TBN | Blackstone Laboratories

TBNs & TANs: Part 2

In our last newsletter, we did a deep dive on the science behind the Total Base Number (TBN) and Total Acid Number (TAN), and what information we can (and can’t) glean from these tests. Go back and check that one out if you missed it. For this article, we went into the lab for a more hands-on approach, and encountered a few surprises along the way. Let’s roll up our sleeves and start experimenting!

How Does Heat Affect the TBN?
We know a variety of factors impact the acidity of engine oils, but we wanted to isolate just one variable to measure its impact. Heat was the obvious choice, for two reasons. First, overheating is a common problem, and we often find increases in wear, viscosity, and insolubles after even brief overheats, so clearly heat causes the oil to change. Second, heat is pretty easy to replicate in a laboratory setting. So we broke out the hot plate and got to work!

We took three samples of Rotella T 15W/40 and tested oil at three different temperatures:
-212°F (normal operating temp)
-302°F (upper end of most oil temp gauges)
-392°F (a temperature your oil hopefully never sees, at least not for long!)

After reaching the target temperature, a portion of each sample was removed at 2-hour intervals throughout the 8-hour work day. It would have been nice to continue past 8 hours, since that’s really not very long in the oil analysis world, but fear of burning down the lab kept us in line. And once we took the first 392°F sample (see Image 1), our fears were vindicated.

The most obvious change we noticed was color. Image 2 shows that heat alone caused the oil to darken over time, and you can even see a color change between 302°F and 392°F, in Figure 3 below. So something is definitely happening as the oil gets hotter, but does it affect the TBN?

Once all the samples were collected, we tested the TBN, TAN, and viscosity, with the results shown in Figure 1. Eight hours at normal operating temperature had virtually no impact, and even at a relatively high 302°F, the TBN only dropped slightly over time. At 392°F, however, the TBN took a nosedive. By the 4-hour mark, it was already down to 1.8 — low enough that we wouldn’t suggest running the oil any longer — and it kept going down from there.

Even though this is a small sample size, the data clearly shows that high temperatures do cause the TBN to drop more rapidly, and the effect is more pronounced as time passes. Heat is far from the only factor impacting active additives out in the real world, where the oil also has to deal with the negative effects of friction, contamination, and fuel blow-by, just to name a few. But it doesn’t seem farfetched to think some of the damage from overheating could be linked to a diminished capacity to neutralize acids, so the TBN might be worth tracking in those instances when oil temps end up off the charts.

Surprising Finds
It’s worth noting that the TBN fell without throwing the viscosity out of whack — even the 8-hour sample at 392°F, the only one that ended up obviously thicker, was still within the normal range for 15W/40 (12.7 to 15.8 cSt at 212°F). We typically associate a thicker viscosity with “heat damaged” oil, but except in extreme circumstances, it looks like that viscosity increase is likely due to other factors, like high friction causing a breakdown of viscosity-improving additives, rather than just the heat itself.

Another surprise was that the 392°F samples also had a noticeably lower TAN reading. If you remember from the previous newsletter, the TBN tends to go down the longer the oil is used, and the TAN tends to increase, so at first this seems like a really weird result. What’s going on here?

Well, it’s important to remember that the TBN and TAN tests technically measure two different things. The TAN is a measure of how acidic the oil is, while the TBN measures the oil’s capacity for neutralizing acids. It appears that the excess heat has caused a chemical reaction that caused the oil to become less acidic while at the same time reducing the oil’s capacity to neutralize acids, likely by damaging the TBN-boosting additives or causing them to fall out of suspension. If this were a real used oil sample, acids would also be building up due to the other factors in the engine we mentioned above (contamination, blow-by, etc.), causing the TAN to increase. But since this was a controlled experiment where heat was the only variable, that didn’t happen here.

A Colorful Surprise
Before we end: a mystery! While we researching this article, we got curious about Aeroshell 100 Mineral oil. In theory, this type of oil shouldn’t have any additives at all (the normal additives in automotive oil can cause catastrophic detonation in aircraft engines), so we wanted to confirm that this oil would start out with a 0.0 TAN (it did) and a low TBN (also true at 0.0).

What we weren’t expecting was for the titration solution to turn bright purple! Usually samples stay evenly light yellow throughout testing, but once the basic solution (potassium hydroxide and isopropyl alcohol – the “Bruce” from Part 1) was added to this sample, the color drastically changed. A few minutes later, it began changing back to yellow and you can see that process beginning in Image 4. This made us even more curious, so we found a bottle of Aeroshell W100 (which does have some ashless-dispersant additives) and measured its TAN and TBN as well. They were 0.0 and 0.2, respectively. And lo and behold, this sample took on the same cheery magenta once the basic solution was added.

We aren’t sure why this happened, but we have a guess. Phenolphthalein is a pH indicator used in some other sorts of acid-base titration. It turns purple in basic solution, in the same way litmus paper turns blue. Phenolphthalein won’t show up in our spectral exam, since it’s made of the same elements as oil (C20H14O4), but maybe it or another pH-sensitive substance is present in these oils? We’re not sure! If you know the answer, we’d love to hear from you at bstone@blackstone-labs.com.

Answering the question! So, back to the main question — Do you need a TBN or TAN? The results of our experiments suggest that these tests can be helpful, especially if your engine oil got much hotter than it should. If you’re not having a problem with temps though, the main reason to get a TBN is what we discussed in Part 1 — seeing if the oil can be run longer.
In either case, the TBN or TAN readings provide additional data points, but they don’t replace the information on wear levels and physical properties found in the standard oil tests. Whether you’re concerned about heat damage or just looking to run a few thousand miles longer on the next oil, we look at all of the data to answer your questions and give you a complete picture of the engine’s health.

By Suzanne Herman|2025-02-11T10:15:22-05:00February 11, 2025|Articles, Gas/Diesel Engine|Comments Off

TBN/TAN: Do You Need One?

“Do I need a TBN?” It’s a question that comes up a lot. The TBN is a test we do on engine oil, while the TAN is meant for transmissions and other gear lubes or hydraulic oils. These tests are widely discussed on internet forums, where facts and misconceptions can be hard to distinguish. So let’s dig into the science behind them!

What is a TBN or TAN?

The Total Acid Number and Total Base Number are ways to determine how acidic oil has become (TAN), or how effectively it can neutralize the acids that form from combustion and other factors (TBN). An increasing TAN indicates more acidity, while a decreasing TBN shows an oil’s acid-neutralizing additives are being used up. You may remember the pH scale from science class. pH is a more familiar measure of acidity in everyday life. So why don’t we use pH on oil?

pH stands for “potential of hydrogen” and measures the flow of hydrogen ions in a water-based solution. pH doesn’t apply to oil because these ions can’t flow through oil – it’s a poor conductor. That’s why oil is used as an insulator for transformers and other applications that call for interrupting the flow of electrical current. Fortunately, we can use titration to get around this obstacle. Titration is used to determine the concentration (in this case, the acidity level) of an unknown solution (oil) by exposing it to measured quantities of a known solution (acid or base).

Running the tests

We start by mixing one gram of oil with a happy blend of toluene, chloroform, isopropyl alcohol, and a splash of H₂O. (Kids, don’t try this at home!) The solvent breaks down the oil into a solution that is a better conductor, so we can measure the pH. The next step differs slightly for the TAN or TBN.

For the TAN, we add a cocktail of chemicals – let’s call it Bruce – to the toluene solution, a little at a time. This continues until the pH reaches 11. The lab techs then use an equation to calculate the TAN from the amount of Bruce added to the oil-toluene blend.

The TBN follows a similar methodology, except the solution added is more acidic – more of a Boris than a Bruce.

The end goal for the TBN titration is a pH of 3, and as with the TAN, the lab people are doing some math to transform the amount of Boris added to the oil into your TBN number.

Why get a TBN?

As the oil circulates through the harsh environment of a hot, running engine, combustion causes acids to form. These acids can cause increasing wear and corrosion. To prevent this, the oil manufacturers add detergent additives to the oil, which help it buffer those acids and stabilize the oil’s pH. The higher the TBN, the better your oil can resist becoming acidic. That’s the main reason to check the TBN. It’s a helpful data point if you want to extend your oil change interval beyond manufacturer recommendations.

The TAN does essentially the same thing, but we use the TAN on oils that don’t have detergent additives (like hydraulic oil and ATF). Some industrial equipment manufacturers will set standards for when to change the oil based on the TAN.

Which oil has the highest TBN?

The TBN is mainly based on the amounts of calcium and magnesium (detergent additives) in the oil. Oils with more of those additives typically have a higher starting TBN, and those with less will rank lower on the list. Is more better? Not necessarily (and we’ll get into that a little later). Meanwhile, Figure 1 lists a slew of virgin engine oils and their average starting TBNs, from highest to lowest. The progression isn’t perfectly consistent, because we don’t test for every conceivable substance the oil manufacturers might include that determines the TBN. chart showing the TBN for various types of oil

As you probably know, the TBN drops pretty fast when you start using the oil. Then it levels out and drops more slowly, the longer the oil is run. Figures 2 and 3 show two types of Mobil and how the TBN tends to fall as acidic substances start to “use up” the detergent additives. That’s what they’re there for, and we consider any TBN over 1.0 sufficient, while a TBN of 2.0 or greater is ideal when choosing to run the oil longer than you currently are. Note that ppm calcium and magnesium stay roughly the same – it’s their ability to neutralize acids that decreases.

chart showing the TBN and TAN of Mobil 1 5W/30 at various mileage intervals

Figure 2: This oil has an average starting TBN of 7.5. Note the roughly inverse relationship of the TBN and TAN readings; as the TBN decreases, the TAN increases, as less “active additive” is available to neutralize acids.

chart showing the TBN and TAN of Mobil 1 Annual Protection 0W/20 at various mileage points

Figure 3

Figure 3: This oil has an average starting TBN of 7.9. The chart shows the same fairly predictable drop in TBN as miles increase. Interestingly, the TAN is less predictable, probably due to factors outside the scope of this newsletter.

Is more better? A look at two novel blends

It’s easy to see how you might feel like you want an oil with a starting TBN that’s as high as possible. But Figure 1 makes it clear that oils with all sorts of starting TBNs are available. Did the manufacturers at the low end of the scale just cheap out on additive? Not at all. Oil manufacturers have to cater to an array of unique engine designs, operating conditions, etc. As technology evolves, so does oil.

Joe Gibbs

See, for example, Figure 4, which lists a few different samples of Joe Gibbs Driven D140 oil. It had the lowest average starting TBN (4.4) thanks to fairly low levels of calcium and magnesium. This left the TBN between 2.0 and 1.0 after just 5,000-6,000 miles. But the engine that produced those numbers was a Porsche 911 that had excellent wear trends (see Figure 5). This oil is specifically formulated with lower calcium and higher moly to combat low speed pre-ignition and reduce abnormal combustion and wear. While we can’t say whether this oil really does reduce LSPI, it seems to work as well as others do and we see no problems with the novel additive blend.

Figure 4

Figure 5

Figure 5: Wear trends for the five samples in Figure 4 (and one additional sample, not included there because TBN and TAN were not requested). Wear is consistent over time and compares favorably to averages, despite the low TBNs.

Chevron Delo

Chevron Delo 600 ADF is another oil that breaks the traditional additive mold, and it’s fairly new to the market. The 15W/40 and 10W/30 formulations hold the 2^nd and 3^rd place spots for lowest starting TBN in Figure 1, which is surprising, since they’re formulated for diesel engines – diesel oil tends to have more dispersant additive than oil designed for gasoline engines (most of the oils in Figure 1 are gas engine oil). Figure 6 shows the Delo 600’s TBN reaching our “1.0 limit” starting around 9,090 miles. Chevron also had particular goals in mind for this oil – it uses “ultra-low ash additive technology” and is meant for engines with SCR and EGR emissions systems that need to meet state emissions standards.

Figure 6

Figure 6: This oil had an average starting TBN of 4.7. The chart shows the low levels of calcium and magnesium that resulted in fairly low TBNs after typical oil runs for diesel engines.

Since additive packages tend to be proprietary and Chevron never did respond to my email, we can only speculate as to how the elements we find in our testing relate these constraints. Maybe such low calcium and magnesium reflect a reduction in calcium sulfonate and magnesium sulfonate (the compounds that register as calcium and magnesium). While these compounds work well as detergent/dispersants and their alkalinity helps buffer acids, their presence would also boost the sulfur content – a potential problem for emissions goals. But the additive package is unique in other ways too.

Oil report for a virgin sample of Chevron Delo 600 ADF 15W/40

Figure 7

Figure 7 is a virgin sample of Chevron Delo 600 ADF 15W/40. Note the high levels of molybdenum, potassium, and boron, and low levels of phosphorus and zinc, in contrast to the more typical additive package shown in the universal averages column. Moly seems to be providing most of the anti-wear properties that phosphorus and zinc ordinarily would. Potassium is noteworthy and caught our attention right away, since it’s one of two potential markers for anti-freeze.

We’re not certain what additive compound registers as potassium in this oil, but because potassium is alkaline, perhaps it performs some of the same functions calcium sulfonate and magnesium sulfonate do in more traditional additive packages.

Interestingly, even when potassium (and sodium, which is also alkaline) is truly from coolant contamination, it can skew the TBN. Figure 8 is an example of an engine suffering from coolant contamination, which is taking a heavy toll on the bearings and physical properties of the oil. An oil change (and probably major repairs) are needed, yet out of context, the 10.0 TBN looks great. But that doesn’t mean the oil is ready for more use; rather, coolant is skewing the reading. That’s why we never judge a used oil sample by a single data point!

Oil report for a used sample of Valvoline 10W/30

Figure 8

Figure 8 shows a sample of Valvoline 10W/30, which has an average TBN of 7.2 out of the bottle. The oil was used 3,000 miles in an engine with a major coolant problem, seen in very high levels of potassium and sodium, a thick viscosity, high insolubles, and high wear levels. The TBN is very high at 10.0, but that doesn’t mean the oil is ready for more use; rather, coolant is skewing the reading.

As for Chevron 600 ADF? The jury is still out on what kind of results this oil will produce over time, since most of the samples we’ve tested so far are from young engines going through wear-in. It will be interesting to see how these engines mature, but we suspect in the end, this unique oil will perform as well as any other in the most crucial ways: lubricating, cleaning, and cooling engine parts. We’ll just have to give it some special treatment on our end, to avoid false positives for anti-freeze, and avoid putting too much stock in “low” TBNs.

We hope you’re walking away armed with knowledge and a pretty good idea whether adding a TBN or TAN is going to serve your particular aims. If you’re wanting to extend your oil changes, go for it! If you just want a basic assessment of how your engine and oil are holding up, not to worry! We can provide that with the core tests in the standard analysis. Stay tuned for Part 2 next newsletter, where we venture into the lab, and learn about the effects of heat on TBNs and TANs.

By Suzanne Herman|2024-09-19T09:13:00-04:00July 28, 2023|Articles, Gas/Diesel Engine, Lab Tests|Comments Off

What’s the Best Oil Change Interval?

Here’s an interesting question we received recently from Pete, one of our long-time customers:

“Needed to ask you about AMSoil OE synthetic oil. The change interval that is suggested for that oil is whatever the vehicle manufacturer has specified for that particular vehicle. But what have you seen from the TBNs that you have run on that oil? It doesn’t make sense that in my old 01 Maxima it would only be good 3000 miles but in a brand new vehicle it could be good for 10K.”

Pete has a point. Why would the same oil wear out faster just because the manufacturer recommends a shorter oil change interval? If the oil can hold up for 10,000 miles or more in some engines, shouldn’t it be able to do so in any type of engine?

Of course, there are some reasonable explanations that Amsoil (or any oil manufacturer) might give for this. The industry is generally moving towards longer oil change recommendations because modern engines are built to more exacting standards than they were even ten years ago, allowing for improved efficiency and less damage to the oil.

Plus, you might have to adjust the oil change interval in the same exact engine based on whether you’re seeing “severe” duty or not, so it’s probably reasonable to think that some types of engines would just treat the oil a little more harshly, and require a shorter oil run, right?

The cynical side of me, though, says that the real answer to this question probably has more to do with the legal department than the oil’s engineers. Regardless of how good you think your oil is, if you start telling customers they can ignore the original engine manufacturer’s recommendations, you’re probably opening yourself up to some legal headaches that the head office just doesn’t want to deal with.

But true as that may be, it’s not a very good answer for Pete, or the rest of our customers who are just looking for the best advice on how to treat their vehicles. So setting aside specific recommendations for a moment, let’s get to the nut of Pete’s question… Does the life expectancy of the oil change based on what engine it’s used in?

The tale of the TBN

There are several factors that we use to determine if your oil can be run longer, but Pete asked specifically about the TBN, so let’s focus on that for now.

For those who don’t know, the TBN (Total Base Number) measures the amount of active additive remaining in the oil. A typical gasoline-engine oil might have a starting TBN between 6.0 and 8.0, while diesel-use engine oils tend to have higher TBN’s of 11.0 or 12.0, since they have to deal with dirtier, more acidic conditions.

But regardless of where a TBN starts, they all end up in the same place—0.0—if the oil is run too long. Once the TBN is down to zero, it means that the oil is no longer able to neutralize acids produced by the engine. As a general rule of thumb, we usually say that once a TBN gets lower than about 2.0, it would probably be a good idea not to run the oil much longer, to avoid running out of those active acid-neutralizing agents.

To answer Pete’s question about how the TBN of Amsoil OE holds up in different engines, we searched our database to find the recent TBN results we’ve seen from that type of oil. Since the TBN is an optional test, we don’t run it on every sample we see, but customers who use Amsoil tend to be pretty interested in seeing how long they can run their oil, so we have a pretty good representation for that oil type. We plotted nearly 50 samples’ TBN results against the mileage on the oil, and came up with this graph:

The banana-shaped line we’ve drawn approximates the “average” TBN for this type of oil over a given mileage. You can see that the TBN tends to drop quickly at first, but the longer the oil is run, the slower the TBN drops. Of the samples we tested, none of them had a TBN less than 1.5, so even on very long oil change intervals, this Amsoil OE oil tends to retain plenty of active additive.

Also note that the actual test results (the dots) can stray pretty far from that line on either side, so even though the TBN readings tend to follow a particular pattern, there can be a pretty wide deviation in individual test results. Just at a glance, you can easily see that the sample with the highest TBN reading didn’t have the lowest mileage on the oil, nor did the sample with the longest oil run (a whopping 18,500 miles) have the lowest TBN reading. In fact, the lowest TBN came after a fairly middle-of-the-road 8,569-mile oil change interval.

And before we get too hung up on looking at just Amsoil OE, we ran the same analysis for one of the most common oil types we’ve tested, Mobil 1 5W/30, resulting in the following chart:

The graph for Mobil 1 5W/30 covers nearly 5,000 samples with TBNs, and the scale is a little different than the Amsoil OE chart, but you can see that banana-shaped curve that we’ve drawn, approximating the average TBN for a given mileage, is exactly the same as in the Amsoil OE chart. Once again, the highest TBN was not the shortest oil run, and the lowest TBN was not the longest oil run. So even though we have many more TBN data points for Mobil 1 as we do Amsoil OE, the overall trends for TBNs are similar, and would be with just about any type of oil you could name.

What affects the TBN?

So what other factors might be affecting the TBN? To find out, we ranked all the samples according to both mileage and TBN reading, and came up with the best and the worst of the bunch.

One factor that definitely stood out was make-up oil. If you add some fresh oil in between oil changes to top up your oil level, you’re infusing the oil with more active additives, and diluting wear metals and contaminants at the same time. That’s why we often say that you shouldn’t be too upset about adding a quart or two of oil over the course of your regular oil interval (assuming you don’t have a noticeable leak, of course), since that fresh oil might buy you a few thousand extra miles before you have to do a full oil change.

In this case, all of the samples that noted adding a quart of oil or more ranked in the top half of the results, and the Amsoil samples with the most oil added (2.5 and 3 quarts) ranked at numbers 2 and 7, respectively. On the other hand, the overall best-ranked sample, with a TBN of 4.0 after 10,000 miles, didn’t add any oil in that time, according to their oil slip, so make-up oil alone is not the only relevant factor.

Pete’s original question was about manufacturer’s recommended oil change intervals. We don’t have a list of the recommended OCI for every engine we’ve tested, so we’ll have to settle for looking at some other factors, like the age and size of the engine.

For both the Amsoil and the Mobil 1 samples, the age of the engine didn’t seem to make much of a difference. We had engines from the late 90’s and early 2000’s in the top ten percent on both charts, mixed right in with new engines from the last few model years. The total engine mileage was also mixed, with higher-mileage engines ranked right alongside brand new engines in their first few oil changes.

Engine size is one factor that I thought would end up playing a pretty big role, but I wasn’t sure which way it would go. On the one hand, larger engines tend to work harder, so I wondered if the larger 6-cylinder engines and big V8s might burn through the active additive more quickly than smaller engines. On the other hand, 4-cylinder engines also tend to have smaller oil sumps, meaning less total oil volume in the engine, so maybe their active additives get used up sooner.

Mixed results

Turns out there results were pretty mixed as well… there was a bit of a trend for smaller engines to hold a higher TBN for longer oil runs, but there were plenty of larger engines near the top ranks of both lists, and vice versa. Seems like the extra oil in the sump of the larger engines pretty much balances out the extra work they have to do, resulting in a mostly even distribution of engine sizes across the rankings in both charts.

So what does all this tell us? Well, at least as far as the TBNs go, it doesn’t look like the type of engine has much of an influence on how long the active additive lasts in the oil. Engines of the exact same type (and in some cases, even the exact same engines) were ranked both high and low in our results, so it looks like individual driving habits and the behavior of each particular engine play a much larger role than engine sizes, model years, manufacturers, or any other criteria we could see.

When you get right down to it, though, the TBN is only one factor in determining whether or not it’s safe to run the oil longer. It’s a valuable tool, but we also have to look at other factors, like wear metals, insolubles, viscosity, and contaminants, any of which could indicate that you shouldn’t run the oil any longer, even if the TBN is still good.

The bottom line is this: the lawyers have to tell you to follow the engine manufacturer’s recommendations, since they have no idea what’s going on with your particular vehicle. And really, the original engine manufacturer doesn’t have much better of an idea—they know how their engines should wear, and base their recommendations on what should work best for most drivers, but they don’t have any idea about your particular driving habits or maintenance routines.

When you get your oil analyzed at Blackstone, we’re looking at the specific conditions for your specific engine, which is why we can tell you if it’s safe to add an extra 2,000 or 3,000 miles on your next fill, regardless of your current OCI. Just check “Yes” next to the question “Are you interested in extended oil use?” on the back of your next oil slip, and maybe you too will be free to explore the world of extended oil use!

By Travis Heffelfinger|2024-09-19T10:05:06-04:00July 28, 2023|Articles, Gas/Diesel Engine, Marine|Comments Off

Do I Need a TBN?

What is a TBN, and who uses it? In short, a TBN (Total Base Number) measures how much base (as in base vs. acid) additive is in the oil to offset the effects of acids coming into the oil from combustion and other sources. Scientifically speaking, the TBN is one of two “neutralization number” tests run on oils. The TAN (Total Acid Number), which is used for hydraulic and gear oil, is the other. The TBN test is useful for anyone who wants to extend their oil use beyond the normal range.

The oil’s function is to lubricate, clean, and cool the engine. Additives are added to the oil to enhance those functions. The TBN will start out reading in the 6.0 to 14.0 range (depending on the oil and whether it’s meant for gas or diesel engines). When you first start using the oil, the TBN tends to drop sharply. Then it levels out and drops more slowly after that. The lower the TBN reading, the less active additive the oil has left. A low TBN test result, meaning very little additive is left, is down around 1.0 or lower.

The TBN is not the only factor to consider when determining how long an oil can be used. If wear accumulations and insolubles in the oil build up and become abrasive, we would recommend changing out the oil, no matter how high the TBN reading.

We offer a TBN test on any gasoline or diesel oil sample for an additional $10. Note: You do not need to send in a virgin sample for us to run a TBN on your oil. Some people like to know where the TBN starts out in virgin oil, and of course we’re happy to test that for you if you’d like. The cost of a virgin oil sample plus TBN is the same as a regular oil sample plus TBN.

By Jim Stark|2024-09-19T10:23:17-04:00July 12, 2023|Articles, Gas/Diesel Engine, Lab Tests, Marine|Comments Off