LUBE TIPS- TBN #'s

Status
Not open for further replies.
Joined
May 27, 2002
Messages
1,873
Location
Ocala, Florida
How do tbn numbers and sulfated ash levels relate to engine oil performance?

Sulfated ash and TBN are two of the physical and chemical measurements made on the engine-oil. They are not a direct measure of an engine oil's performance. The higher the number is not necessarily better.

Sulfated ash is a direct measure of the amount of oil additives that contain metal. These metallic base additives make up the detergent and anti-wear additive systems that prevent deposits and wear. They generally contain metals such as calcium, magnesium and zinc.

The total base number (TBN) is a measure of the engines oil's ability to neutralize any acids that may be formed during the combustion of the diesel fuel. Historically, the higher the engine oil's total base number the better its ability to neutralize any acids that may be formed. However, starting out with a high TBN DOES NOT GUARANTEE that the engine oil will RETAIN its high level of TBN during service. With the drive by users and equipment manufactures toward extended engine oil drain intervals and the future of exhaust gas recirculation to reduce emissions there is a greater need for the engine oil to contain an effective detergent/dispersant additive system that will not only effectively neutralize any acidic components that may be formed, but also retain its TBN throughout the engine oil's drain interval.

An engine oil's tbn will reduce over time and use. Today's diesel engines are designed to have lower oil consumption rates and smaller sump capacities. With the desire for longer oil drain intervals and engine oil that has a tbn of 8, 10 or even higher could actually have a tbn of 4 or 5 by the time the oil is either refreshed though makeup or changed. Therefore, it is critical that an engine oil exhibit very good to excellent tbn capability in order to prevent engine wear and bearing corrosion.

The ability of an engine oil to retain its tbn throughout the engine oil's drain interval is dependent upon the type of detergent/dispersant additive chemistry used in it formulation.

An all calcium based detergent/dispersant additive package that not only effectively neutralizes any acidic components that may be formed but also can provide excellent tbn retention over the engine oil's drain interval.

Most heavy duty diesel engine oils contain either a high magnesium based or a calcium/magnesium based detergent dispersant additive system. Magnesium base detergent systems though they will neutralize acids as the are formed, do not have the same effective acid neutralizing capabilities as an all calcium based additive system. Magnesium based detergent additive systems do not neutralize any of the weak acids that may have been formed by the combustion of the diesel fuel. These weak acids over time can build up in the engine oil eventually causing the engine oil to rapidly lose its tbn retention.

Magnesium based detergents are primarily used in the formulation of car engine oil formulation because of their ability to allow these engine oils to pass the various engine sequence tests used to measure wear protection. However, in heavy duty diesel engine oils magnesium base detergents can cause higher wear in the ring-belt area of a diesel engine. Magnesium based detergents from magnesium oxides when the neutralize acids, a by product of the acid neutralization reaction. Magnesium oxide is very hard in consistency and can abrade and polish cylinder walls.

Calcium based detergents on the other hand form calcium sulfate when they neutralize acids. Calcium sulfate is very soft and fluffy in consistency and is soluble in oil. Calcium based detergents in addition have been found to enhance a diesel engine oil's ability to provide excellent high temperature piston cleanliness, provide excellent protection against bore polishing and enhance the soot handling capabilities of the engine oil.

How high of a TBN is really necessary and how critical is the number?

This question comes up continually, and it deserves some clarification. TBN is not a measure of an engine oil's performance, and an engine oil with a higher TBN number such as 13 or 14 is not necessarily better than an engine oil that has a tbn of 10. There are two things that are more critical to know about TBN than its starting point: how it measured and the rate at which it depletes.

The ASTM has tree methods for measuring TBN. If these three different test methods were used to test the same new oil, each method would give three different answers. In other words, the TBN rating of an engine oil is affected by the test method used to measure it. It is Schaeffer Mfg's experience and the experience of many other oil analysis lab's that the ASTM d-2896 test method will produce a higher TBN rating and the D-4739 test method will result in a lower number. The third method ASTM D-664 is now an obsolete test method and is only used to measure the total acid number of lubricating fluids such as hydraulic fluids. Most companies use the ASTM D-2896 test method to measure the TBN of a new oil.

However, when testing used engine oil, it is the ASTM D-4739 test method that provides the most reliable results. The ASTM-D4739 test method more accurately reflects the level of neutralizing power left in the engine oil after use. The ASTM D-2896 test method, because ir measures the high end of alkalinity, may indicate that more base is left in the engine oil than what may truly be left in the engine oil or is advisable for continuing service.

Most used oil analysis programs use the ASTM-D2896 method unless another test method is requested, because This test method is easier and faster to run. Since TBN is a very critical factor especially with the advent of EGR containing engines, which will produce and introduce more acidic components into the engine oil and you're trying to extend oil drain intervals, the ASTM D-4739 test method should be used and specified by you.. The ASTM D-4739 test method provides a more accurate indication of serviceability, especially if trying to extend oil drain intervals.

The second important feature of TBN, more critical than how high high it is rated, is the rate at which it depletes during use. As we stated in the previous question on tbn some engine oil start with a high tbn and then drop and lose their neutralizing ability quickly. Other engine oils can start with a lower tbn, deplete at a slower rate and maintain their alkalinity for a much longer period of time. Naturally, what is important is how well an engine oil can maintain its tbn during service. The real value of a tbn number is not determining an engine oils quality; it is in making sure an engine oil is not becoming corrosive at the engine of a drain period.

This is another case of requirements changing with the times, and the old tradition of a tbn level of greater than 10 for otr vehicles cannot be used as a rule of thumb anymore. Engine designs have drastically changed over the years and fuel sulfur levels have dropped significantly during the last decade, so that even in off road application where fuel sulfur can be as high as 0.5%, the demand for a very high tbn rating cannot really be justified. What is more important is how the engine oil's tbn will last and maintain it neutralizing ability over the entire oil drain interval.
 
Great Info Bob:

Bob,

I posted a similar response to an additive question in the main Car and Truck Lubrication theread. I have added some info.

An additive is a chemical, which when added to an oil, imparts or enhances desirable functional properties to the base oil.

Deposits and wear limit the life of any machine. Detergents and Dispersants (sometimes the same chemical is used for bioth) keep sludge, carbon, and other deposit precursors (derived from partial oxidation of the fuel or lubricating oil) suspended in the oil.

Calcium and magnesium "sulfonates" are ash-type (metallic) detergent compounds in fully formulated oils and provide the detergency required to remove carbonaceous and other materials from surfaces.

If the calcium and magnesium is in the form of "phenates" (calcium and magnesium phenates) then the additive is a multifunctional additive which:

1. provides detergency
2. is used to attack acids and keep the TBN at a descent level (sometimes calcium carbonate is added to increase the BASE characteristic).
3. acts as an oxidation inhibitor.

More specifically, calcium alkyl phenates are used for piston deposit control, reduce or eliminate ring sticking, and control oxidation products.

The overbased calcium sulfonates provide low cost and good performance.

One has to be careful not to overdo the "overbased" sulfonates, since this creates a "pro-oxidation" conflict with anti-oxidants such as ZDDP. Addition of overbased "phenates"
does not create a conflict with other anti-oxidants such as ZDDP or other organometallic esters.

Many modern Detergent/Dispersants are ashless and are succinimides, succinate Esters, and polymeric viscosity improvers (VII's). Yes VII's can also do double duty as detergents/dispersants.

Dispersants surround the sludge particles with "micelles" or little pockets of chemicals that hold sludge and other contaminats in the oil itself. Without dispersants, the contaminants would coat moving parts inside the engine and formclumps of lacquers, sludge deposits, and wear materials.

Antioxidants reduce the oxidation of the oil and increase thermal stability. They do this by attacking various "peroxides" in the oil formed by combustion processes, most notably, "blow-by." ZDDP's, dispersant/detergent, and some VII's also act as anti-oxidants.

Friction reduction or friction Modification (FM) compounds and anti-wear compunds reduce friction among moving surfaces by depositing a very thin layer of a film that acts as a semi-solid lubricant. Usually, an "organometallic film" is deposited on the iron (Fe) in a "three-layer" system. The base metal is overcoated with Ferrous oxates, and upon that the organometallic film is deposited. Most organometallic films are composed of zinc phosphates, Moly compounds such as Moly Sulphides, or Antimony Sulphides. Zinc dialkyl- or diaryldithiophosphates (ZDDP), Molybdenum dithiophosphates (from Moly dithio- or dialkydithiocarbamates), and Antimony dithiocarbamates are some of the better additives. These additive created films all act as a boundary lubricant when hydrodynamic lubrication fails, preventing metal-to-metal contact . These additives work essentially the same way, the only difference among them being the temperature of activation and the temperature at which oxidation, pressure and "shear" will remove these films. Some ester fluids and VII's also acts as FM's.

Extreme Pressure or EP additives are usually organometallic compounds of chlorine, sulphur, phosphorous, and other metals which coat metal surfaces with a soft metallic surface layer that "shears" easily. The theory here is that it is better to shear a soft metal layer than the base metal itself. EP compounds are usually used in differentials, transmissions, and gear boxes, where extreme contact pressures exist.
 
Bob/MolaKule
So is 1.3% Sulphated Ash in Delvac 1 bad in my Mazda/Subaru petrol engines? TBN is 11. If bad what is the max % Sulphated Ash I should look for in a syn or syn blend oil? Wish schaeffers had a S7000 10W40 or 5W40 even? tks..s
 
sprintman,
I personally think that the Delvac I is the best oil that Mobil has to offer in their synthetic line. If I were using Mobil in anything, it would be the Delvac I. The question of the high Phos. and the sulfated ash levels comes up every time on using this oil in a petro auto. I would not worry about either one. I have read articles some time ago, using a bore scope to check the cylinder walls and the effect was nil from the sulfated ash.
Delvac I is a top of the line oil available to you and I would use it and smile. IMHO
 
Sprintman,
I am looking at a spec sheet that shows the Castrol Syntec 5/50 as having 1.2 percent just to give something to compare with. Of course it is not a energy conserving class oil but it is a gasoline engine oil.

[ August 15, 2002, 09:35 AM: Message edited by: dragboat ]
 
dragboat
Thanks I think I'll use D1 after another Auto-Rx clean on my Mazda Turbo. will trial Redline 5/10W40 in the Sube for summer. What class boat are you involved with? I like the twin screw TFH boats.
 
"So is 1.3% Sulphated Ash in Delvac 1 bad in my Mazda/Subaru petrol engines? TBN is 11."
No, with some qualifications.
1. As long as engine temps are kept normal. Low engine temps favor intake valve deposits.
2. Add combustion cleaner or fuel system cleaner at each oil change to keep ANY deposits at bay, not just ash deposits.

"If bad what is the max % Sulphated Ash I should look for in a syn or syn blend oil? Wish schaeffers had a S7000 10W40 or 5W40 even? tks..s "

Any ash content below 1.5% seems to work.
I will be using Schaeffer's 15W40 here shortly in farm machinery and my son's Mercedes.
The specs appear darn good. You may want to try it as well.

D1 is a very good mix-fleet oil.
 
Also keep in mind that a high ash content isn't as harmful as you think as long as the Noack value is lower. With less oil evaporating, there will be less ash deposited on the parts. So you're better off running an oil with 1.5% ash content and 5% on the Noack value, than you would be running an oil with 1.0% ash content but 15% on the Noack.
 
Excellent point, here here!
cheers.gif
 
Bringing this one up to the top. Great information..

A question on the article.. at what level is TBN considered depleted? I
Is anything above 0 still performing the function or is the ability to neutralize acids proportional to the number?
IF a oil quickly depletes to a low number but holds steady is that as good or better since the TBN did some work than an oil that maintains a very high TBN throughout the interval.
In other words.. what good is a TBN number that doesn't go down with use other than being a high #? Is it just noty working effectively?
 
My rule of thumb is when TBN drops to 50% of new oil you are still OK at 75% of new oil you are getting to the end and should start a time frame for a drain. example a 10 TBN oil will be getting close at about 2.5 since motor oils generally
form acid and oxidize at a non linear rate they go to heck faster the longer they are in use.
bruce
 
Hi,
Detroit Diesel have the following TBN condemnation limits for all 2 & 4 cycle HD engines;

D4739 = 1 or,
D2896 = 2

As well they say a TBN 70% less than new oil should be the limit with high sulphur fuel

For the past two decades I have always used the DD limits as the absolute minimum along with the TAN report as part of my UOAs
However, maximum soot levels have always been reached prior to reaching the TBN minimum

The lowest TBN we have experienced is 1.37 (D4739)

The highest TAN reached has been 7

Regards
Doug
 
Hi,
Bryanccfshr - a quick check of my UOA database regarding initial TBN reduction and "leveling off" revealed this;

a)there is a relatively high initial depletion

b)the "leveling off" is maintained over a long period

c)the "leveling off" in my case is probably due to minor initial oil consumption (first 30kkms after OC) followed by a constant top up rate (average 1ltr/6k over whole OCI) over around 100kkms

I am a great believer in a regular and documented top up routine during extended OCIs

The increasing TAN confirms the above

Regards
Doug
 
Thanks Doug Hillary,

This seems intuitive, particularly after the Famous 3MP study. I lack the technical language and training required to word this properly therefore I will use laymens terms. Forgive my oversimplification.
The way I see it starting TBN matters less than its rate of depletion. although the number is getting lower it is still doing the "work" of neutralizing harmfull acids but as it is a battle of attrition. At a certain point the base numbers are going to suddenly go from a stable level toto rapid depletionn when there is no longer enough active additive to fight the assualt from contaminants.
I am interested in learning the terms defining this point in oil life that it is no longer usefull and how different formulations compare in resisting that final drop to the point that the additives are no longer doing the job.
I don't think the virgin number tells the whole story when we read a VOA on how well the TBN will be maintained as it is hard to tell the difference between rapidly depleting additives and those that are time and heat activated, functioning differntly yet all contributing to the total number.
What if the TBN in a UOA stays high yet the TAN is revealed to be high as well, is the TBN not working, Simply failing to react? That is my driving point.
 
Hi,
Bryan, like you I think the virgin TBN only needs to be high enough to equal the needs of the engine "family", considering the quality of fuel used, the application and the OCI anticipated
I believe that the combustion processes involved have the greatest effect in a heavily utilised and loaded engine even with low sulphur fuels

I have never seen a rapid depletion in TBN numbers unless associated with an engine fault
As well, I have used the TAN to confirm or deny the reported TBN and whilst not in synchronisation they, along with reading the other oil degredation factors, provide a meaningful picture. Many times I have asked for another UOA when all the other factors do NOT point to a low TBN or higher than expected TAN

Some engine makers do NOT provide a TAN limit. Some engine oils seem much better than others at handling progressive degradation. With diesels, I have no doubt at all that some oil formualtions will hand soot levels as high as 6% with ease

Regards
Doug
 
Here is an interesting question I have been researching for some time:

At what level of TAN or TBN in a lubricant does one actually see corrosive action on metals in order to see say a 25 ppm loss or 100 mcgram loss in either ferrous or copper alloy materials.

In other words, what is the equivalent pH level that crosses the threshold to produce corrosive action in which the metal is removed and put into solution?

I have yet to see a definitive paper that shows a good correlation.
 
Status
Not open for further replies.
Back
Top