What is the TBN ?

Total Base Number (TBN) is one of the most important indicators of an engine oil’s quality and performance. It represents the oil’s ability to neutralize acidic by-products that are formed during fuel combustion. Measured in milligrams of potassium hydroxide (mg KOH) per gram of oil, TBN tells us how much alkaline reserve is available in the lubricant.

In simple terms, higher TBN = stronger protection against acidity.

Why is TBN Important?

During engine operation, fuel combustion produces sulfur oxides and nitrogen oxides, which react with water to form strong acids. If not neutralized, these acids attack metal surfaces, leading to:

• Corrosion of engine parts

• Increased wear

• Oil degradation

• Reduced engine life

The additives in engine oils—especially detergents and dispersants—provide alkalinity to neutralize these acids. TBN measures how much of this reserve is present.

Balancing TBN with TAN

While TBN measures alkalinity, Total Acid Number (TAN) measures acidity. Both are important:

• High TBN, Low TAN → Oil still protective

• Low TBN, Rising TAN → Oil is exhausted, needs changing

• Imbalance can cause either corrosion (low TBN) or deposits/ash (excessively high TBN)

  • TBN is a measure of an oil’s ability to neutralize acids.

  • It is crucial for preventing corrosion, wear, and premature oil breakdown.

  • Monitoring TBN (together with TAN) in oil analysis helps determine safe oil drain intervals.

  • Choosing the correct TBN oil depends on engine type, fuel quality, and operating conditions.

    While TBN measures alkalinity, Total Acid Number (TAN) measures the buildup of acidity inside the oil.

    • TBN starts high and decreases over time as the additives are consumed.

    • TAN starts low and increases over time as acidic by-products accumulate.

    The critical point is when the two curves intersect (TBN = TAN). This intersection represents the moment when the oil has lost most of its protective ability, and it is considered the optimal time to change the oil.

    Using the TBN vs TAN relationship is one of the most reliable ways to determine oil drain intervals in

    Typical TBN Values Range

    • Passenger Car Engine Oils: Usually between 6 – 11 mg KOH/g

    • Heavy-Duty Diesel Oils: Higher, typically 8 – 14 mg KOH/g, since diesel fuel generates more acids

    • Marine & Stationary Engines: Can exceed 70 mg KOH/g, due to high-sulfur fuel usage