If the bearing is not operating with full film lubrication, it is running in boundary or mixed-film lubrication. At low engine speeds with low viscosity oil and high loads, especially at startup and shutdown, the IMS bearing sees boundary lubrication where there is insufficient kinematic viscosity or bearing speed to create the required elastohydrodynamic (EHD) film to separate rolling bearing elements. Simply flooding the IMS bearing that is already partially submerged with more oil volume won’t prevent increased wear if there is insufficient lubricant viscosity and high loads and can actually cause a bearing to run hot. As bearing speeds increase, the amount of lubricant to support the applied load decreases. This is one reason Porsche redesigned the intermediate shaft starting with the 2006 model year to use a larger diameter ball bearing that in effect increases bearing surface speed, improving the load bearing capability of the IMS bearing at low engine speeds by allowing for full film lubrication at these lower engine speeds.
In fact, the American Bearing Manufacturers Association standard 9 provides a method to calculate effective bearing life with an adjustment factor a3 that when viscosity drops below 13 cSt or when there is very slow rotational speed. In those cases, bearings life can be 20-50% lower. Your IMS bearing regularly operates in these severe conditions where use of a quality oil with an exceptional additive package including moly and ZDDP should be used. Even the slight increase in HTHS viscosity of a 5w40 over that of a 0w40 can provide up to a 10% increase in oil film strength at extreme temperatures a modern engine can see. As an oil ages, viscosity modifiers in the oil break-down allowing for an oils viscosity index to shear out of grade. In the worst case scenario, a new fill of 0w40 with 13.5 cSt viscosity measured at 100 degrees C to shear down to a 30 weight with 10.0 cSt viscosity index at the same 100 degrees C in only a few thousand miles. It doesn’t help matters that these engines run much hotter than 100 degrees C (212F) and can often see temperatures of 240F or higher just sitting in traffic on a hot summer day. With the IMS bearing operating in extreme conditions most of the time with lubricant viscosities less than 13 cSt negatively affect bearing life, selecting the right oil and oil change intervals and deciding when to service your IMS bearing are hotly debated subjects.
Many think that because they are using a synthetic oil that they don’t need to change their oil as often and can observe long drain intervals recommended by auto makers. Although it’s true that modern synthetic lubricants don’t break down, however the additives do. Oils are formulated with corrosion inhibitors, anti-wear additives, anti-oxidants, viscosity modifiers, and other additives that do break down, reducing the lubricating oil’s performance. Besides viscosity loss, contamination from combustion byproducts including fuel and moisture in the engine further degrade the additive package and can reduce IMS bearing life. Lubricant quality and cleanliness is paramount, directly affecting bearing and overall engine health. This is why we recommend
Driven DT40 or
FR50 oils formulated with increased anti-wear and extreme pressure additives for M96 engines and why observing shorter oil change intervals of no more than 6 months or 5,000 miles as part of
regular scheduled maintenance is essential.