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What are acceptable values for used oil analysis?

Typical acceptable values for continued use of a gear oil are:


Viscosity: AGMA 4 (ISO 150) – greater than 135 cSt and less than 165 cSt at 40°C

                AGMA 5 (ISO 220) – greater than 198 cSt and less than 242 cSt at 40°C

                  AGMA 6 (ISO 320) – greater than 288 cSt and less than 352 cSt at 40°C

Water Content:         less than 400 ppm

Total Acid Number (TAN):  less than 2.0

Wear Metals:    Iron                           less than 300 ppm

                         Lead                         less than 75 ppm

                         Copper                     less than 275 ppm

                         Chromium                less than 30 ppm

                         Aluminum                 less than 40 ppm

                         Tin                            less than 30 ppm

                         Silver                        less than 30 ppm

                          Silicon                      less than 60 ppm

In addition, if the viscosity increases 10% or more between samples and the TAN increases, the oil should be changed.  This is an indication that the oil is oxidizing at a rapid rate. 

Note:  TAN is the amount of KOH required to neutralize one gram of oil and is a measure of the oxidation.  This is sometimes called the neutralization number (NN).  Another measure, the oxidation number, is a product-specific value and is performed on an infrared spectrometer.  The units for oxidation number are absorbance/cm. To use oxidation number, the oil manufacturer must specify the acceptance limits for the specific product.  As an example, Mobil Gear 630 has an upper limit of 8.0.  


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