Sorry but i call BS on the 5w30 I dont believe the engine can tell if you are running 5w30 10w30 5w20 etc etc etc the difference at running temp between a 5w30 vrs 5w20 is so small the engine has no way of detecting that !! sorry I need more facts before you can sell me that theory !! That is like saying if you let air out of your tires it will cause more drag on the engine and the MDS wont work .

 

I read this thread just hours after putting a bunch of money on an 08 QC 5.7L.... Scared the heck out of me! I traded my 03 4.7L in on the new truck a couple of days ago. After about 200 miles (its fun to drive) I am averaging 17 MPG. This is up from a regular avg of 13.4 MPG. I'd say the MDS is great!

As far as your anti freeze goes, there is no doubt in my mind its the head gasket. This is not an uncommon problem, had a HG problem on a 00 Durango, same symptoms..... I agree with some of the other posts, if you are not getting the answers you want from your local dealer, go to another one.

 

Well, your right MDS doesnt hurt the tranny. Personally i just feel it shifts alot to find the right gear and use mds. In this cold weather, on my short drive to work and around town. I like to trn the OD off. I feel it shifts less. therefore is a little easier on the tranny.

i realise this is what they are made for, blah blah, but it makes me feel better

 

Well, I hav a flowmaster exhaust, and can clearly hear when MDS kicks in. They put 5-30 in my truck on the last oil change without telling me, but I can still hear the MDS kick in and out just as much as with the 5-20 oil...

 

I don't blame you. Maybe this will help.

Here's the TSB: http://wkjeeps.com/tsb/tsb_wk_0901504.pdf
"Vehicles with the Multiple Displacement System (MDS)must use SAE 5W-20 oil. Failure to do so may result in improper operation of the Multiple Displacement system (MDS)."

More information on MDS is embedded in this write-up: http://www.allpar.com/mopar/new-mopar-hemi.html
An excerpt: "The system deactivates the valve lifters. This keeps the valves in four cylinders closed, and there is no combustion. In addition to stopping combustion, energy is not lost by pumping air through these cylinders."

In the write-up there are pictures of a Hemi cutaway illustrating how the oil flows todeactivate the valve lifters.Nothing I read anywhere explicitly says this, but my guess (and this really is a wild-assed guess) is that some amount of testing revealed that using a higher viscosity oil has an adverse effect in the ability for the system to deactivate the lifters properly; maybethe system doesn't work at all under any conditions(which seems to have been disproven empirically by bwhite757), or perhaps it just doesn't work as well... the transition between 4cyl and 8cyl operation is said in the write-up to take 40 milliseconds, I'd imagine that a higher viscosity oil may increase thattransition time somewhat.

I think the MDS is great. I get much better gas mileage in my '07 on my 40-mile commute when compared to an '05QCHemi(pre-MDS) I rented acouple of years ago.

 

good info in thebean's posted links above

Kudos to him for sharing that.

 

well eat my shoes !! that made for some good reading !! thanks for the post .

 

It's interesting to read how different stock trucks work differently. I too have an 06 Nightrunner with the Hemi MDS and Tow/Haul disables the MDS and I get all five gears. There have been posts that Tow/Haul losesan O/D gear. I get all gears in Tow/Haul with no MDS. Tow/Haul changes the shift points and it does take longer to get into 5th, but I have the same eventual cruising rpms at 65mph in Tow/Haul as I do without it. I have read on other forums that the Diablo tunerhas an option to disable MDS and Edge is supposedly coming out with a tuner soon, not sure if theirs has that option. Superchips, while they do not currently have the MDS disable option, appears to respond well to input from it's users and is constantly updating their 3815 tuner for the 04-07 Hemi. I personally like the MDS. I have a wife and 2 young boys (that require alot of crap to go anywhere for any period of time) and we go on 3-4 road trips down south(with the truck to carry all their crap)and it is nice having the MDS. Around town driving I get between 12-15 and highway around 20 +/-. Maybe there is an updated re-flash of the computer that you could ask your dealer about. I know when I went in for my first oil change at 3kmi, they re-flashed my truck with updated programming. I didn't know about it until I read it on the service order???

 

there is a flash available to disable MDS

 

that is weird. I have an 06 SLT. I lose an O/D gear but keep mds in tow/haul. O/D off drops both overdrives and stops MDS...

i like the mds also by the wya