Thanks for sharing the link to the report, two.fiveM35, good stuff. The Amsoil looks really good. Going to their website, they have a lot of interesting information. In the Technical Service Bulletin on Thermal Runaway, it describes the phenomenon this way: "The extreme pressures and temperatures generated by modern vehicles increase stress on gear lubricants and can lead to a serious condition known as Thermal Runaway. As temperatures in the differential climb upward, gear lubricants lose viscosity and load carrying capacity. When extreme loads break the lubricant film, metal-to-metal contact occurs, increasing friction and heat. This increased friction and heat, in turn results in further viscosity loss, which further increases friction and heat. As heat continues to spiral upward, viscosity continues to spiral downward. Thermal Runaway is a vicious cycle that leads to irreparable equipment damage from extreme wear, and ultimately catastrophic gear and bearing failure." This bulletin also says "Viscosity is the most important property of a lubricant in its defense against friction and wear. Viscosity correlates to film thickness and film strength, which keep moving parts from contacting each other and creating increased friction, heat and wear. The higher the viscosity of a lubricant, the greater protection it provides. Note, however, that too thick a lubricant is detrimental because it consumes more energy."
The transfer case in my M925 gets noticeably louder when fully hot, with lots of gear whine sound, and the fluid seems really thin when checked hot. Does anybody have any experience running a heavier weight such as 90W-140 in a M939 transfer case?
