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THE OIL BAYExcerpts from Truck Parts & Service magazine July 1998One of the most important decisions you have to make for your customer is selecting the right oil for the engines of today. Contrary to what some believe, oil from one manufacturer is not exactly the same as oil from another. The additives and makeup of various oils can differ, especially when it comes to the Total Base Number (TBN) of the oil. Is a high TBN really necessary and just how critical is that number? What is TBN? TBN is the measure of an oil’s ability to neutralize the acids resulting from combustion. In fact, Shell says, TBN in new oil TBN is less important than the TBN level during service, this indicates how well the oil is protecting the engine. A high oil TBN does not guarantee that it will retain this level during service. New oils with a lower TBN actually may maintain TBN better. In either case, regular oil analysis is the best way to know you’re using the right oil. TBN is not a measure or guarantee of an oil’s performance. Things to know about TBN: how it is measured, and the rate at which it depletes. Let’s start with methods of measuring TBN. The American Society of Testing Materials (ASTM) has three acceptable methods for measuring TBN. Experience over many years of engine testing shows that the ASTM D2896 test will produce a higher TBN rating and the D4739 test will result in the lowest number. The company says most people use the D2896 to test new oils. “We believe that, especially when testing used oil, D4739 results are more reliable because this method more accurately reflects the level of neutralizing power left in the oil after use,” Shell notes. Most used oil analysis programs use the D2896 method unless another test is requested because it’s easier and faster to run. If your customer is trying to extend oil drain intervals---then D4739 is a more valuable test because it gives a more accurate indication of oil serviceability. Shell suggests you instruct the oil analysis lab to use the D4739 test. The second important feature of TBN, more critical than how highly it’s rated in new oil, is the rate at which it depletes during use. Some oils start with a high TBN, then drop and lose their neutralizing ability quickly. Naturally, what’s important is how well an oil can maintain a good TBN during service. The real value of a TBN number, Shell explains, is not determining an oil’s quality; it’s in making sure an oil is not becoming corrosive before it is drained out of the engine. |
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