TAN and TBN Explanation

[MolaKule]

Originally Posted by SpectroScientific

Background TOTAL ACID NUMBER A high concentration of acidic compounds in a lubricant can lead to corrosion of machine parts and clogged oil filters due to the formation of varnish and sludge. When a lubricant breaks down, acidic by-products will be formed from the chemical decomposition of the base stock and additives in the presence of air and heat. Total Acid Number (TAN) is a measure of acid concentration present in a lubricant. The acid concentration of a lubricant depends on the presence of additive package, acidic contamination, and oxidation by-products. Occasionally, the depletion of an additive package may cause an initial decrease in TAN of fresh oil. However, the accumulation of oxidation by-products and acidic contaminants in an oil over time will always lead to an increase in TAN. This test is most meaningful in industrial machinery applications although sometimes it is recommended in engine applications along with Total Base Number (TBN). TOTAL BASE NUMBER 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, this BN additive is depleted. Once the alkaline additives are depleted beyond a certain limit the lubricant no longer performs its function, and the engine is at risk of corrosion, sludge, and varnish. At this point it is necessary to top-off or change the oil...

See TAN and TBN Instrumentation and more info here: http://cdn2.hubspot.net/hubfs/857680/WP_MeasuringTANandTBN_in_Oil_final.pdf

 

[BHopkins]

Do you know what method of measuring TAN & TBN that the popular motor oil analysis labs use? Interesting read. Thanks for sharing.

 

[UG_Passat]

Don't some esters naturally have some higher TAN from the start, which would be misleading in some analysis on VOA's? I remember Terry Dyson mentioning that on VOA's for Renewable Lube oils.

 

[Brian553]

Originally Posted by BHopkins

Do you know what method of measuring TAN & TBN that the popular motor oil analysis labs use? Interesting read. Thanks for sharing.

https://www.ccjdigital.com/partner-...ng-tbn-in-modern-heavy-duty-engine-oils/ Labs typically test under ASTM D4739

Originally Posted by UG_Passat

Don't some esters naturally have some higher TAN from the start, which would be misleading in some analysis on VOA's? I remember Terry Dyson mentioning that on VOA's for Renewable Lube oils.

Yes, if present, they will increase your TAN

 

[MolaKule]

Originally Posted by UG_Passat

Don't some esters naturally have some higher TAN from the start, which would be misleading in some analysis on VOA's? I remember Terry Dyson mentioning that on VOA's for Renewable Lube oils.

Brian is correct, but it is not misleading, you have to simply adjust your UOA interpretation to accommodate any potential ester component. This is why I keep telling people that without a current VOA of the oil you have put into the engine, any subsequent UOA interpretation is pretty much useless.

 

[UG_Passat]

People tend to use Blackstone and they nickel and dime you for TBN and TAN tests. I've had blackstone question a Renewable Lubes VOA as being a UOA instead, due to the initial TAN of the esters.

 

[MolaKule]

Amanda from Blackstone states that the TAN testing is based on ASTM D664 and the TBN testing is based on ASTM D4739.

 

[NuttCase]

whereas diesel engine oils tend to be higher (15-30 mg KOH/g) due to the more severe operating conditions. This must refer to heavy duty diesel engines only. Most modern European passenger car diesels require ACEA C2/3/5 and the TBNs are no different from petrol engines - typically between 6 and 8 - never seen a Cx oil with more than 10. Question for the experts - do the dispersents, detergents etc contribute to the TBN ?

 

[CarfriendXX]

Maybe someone could explain again why a high TBN is not good for today's direct injection turbo engines. Mobil 1 says that the fs 0W40 with a TBN of 13 is intended for heavy use with direct injection turbo. My thought so far has been that TBN was lowered and midsaps was introduced due to exhaust aftertreatment. Am I so wrong?

 

[BMWTurboDzl]

Maybe someone could explain again why a high TBN is not good for today's direct injection turbo engines. Mobil 1 says that the fs 0W40 with a TBN of 13 is intended for heavy use with direct injection turbo. My thought so far has been that TBN was lowered and midsaps was introduced due to exhaust aftertreatment. Am I so wrong?

It's because the higher starting TBN is usually met by using additives which when burned travel through the PCV system and end up as deposits on the back side of the intake valves. The amount of deposits depend on the design of the PCV system and engine tuning.

Per Lubrizol circa 2006 the additive chemistry behind ACEA Cx oils results in comparatively less intake deposits all else being equal. The introduction of ULSD/ULSG allows for the use of these ACEA Cx additives which is why these oils have been used in W. Europe for over 15 years.

As I understand it higher Sulphur levels are a major contributor to the development of acids which necessitated the need for oils with high TBN via heavy doses of ZDDP. HDEO oils were always highly additized because they were used in trucks burning fuel which contained 500 ppm of sulphur. The downside is that when burned these oils left behind a lot of ash and the amount was incompatible with and would cause the premature failure of DPF as well as TWC (gas) and GPF*


Max sulphur levels for US diesel were 5,000 ppm < 1993. 500 ppm 1993-2006, 10 ppm 2006+ ULSG is ~10 ppm as of 2020 or thereabouts

*New requirement for EU countries.

 

[CarfriendXX]

Thank you for the explanations. Accordingly, you can use midsaps, especially at shorter intervals, and take advantage of the lower deposits. If zinc and phosphorus are lower than with fullsaps, is this also positive for the cleanliness of the valves?

 

[BMWTurboDzl]

Thank you for the explanations. Accordingly, you can use midsaps, especially at shorter intervals, and take advantage of the lower deposits. If zinc and phosphorus are lower than with fullsaps, is this also positive for the cleanliness of the valves?

The intake valves on a DI-only engine will never be as clean as the intake on a PFI engine. However using a ACEA Cx oil should result in less buildup vs ACEA A3/B4. The amount of build up in both cases is going to depend on the engine and how much oil it's burning.


Real world example:

Circa 2007 BMW N54 was I6 TGDI and intake buildup would cause drivability issues at around 50k miles. The recommendation was walnut blast every 45k miles or so. Circa 2010 BMW N55 was also I6 TGDI and a replacement for the N54. BMW recommends a walnut blast every 100k miles for the N55. Both engines are spec'd for ACEA Ax/Bx oils but the N55 has a revised PCV system. Photos by owners of high mileage N55 US based engines show some buildup but nothing crazy.

 

[CarfriendXX]

So if my vehicle does not tend to consume oil, wouldn't it be so tragic if you take an a3 oil instead of a c3? Then you would have the "better" wear protection without the disadvantage of excessive valve deposits? Are there still amateurs outside the valves possible deposits with an increased TBN?