Service intervals – Quick Guide
Why are there recommended service intervals for Porsche IMS bearings?
The factory did not originally offer any replacement IMS bearings for the intermediate shaft nor did they offer tools, a procedure to change out the IMS bearing, or even a service interval for the original bearing.
We all know that load capacity is the primary issue with the single row 6204 bearing and that the failure rate is significantly reduced with the dual row bearing by virtue that the dual row has twice the load capacity and that having a grease seal on the original bearing greatly reduced lubrication of the original bearing. That said, we all know that cars that were infrequently driven, poorly maintained, or driven short distances, especially in cold climates, are more likely to suffer an IMS failure.
One reason we mandate service intervals based on time or mileage, whichever comes first, is that contamination of the bearing lubricant (IE your engine oil) by water or moisture as well as by combustion byproducts significantly reduces the bearing life. In fact, as little as 0.002% water will reduce bearing life by 48% and 6% water content reduces bearing life by a whopping 83%* (figures quoted by the McNally Institute). So letting your car sit really is one of the worst things you can do for it, especially your IMS bearing. And regardless of whether you use a ball or roller bearing, contamination in your oil leading to corrosive wear will reduce the service life for any replacement IMS bearing, with exception of the IMS Solution.
The choice of lubricant also has a huge effect on the life of your replacement IMS bearing. A40 oils have reduced levels of ZDDP anti-wear additives and most have only trace amounts of active EP additives such as moly, both of which directly affect bearing wear. The additive package is even more important for your IMS bearing as the typical 0w40 oil will have a viscosity at 100 deg C of 12.9 cSt which is significantly lower than what most bearing manufacturers recommend for lubricant viscosity for a ball or roller bearing of 15 cSt. Those running Driven DT40 should have reduced wear and longer useable life for their replacement IMS bearing than anyone running any Porsche A40 approved oil and use of Driven FR50 or DT50 will provide superior protection given they have a typical viscosity index over 17 cSt @ 100 deg C.