Originally Posted by 5500
Not sure how MDS affects transmission operation.
Typically its cold oil viscosity thats critical to engine controls like variable valve timing and mutiple cylinder control, etc... These types of controls are managed with oil pressure and in order to have adequate pressure at colder operating temps the oil has to be thin enough to flow. Once the oil reaches operating temp, it usually thins out enough that flow isn't an issue. Thats why many manufacturers require a cold viscosity of 0 or 5. I think the hot viscosity of 20 is to hel achieve mileage figures.
I personally don't like the driveability when MDS is active, but I like the ability to defeat it. Still haven't decided if it actually saves me any fuel.
No, I don't think MDS has any direct effect on the transmission or shifting. I just think many are attributing "some" driveability issues to the tranny when in fact it's probably the MDS...especially in town. I believe the often mentioned "shudder" or rough shifting is sometimes the MDS kicking in and out and especially more noticeable in slower city driving. MDS can feel a bit like the tranny shifting in and out of a couple of gears at slower speeds IMO. A quick check of your tach will usually show that's not the case. And I'm not talking about torque converter issues and such that are more common in the case of some/many of the 2011 models. While I have no complaints about the shifting and operation of the MDS on my '12 Express, I think some are hypersensitive to the operation of MDS and the shifting characteristics of a truck. I think many who expect luxury car smoothness out of a tranny made to tow thousands of pounds might be somewhat disappointed with most truck trannies. Shifting pressures and stronger components necessary to take towing abuse almost always have a lack of silky smoothness "compared" to a sedan tranny. In fact those of us who have owned numerous trucks over many years have seen the result of manufacturers trying to deliver car-like smoothness and efficiency in their truck trannies. Towing often suffered and failures increased.