I have been looking at newer trucks ( 2014-2016 ) and seeing the MDS after the enging size . What does the MDS stand for & what does it do ? Would it be wise to just buy a truck without this ? I tow a 26' enclosed car hauler & want to stay with gas . Gary

Multi displacement system. It shuts off 4 cylinders at cruising speed to save fuel.

2009-2014 5.7 V8s have a recall out just recently where an all plastic shoe in the timing chain tensioner mechanism cracks in two and is causing the chain to break after many hours in MDS mode. Severe engine damage occurs. Hemi V8 s in front of manual transmissions are not having the plastic shoe crack, at least yet.

So will all engines have this MDS ? Can it be turned off ( switch ) Thanks Gary

It varies by year and model.
Aftermarket chips are sold for some year models.
Some models have transmission settings that lock out tow haul.

It will take dealerships so long to fix the plastic shoe on the timing chain on this many affected engines that i would not be surprised if FCA issues a TSB that locks out MSD until the repair can be started.

My memory is fuzzy but i believe that if you wire in a resistor into the Engine Coolant Temperature Sensor thermistor to fool the PCM computer into thinking that temperature is less than 183 degrees, MDS will not engage because "warm up" has not completed. This will set a check engine light.

Hey , thanks for the info , hopefully they will get a handle on this issue . I do hope it is not activated while in tow mode . Gary

Or you could simply unplug the harness that sends the signal to the solenoids to switch into 4cyl mode. It runs into the lifter valley on the driver's side rear of the engine, I believe it is a 6 wire plug.

Can buy a diablo sport tuner and shut it off also.