TBN (Total Base Number) and TAN (Total Acid Number)
The combustion process in the engine creates acid in the oil. TBN and TAN are a measure of the acid in the lubricating oil.
TBN seems to be used for diesel engines and TAN is used for gasoline engines. While the numbers are opposites, they measure the same thing, acid in the oil. TBN starts at 8.0 and could be higher depending on the chemical formulation of the oil, TAN starts at 0.0.
As the combustion process takes place, the base becomes more acidic and the TBN number drops. Correspondingly with TAN, as the oil becomes more acidic the number increases. The higher the TBN the better, the lower the TAN the better.
Total Base Number.
Testing a lubricant’s base number measures its alkaline reserve – or its ability to neutralize degradation acids. Although viscosity is more important, base number determines an oil’s suitability for continued use and is critical to safely extending drain intervals. A decrease in base number is typically accompanied by an increase in oxidation, nitration and viscosity.
Sulfur from fuel and nitrogen from the air – when combines with water – form sulfuric and nitric acids that will attack engine metals causing wear that can eventually result in engine failure. To combat combustion byproduct acids, diesel engines oils contain acid neutralizing additives – the most common being magnesium and calcium.
New diesel engine oils typically have a starting base number between 8 and 12. It is generally recommended that diesel engine oil be changed when the Total Base Number is 50% that of the new oil. For example, an engine oil with a starting base number of 10 should be changed if the base number test result is less than 5.0 mg KOH/g.
Total Acid Number.
Engines fueled by natural gas operate at higher temperatures than diesel engines requiring lubricating oils with lower ash content. Higher temperatures cause metal sulphates in barium, magnesium, calcium and phosphorus-based additives to form engine deposits. These ash deposits then cause valves to stick reducing engine efficiency. In addition, excessive concentrations of ash can form in glassy deposits on natural gas engine exhaust catalysts reducing their ability to control harmful emissions.
Typical low ash natural gas engine oil has one third the amount of detergent and one fourth the amount of anti-ware additives as diesel engine oil which leaves them as vulnerable as diesel engines to the degradation acids produced by combustion. Testing for acid content and monitoring the rate at which these acids form become the objective in determining a natural gas engine oil’s suitability for continued use or safely extending drain intervals. An increase in acid number is typically accompanied by an increase in oxidation, nitration and viscosity.
The starting acid number of new oil is determined by the amount of acid present from additives. Typical new low ash or ashless natural gas engine oils have a starting acid number between 0.7 and 1.0 mg KOH/g. The general recommendation is to change the oil when the acids number is four times the acid number of the new oil. For example, a natural gas engine oil with a starting acid number of 1.0 mg KOH/g should be changed when the acid number test results is 4.00 mg KOH/g or greater.
TBN/TAN Oil Analysis Report.
The oil analysis information on a 2007 Honda Accord with a V-6 engine follows.
When purchased the vehicle had been serviced with Mobil 1 5W-20. Oil analyses were done when the in-car computer determined oil change was needed based on starts/stops/etc. The first oil analysis with Mobil 1 was to establish a base line for further comparison. The second oil analysis was with Mobil 1 and 10% DSX Extra. The third, fourth and fifth oil analyses were done with Kendall 5W-20 Blend and 5% DSX Extra.
The important information is in the wear factors and the TAN. Note. The last oil analysis was done based on a scheduled service, not the usual computer determination. We understand that this is a gasoline engine, not a diesel engine. However, wear is still wear and acid is a function of the combustion process.
We have limited multiple oil analyses on diesel engines with TBN reported, because much of what we did was with a Caterpillar facility.
Example 1.
TBN. One engine with DSX Extra in the engine oil a sample was taken half way through the first service cycle and the TBN was 5.9. Halfway through the second service cycle with DSX Extra in the engine oil, the TBN was 7.1. Remember the higher the TBN the better. These results indicate that less acid was being made during the combustion process. Unfortunately, we did not get a sample of the oil from the used oil prior to the first service cycle with DSX Extra. Note. The person changing the oil for this company of 100+ trucks comments several times that he oil after using DSX Extra was cleaner, looked better and did not smell burned.
Example 2.
TAN. Personal vehicle with gasoline engine. I obtained oil samples from my Volvo wagon with 187,000 miles of use (140,000 with DSX Extra) and another newer Volvo with the same engine but only 42,000 miles. The oil samples were obtained from my Volvo dealer. The oil was Castrol Synthetic Blend. The oil from my car had 6,200 miles on it. The oil from the newer Volvo had 5,400 miles on it. The TAN for the oil from my Volvo was 2.8; the TAN for the newer Volvo (42,000 miles on the car and 5,400 miles on the oil) was 4.2.
Example 3.
TAN. Personal vehicle with gasoline engine. I sent an oil sample from my Honda for analysis. The oil was Mobil 1 – Synthetic. DSX Extra was not added tot eh Mobil 1 at this time. The oil had 6,430 miles on it. The TAN was 2.8. DSX Extra was added to the Mobil 1 Synthetic for the next service cycle. The next oil sample had 6,479 miles when sent to the laboratory. The TAN was 2.0.
Conclusion.
Although we have limited data at the moment, all the data points out that with DSX Extra in the engine oil, there is less acid build up so there is less potential damage to the engine and the service cycles can be extended.
Viscosity.
In all three cases mentioned above, the Viscosity was higher as reported in the oil analysis report after using DSX Extra.
IMPORTANT.
This information supports the idea that service cycles can be extended, although we do not take the position that by using DSX Extra, you can extend a service cycle.
It is important that the benefits of using DSX Extra are understood and that any decision to extend a service cycle should be based on the oil analysis obtained on your own vehicles, rather than a report generated by us as informative information.
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