I am new to this thread & would like to know what the difference in MPG is for the two stock engines given everything else is equal. I am in the market for a dodge diesel probably 2006/07/08 quad, 4x4, long box so am interested in MPG. Also once the warranty is over with whick engine costs the least to improve mileage? I appreciate your input.
Terry

 

Stock for stock, the 5.9 gets much better fuel mileage.

The 6.7 has the 4th injection event, EGR and DPF to deal with and this kills the mileage. The regen cycles are what really kills it.

With a stock 5.9, you can expect 15 - 18 on a daily basis, depending on gear ratio, transmission and driving style.

With a 6.7, you can expect 12 - 15 under the same conditions.

 

I have a 2007, 2500 SLT, Mega Cab with a 6.7 CTD, 4X4, six speed auto. The best milage that I have had was 17 mpg. The average to and from work is 12 - 14 mpg. When I tow my 30 ft fithwheel I get @ 13 mpg.

 

If you get a 5.9L add a chip you should get 18 or 19 with 3:73 at 60 mpr auto 48RE .
the 5.9l has a 3th injection event as well to clean up smoke

 

Just as an example of what the right tuning can do, mine as it sits right now, get's 16 - 18 during day to day driving and 20 - 21.5 on the highway if I keep the boost in the single digits and the EGT's below 700.

Start going higher than that and you're burning more fuel.

I find that driving by the EGT, boost and engine load % numbers is where I get the best mileage, not so much speed or RPM numbers.

 

how do you monitor that(EGTs)?

 

You need an EGT gauge.

For monitoring performance, you want it mounted pre-turbo.

For using for cool down or monitoring an exhaust brake, you want it post-turbo.