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The Importance of Total Base Number

When selecting your engine oil, there are many things to consider due to the fact oils must function well to lubricate, cool, and clean the engine. Total Base Number (TBN) is a property that measures oil’s ability to neutralize acids formed during engine operation. Generally, oils with a higher TBN better neutralize acidic materials and combustion by-products resulting in longer oil life and improved protection against corrosion.  Since TBN measurements are typically used as an indicator of the lubricants capacity of how much additive is left to neutralize acids, they are especially useful when operators want to extend their drain intervals.

Diesel engine oils are normally formulated with a higher TBN to protect against the formation of acids caused by incomplete fuel combustion. The TBN of fresh oil is typically in the range of 7 to 10 for gasoline engines and 10 to 14 for diesel engines. If the TBN drops to a point where the oil can no longer neutralize acids, usually around 3, it typically indicates it is time for an oil change.

The most common causes for a TBN drop are oil oxidation and low quality fuel with high levels of sulfur. Oil oxidation occurs naturally over time and can commonly be observed in extended drain interval situations. It is also related to operating temperatures.  Oils exposed to higher operating temperatures, especially engine overheating, oxidize more quickly.  Low quality fuel with higher sulfur content also depletes TBN.  Sulfuric acid formed during the combustion process is neutralized, leading to a corresponding drop in TBN.  

TBN is just one of many engine oil parameters important to engine durability and extended service intervals. The best way to know if your lubricant is doing the job is through use of oil analysis.  As part of a routine maintenance program, oil analysis can help establish safe and proper drain intervals.  Tests of the used oil’s physical properties can identify wear metals or contaminants like antifreeze or dirt before any permanent damage is done.

See your FS Energy Specialist for information on how engine oil analysis can work for you.  You will rest easier knowing that you are establishing change intervals that reduce unforeseen issues, breakdowns, and downtime, while extending equipment life.  You’ll even be confident that today’s lower viscosity oils formulated to improve fuel economy are continuing to provide the wear protection you need. 

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