I posted this question when I got my 2009 R/T on this forum. No one has been able to answer this question.

The owners manual (page 110) talks about the "fuel savings" message coming on (above the average MPG line in the information screen) whenever the engine goes into the MDS mode.

I have NEVER seen this "fuel savings" message come on regardless of how steady I drive the car at a constant speed.

I have not been able to determine when the engine is switching off 4 cylinders. It is a very smooth transition that I can not detect.

All I know, is thus far when I drive my car in a passive manner, the engine returns about 18 MPG. I am guessing that the MDS is kicking in and therefore the mileage is decent.

When I drive agressively (who can resist?) the engine returns only 13 MPG.

I have not taken a long highway trip with a steady 70-75 MPH speed; but I hope that it gives me at least 20 MPG.

I have asked the dealer and the zone technical office why the "fuel savings" message does not come on. Thus far, no one can explain this.