Surprising finding - comparing the MPG of my RAMs

[geotex1]

So, for the past two months I have had the opportunity to run both of my RAMs over the exact same routes, multiple tanks of fuel, various climatic conditions, and computed MPG by hand as also recorded what the trucks were suggesting to be the mileage.

The comparison is my 2019 RAM 1500DT 5.7L Hemi Laramie Crew/Long/4x4/3.92 gearing versus my 2015 RAM 3500DS 6.7L Cummins/AISIN Longhorn Crew/Long/Dually/4x4/4.10 gearing.

I had this opportunity as a result of having storm damage repairs done to both so they were in and out of the shops at different times. Normally, the 3500 is relegated to heavy hauling duty only.

Comparisons were done with round trips, and I threw out trips from the comparisons where idle time was greater than 10% different due to traffic/road construction/accidents:

1. To/from my office which is 84% country road @ 40mph or less and 16% highway @ 55-65mph - total 84.6 miles and 5 comparative trips for each truck;
2. To/from the airport, which is 21% country road @ 45mph or less and 79% interstate @ 70-75mph - total of 204.1 miles and 2 comparative trips for each truck; and,
3. To/from family vacation rental, which is 15% country road @ 40mph or less, 63% highway at 55-65mph, and 22% interstate @ 70-75mph - total 350.8 miles and 2 trips for each truck.

Had very similar climatic conditions ranging from clear days with ambient temperature in the mid-70s with 50-68% humidity to ambient temperature 95-98 degrees with 88-95% humidity, and for #1 and #3 rainy days with temperature at 68-72 degrees and at 89-91 degrees. I made a conscious effort to leave stops with equal acceleration since the Hemi will take the Cummins off-the-line every day, so I eased to speed. I am also a ridiculous creature of habit and the HVAC is always at 69deg. I did not control the variable of how full the fuel tank was each trip, but both had empty, open beds and just me as the driver and with the same computer messenger bag and rollerboard luggage. The 2015 is well broken in and had an oil change, both fuel filters changed, and a filter and fluid service for the AISIN at the start of this, and the 2019 had a fresh oil change. BIG difference in tires between the two as my 5th Gen is wearing factory Bridgestone all-seasons 20s, and my 3500 wears 17" Nitto EXO Grappler LR Es at all positions. The diesel also wears all of it's factory emissions because I have a Mopar MaxCare extended warranty, and normally it has a Pedal Commander to offset the known lag of my engine/trans combo, but the PC crapped out on me a few months ago. The 2019 powertrain is also stock.

Here's a summary of the overall averages for each of the above:

1. Both of my trucks yielded comparable fuel efficiency - 5th Gen is 15.8mpg and 4th Gen is 15.6mpg.
2. 5th Gen lead with 17.6 versus 16.0mpg.
3. 5th Gen blew it out with 18.1mpg versus 16.4 (diesel's sweet spot is 62-65mph, so better than #2 was anticipated).

To be honest, I have been critical of the fuel efficiency of my 5th Gen because my 4th Gen 1500 Sport was always more efficient, but fuel efficiency isn't a deal breaker for me. However, I was very curious to compare my two trucks more rigidly because I had noticed that my general, around town mileage was incredibly similar between them, and, of course, the 3500 is twice as heavy as the 1500 and takes a lot more to get moving, especially with 2 more all-terrain tires and sitting much higher than the 5th Gen.

Regardless of the efficiency, the diesel is always more expensive to run, especially here in PA where the cost of diesel is generally $0.50/gal higher than unleaded.

 

[Rick J]

Interesting comparison. One thing I noticed, your calculator needs to be fixed. All three of your scenarios add up to 109 or 110% I've never owned a diesel but I thought they were supposed to get much better mileage than gas so that may account for why the heavier rig got close to the same as the 1500.

 

[geotex1]

Interesting comparison. One thing I noticed, your calculator needs to be fixed. All three of your scenarios add up to 109 or 110% I've never owned a diesel but I thought they were supposed to get much better mileage than gas so that may account for why the heavier rig got close to the same as the 1500.

Lol! Fat fingers and a tiny smartphone keyboard! Let me proofread and adjust. Only scenarios 1 and 2 were mistyped.