According to Alldata, no 2500s in the 06+ have MDS. Since all mega cabs are built on a 2500 chassis, they do not have MDS. Also, that drop in RPM is TCC lockup or overdrive, MDS doesnt cause a drop in RPM, it causes a slight rise by around 100RPM actually since the engine needs to rev a little higher as a 4 cylinder to maintain speed.

Not quite, the oil viscosity problem is actually due to the way the MDS lifters work. They are cycled on and off using oil pressure controlled by a solenoid, They sort of disconect the top half from the bottom when the cylinders are deactivated. Using the wrong viscosity oil causes the oil pressure to be different, and it causes problems with the solenoid and lifters.

 

Correct, The RPM decreases when cruising at highway speeds because of the Over Drive feature on our transmissions, this decreased rolling resistance within the transmission/driveline and reduces RPM and load in order to improve Fuel Economy.

If you turn on tow haul/OD Off then you will see a very large decline in Fuel Economy when on the highway.

BigSloth is also correct as far as the end users have determined. regarding the oil and the solenoids/valves, but without combustion, the 5w-30 (or 10w-30) can still cause cylinder wall issues on the cylinders that are not firing. Dodge basically states that using the wrong oil may cause the engine and MDS system not to function properly, but they haven't officially stated what components are affected in any document that I can find.

So we will just have to take Dodge's word on the matter of Oil.

Not a single Mega Cab Dodge Ram has MDS, if you look at any build sheet of a Mega Cab Ram from 2006+ not a single one has MDS. There are threads that swear they have it on their Mega Cab Ram, but it is usually just misconception of the Over Drive kicking in.

 

Thanks for the info I was taking a stab in the dark at it as i have very little knowledge on how the mds actually works or what it involves but just thru out what sounded logical. Though I am requesting a build sheet to see what my truck came with from the factory since I just got it.

As far as mds i have heard mixed things about it on mega cab from both sources at dodge and random internet databases.

 

well I'm telling you that not a single Mega Cab came off the MFG line with MDS... but your build sheet will confirm it, no worries.

 

I just remembered the OP's original thread about his speedometer not working, and replacing his ABS sensor in the rear diff, then finding the LF hub ABS plug unplugged, and speedo still doesnt work.

I'm not sure of how the MDS decides when to turn on aside from when its at steady throttle, but I would imagine it needs a speed signal from the vehicle to engage. If his speedo is not working, its likely that whatever fault is causing the lack of speed signal is also responsible for the MDS hiatus.

 

I thought he fixed the speedo issue no?

 

You think the LF hub's abs plug will have to do something with the speedo? Why i dont have any on my RF hub?

 

I don't think the front abs has any effect on the speedometer, I just meant whatever does give the signal to the speedometer might also be why the MDS isn't working