- Total Base Number
**Total Base Number**(**TBN**) is a measure of alubricant 's reservealkalinity . It is measured in milligrams ofpotassium hydroxide per gram (mg KOH/g).TBN determines how effective the control of acids formed will be during the

combustion process . The higher the TBN, the more effective it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time.The associated measurement ASTM D2896 and ASTM D4739-06 generally range from 6-80mg KOH/g in modern lubricants, 7-10mg for general automotive use and 10-15 for Diesel operations.

Marine grade lubricants generally will run from 15-50mgKOH/g, but can be as high as 70 or 80mg KOH/g as is the case of Exxon’s MobileGuard 570 or respectively Castrol’s Cyltech 80AW this high level is designed to allow a longer operating period between changes, under harsh operating conditions. When the TBN is measured at 2mg KOH/g or less the lubricant is considered inadequate for engine protection, and is at risk for allowing corrosion to take place. Higher sulfur fuel will decrease the TBN faster due to the increased formation of

sulfuric acid .**Additional information****TAN**(Total Acid number) is the inverse measurement of TBN. It is covered under ASTM D 664 and refers to the level of acid contamination caused by combustion.**References*** [

*http://www.astm.org ASTM International*]

* [*http://www.noria.com/learning_center/category_article.asp?articleid=100&relatedbookgroup=Lubrication2 Noria Learning Centre article on TBN & TAN*]

* [*http://www.amsoil.com/performancetests/g1971/index.aspx Amsoil Comparative data*]

* [*http://www.exxonmobil.com/USA-English/Marine/PDS/GLXXENMRNEMMobilgard_570.asp Mobileguard 550 Product Description*]

* [*http://www.castrol.com/castrol/multipleproductsection.do?categoryId=4504559&contentId=57476 Castrol Cyltech 80AW data*]

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