What should the minimum TBN be for a UOA?

[skyship]

There seem to be three schools of thought on what the minimum TBN for a UOA should be before the oil is changed as follows:
1/ Backstones > 1
2/ Various experts > 3
3/ Some oily document > Half of the VOA TBN.
I use no 2 and would not use my Synthoil below a TBN of 3, but I would be interested in what other folks use as a minimum figure and why.
I like Blackstones, but they do seem to be rather keen on extending OCI's and once an oil shears it is the additives that save the day.

 

[barlowc]

I think it may vary from one oil to the other.

In my last UOA for our Saturn, where I ran SynPower for nearly 7900 miles, the TBN was 1.8. Blackstone noted, "You'll note the TBN dropped from 5.5 last time to just 1.8 here. That's mainly due to the differences in the calcium level of the oil going in." (The previous TBN of 5.5 that they reference was a 6300 mile run of Platinum.)

 

[Artem]

I personally use Blackstone's recommendation but add 1.0 TBN as a safety buffer. Oil is cheap, engines are not.

So I stop at 2.0 TBN on Blackstone's scale.

 

[skyship]

This is a link to the document that says about the half or VOA figure:
http://www.bunkering.co.kr/bp/terminology/TBN.htm
My LM Synthoil 5/40 was 9.6 in the VOA and 4.7 at the 10K km OCI, although my 1.9 TD is a lot smaller than the big diesels that document is for.

 

[fdcg27]

I agree with you.
Still, as long as no unusual amount of wear or oxidative thickening is found in a UOA, whatever TBN ends up at is probably okay.
I do like to leave some oil life on the table, though, simply because it may not be convenient to do a planned change until another 1K or so has elapsed.
If the oil still has a decent TBN level at your planned change interval, then you know you'll do no harm in running a bit past it.

 

[skyship]

I just found this document about TBN & TAN depletion rates:
http://www.oil-lab.com/downloads/TBN-1.pdf
It does say that different engine manufacturers have different minimum recommended TBN figures and they were only looking at big truck engines. Some say one half and some one third of the original number.
It could be that smaller diesels are less sensitive than bigger ones, BUT I still have not read anything to justify Blackstones 1 figure as a minimum.

 

[edhackett]

It depends on the ASTM method used to determine the TBN. If you don't know that, you can't set a condemnation point, as the two give different results.

From Chevron:
Quote:
How is TBN measured? It is important to note there are several test methods for Total Base Number. The one used in product data sheets is generally ASTM D 2896. This method uses perchloric acid to neutralize the alkalinity in the oil and yields a slightly higher number than the test method used by the oil analysis labs. They generally use ASTM D 4739 and the acid used here is hydrochloric acid. This produces a number approximately 2 mg KOH/g LOWER than ASTM D 2896 for the same oil. Due to chemical interferences, this test method does not recognize all of the alkalinity that ASTM D 2796 sees.

Why are there two test methods? The oil manufacturers have typically used ASTM D 2896 and their labs are set up to handle perchloric acid, which is toxic and hard to handle. In addition ASTM D 2896 can measure both the “hard base” from metallic detergent as well as the “soft base” from organic, non- metallic ingredients. So it is a more accurate method. BUT, the production oil analysis labs prefer to use a safer and easier to use titration acid, namely hydrochloric acid. The tests can be run faster, more cost effectively and more safely.


Blackstone uses 4739, we have seen UOA's from labs using 2896. If in doubt, ask the lab.

I would use 2.0 for 4739 data and 3.0 for 2896 as safe, conservative condemnation points.

Ed

 

[skyship]

I figure that the one third of VOA seems a reasonable minimum and will stick to 3, but I am still curious as to how Blackstones set the minumum at 1 and as I have not found any documents or articles saying that figure is OK, I will e mail them to see what they say.

 

[skyship]

Just got this back from Blackstones about why they chose 1 as the minimum TBN:
Thanks for the e-mail.
I came up with the value of 1 because it seemed like a good stopping point and is easy to remember. For a lot of the oils we see, we don't know where the starting TBN is, so we can't use a ratio like 1/3 of the starting point, but you can use that as a stopping point on your samples if you like.
Let me know if you have any more questions.
Sincerely,
Ryan Stark
Blackstone Labs

 

[edhackett]

That's likely a good point to change. This is also from Chevron, ASTM D 2896 method, assuming diesel. There was no explanation of the Severity levels.

Quote:
How much TBN do we need to protect the engine? The old rule was to change the engine oil when 50% of the new oil TBN had been consumed. Because of the virtual absence of fuel sulfur today, much less is needed. Chevron now sets the TBN guidelines for all of its diesel engine oils as follows:
FOR ALL OILS when using ULSD
• Severity 1: 50%-44% of new oil TBN or 3.5 to 4
• Severity 2: 43%-36% of new oil TBN 3 48 to 2.9
• Severity 3: • Severity 4: less than 2 div>


I wish Blackstone had been a bit more helpful than their "we pulled the number out of our behinds" reply. I don't know if their 1.0 corresponds to Chevron's Severity 3 or 4. You might send them this and ask for a clarification if one should add 1.0 or 2.0 to their numbers to correspond closer to ASTM D 2896.

Ed

 

[Quattro Pete]

Has anyone ever seen a report with a TBN of less than 1, even after a very long OCI?

From what I've read, it's practically impossible for this to happen, hence having a condemning value of 1 is rather useless.

 

[INDYMAC]

I have seen a couple go below 1.0. But I seem to remember coolant and/or fuel contamination being high.

But why the focus on TBN? Shouldn't people be more concerned about TAN rising rapidly? That would be a bigger concern for me, rather than what is the TBN number. The TBN is useless if it no longer controls acids.

 

[edhackett]

There's a UOA posted now, a Corolla with 11.3K on Amsoil that came back with a TBN of 0.2. I've seen a UOA here with a 0 TBN.

Ed

 

[Quattro Pete]

And yet it did not appear to hurt anything, which begs the question: why even worry about TBN?

 

[edhackett]

Because the TBN is essential in controlling deposit formation(sludge). You don't see that in a UOA.

Ed

 

[Quattro Pete]

Wouldn't it show up as elevated insolubles?

 

[skyship]

The Chevron table is interesting, BUT it is a pity there is no definition of the severity of service levels listed.
As regards some of the other posts, the TAN might be of use in figuring out when an oil is running out of active additives, BUT they charge extra for that number, so not many folks obtain it.
The TBN figure is important as is does give an idea of when the risk of sludge formation starts and when the action of the anti wear additives that provide a secondary level of protection once the oil film shears have declined.

Originally Posted By: edhackett
That's likely a good point to change. This is also from Chevron, ASTM D 2896 method, assuming diesel. There was no explanation of the Severity levels.

Quote:
How much TBN do we need to protect the engine? The old rule was to change the engine oil when 50% of the new oil TBN had been consumed. Because of the virtual absence of fuel sulfur today, much less is needed. Chevron now sets the TBN guidelines for all of its diesel engine oils as follows:
FOR ALL OILS when using ULSD
• Severity 1: 50%-44% of new oil TBN or 3.5 to 4
• Severity 2: 43%-36% of new oil TBN 3 48 to 2.9
• Severity 3: • Severity 4: less than 2 div>


I wish Blackstone had been a bit more helpful than their "we pulled the number out of our behinds" reply. I don't know if their 1.0 corresponds to Chevron's Severity 3 or 4. You might send them this and ask for a clarification if one should add 1.0 or 2.0 to their numbers to correspond closer to ASTM D 2896.

Ed

 

[cp3]

I just got a reply from Toromont, they use Dexil TBN Method D5984-96. Anyone know how this compares to the other two methods mentioned?

 

[edhackett]

It doesn't really correspond to any of the ASTM methods, but since it uses hydrochloric acid as a reagent(not the titrant), it would be closest to ASTM D 4739.

They list the MDL at 0.6 TBN, accuracy of +/- 10%+MDL, and MQL at 1.8 TBN.

This means that if you receive a TBN reading of 4.0, that's 4.0 +/-1.0 and the method cannot accurately measure TBN below 1.8.

Ed

 

[edhackett]

As far as the severity levels... In looking at them, I would give them the following color codes based on their recommendation of changing at 33% of the initial TBN:

Severity 1 = Yellow
Severity 2 = Orange
Severity 3 = Red
Severity 4 = Flashing red plus a loud alarm

Ed