents. Its color may vary, but it usually appears in gray, brown, or amber hues.” So color hue and intensity of the resulting varnish is given a rating, but if the paper didn't state a standard for varnish deposit grading, then who knows what they used to judge and grade it.

There are many different chemistries and internal engine conditions that can affect varnish buildup or cleanliness.

An oil's volitivity can form vapors that condense on relatively cooler engine parts to form varnish and other carbonaceous deposits.

I would not assume an oil with a higher TBN can directly correlate to engine cleanliness as there are many factors such as base oils used, DI additive package chemistry, and operational envelopes (programming) that can affect it.
I doubt they a judging by methods like the patch test. They are most likely using the standardized parts rating procedures which, for deposits, was CRC Manual 20. It was superseded by ASTM Manual 20 sometime around 2009. The method looks at varnish, sludge, rust and carbon in 2- and 4-cycle, combustion chamber, piston deposits and other component deposits. It provides a ratings environment and the necessary scales. This is how major oil and additive companies develop engine oils and chemistries.
 

MolaKule

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I doubt they a judging by methods like the patch test. They are most likely using the standardized parts rating procedures which, for deposits, was CRC Manual 20. It was superseded by ASTM Manual 20 sometime around 2009. The method looks at varnish, sludge, rust and carbon in 2- and 4-cycle, combustion chamber, piston deposits and other component deposits. It provides a ratings environment and the necessary scales. This is how major oil and additive companies develop engine oils and chemistries.
Here is what I stated:

"The tests referred to is most likely one of the ASTM D7843 membrane patch colorimetry (MPC) type tests or older similar tests."
 
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Here is what I stated:

"The tests referred to is most likely one of the ASTM D7843 membrane patch colorimetry (MPC) type tests or older similar tests."
The Manual 20 method is not a test, it's the rating system used by people across the oil, additive and auto industries. It was used in 1998 when this paper was written and it is still used today under ASTM. Your definition of varnish is accurate but is is a visual evaluation against standards and not a test as in an ISO or ASTM test. Manual 20 looks are deposits and Manual 21 looks at distress of engine and drive train parts. Manual 21 used standard distressed part for comparison
 
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In all my years playing around with the slippery stuff, I was always somewhat dismissive of piston varnish as a 'thing'. I tended to equate colleagues who banged on about it to women that worry about Visible Pantie Line.
 
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In all my years playing around with the slippery stuff, I was always somewhat dismissive of piston varnish as a 'thing'. I tended to equate colleagues who banged on about it to women that worry about Visible Pantie Line.
You're right. A little varnish here and there is not a big deal. But it is important in engine oil development projects such as advancing from one category to the next or in developing an oil that needs to be changed only three or four times in the life of the car. the rating system is also used for diesels and 2-stroke engines as well.
 
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You're right. A little varnish here and there is not a big deal. But it is important in engine oil development projects such as advancing from one category to the next or in developing an oil that needs to be changed only three or four times in the life of the car. the rating system is also used for diesels and 2-stroke engines as well.
Have you ever seen an engine test fail on varnish? I can't recall that I have. Sequence IIIG pistons fail because they are black, carbon encrusted monstrosities, not because the metal is a marginally different shade of silver.
 
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