We Put Our 2020 Ram 1500 EcoDiesel Through Our Highway MPG Test:

Comparing the 3.92 Gears To The 3.21s On The Highway

Last month we ran a 2020 Ram 1500 EcoDiesel with the 3.21 gears on our 172 Kilometer (106 Mile) highway MPG loop and got a very impressive 7.8 l/100km or 30.3 miles per gallon. I spent a week with that truck and was so impressed with it that the day after I returned it to the press fleet I purchased our new long-term 2020 Ram 1500 Laramie Longhorn EcoDiesel. 

Mechanically there are two differences between our Longhorn and the Limited that we did the MPG loop with last month. The Limited, of course, had the air suspension which lowers itself into aero mode on the highway, while our Longhorn has the standard steel suspension at a fixed ride height. The other difference is the Limited that we tested had the 3.21 gears while our new truck has the 3.92s. 

5thGenRams Highway MPG Loop (Google Maps)

I knew that this would make for an interesting comparison so I set off to run the same highway loop we have used to a few times now so we set off to run the same loop during similar weather conditions. The way we run the loop is always the same, we use the same gas station, same pump for initial and after run fueling using the 2-click method, set the cruise control at 113 km/h (70 MPH) and let the vehicle do the work. We don’t use any hypermiling techniques and just drive as an average person would.

Due to less traffic on the roads, we completed the loop 3 minutes faster than we did with the last EcoDiesel giving us a moving average speed of 105 KM/H (66 MPH) compared to 102.6 KM/H (64.1 MPH) in the last truck. At the end of the test, the cluster was showing 8.8 l/100KM (26.6 MPG), after hand calculating the results we came away at 9.05 l/100km (26 MPG). 

The truck with the 3.21s on this test put down a hand calculated 7.8l/100KM (30.3 MPG) so you can see there is definitely quite a bit of difference there. I don’t think that the gearing and difference between air suspension and not alone is worth 4.3 MPG over this test and think there could be a few other factors at play. The Limited that we tested did have some more miles on it (not by a lot though) and with that actually being the first highway trip that I took our new Longhorn on it is possible it might have done a regen during that trip. 

I plan to re-run the trip on our truck in the coming months hoping for a better result, but right now it does give us an interesting comparison point.

Jared Balfour

Jared founded MoparInsiders and is a 41-year-old automotive enthusiast from Vancouver, British Columbia. He took an interest in cars at a very young age and has been interested in them ever since. His hobbies include photography, videography, drag racing, and auto detailing. He currently owns and drives a 2023 Audi RS6, a 2024 GMC Sierra, and a 2015 Dodge Challenger Hellcat.

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