Choosing Oil Based on TBN Number. It’s Not That Obvious.

TBN (Total Base Number) is an indicator of the content of basic chemical substances in engine oil. As engine oil additives evolved, TBN value treated as a single reference point is no longer as significant as it was a dozen years ago. Mobil experts emphasize that more important than relying on a high TBN is finding a product that is least susceptible to a drop in alkalinity between oil changes. This position is supported by the results of laboratory tests of lubricant formulations.

TBN has a significant impact on engine protection when diesel oil contains high levels of sulfur. Its presence causes several negative consequences for the engine, such as clogging the catalyst and accelerating corrosion. With the introduction of successive Euro standards, the maximum sulfur content in diesel and gasoline was limited to 10 ppm (parts per million). For comparison, the Euro I standard allowed 200 times higher sulfur content in fuel, which greatly influenced the control of acid combustion product neutralization by engine oil.

However, even today, when we use more advanced lubricant formulations and fuel blends, the TBN number in oil still plays an important role in acid neutralization, preventing deposit formation, and hence in extending engine life. Basic chemical substances can effectively dissolve deposits and maintain cleanliness of engine components such as pistons, rings, and valves. A clean engine runs more efficiently and provides better lubrication. Basic additives in Mobil engine oil create a protective layer on metal surfaces, reducing friction and wear. They also protect against corrosion, especially in engines operating under harsh conditions, such as in utility vehicles used off-road and exposed to extreme temperatures.

“Advancements in the development of engine oil formulations have led to modern additive packages significantly slowing down the degradation of the lubricant. Consequently, the TBN number of new engine oil can decrease more slowly between changes. Tests conducted by ExxonMobil have proven that a high TBN number of new oil is not a guarantee that this oil will effectively neutralize acidic combustion products until the next change,” says Esin Yilmaz, Technology Solution Professional, ExxonMobil.

The graph below shows how TBN decreases over time while the total acid number TAN increases. The test was conducted using the Mack T-12 engine, in accordance with ASTM D 4739 standard, and included three engine oils: Mobil Delvac XHP ESP 10W-40 and two competitive Full SAPS oils with standard ash content.

Despite having a significantly lower TBN, Mobil Delvac XHP ESP 10W-40 maintained better alkalinity for the engine until the end of the test, keeping a higher reserve for neutralizing acids. Its advantage over competing Full SAPS oils was in its better ability to maintain the total base number after several hundred hours of engine operation.

Low-ash Mobil Delvac engine oils are specially formulated to maintain the reserve of neutralizing acids and ensure excellent engine protection, thus extending oil change intervals, even compared to some high-ash product offerings. At the same time, it is essential to remember that undue importance should not be attached to the TBN value of new oil. In practice, it is not the value itself, but the formulation’s ability to sustain TBN that will provide benefits for our engine.