2021 eco diesel gas mileage

[Ninety-9 SE-L]

Something I recently noticed is that I'm locked out of 7th and 8th gears until the truck warms up. That's the main reason my fuel mileage sucks within the first 5-ish miles.

I was sitting around 48mph on SR580 this morning, and I noticed that I was at about 1600RPM and could not dip below that, even taking my foot off the throttle. After about 2-3 miles, I was able to get down to 1300RPM at the same speed, and before I got to the highway I was finally down to 1050RPM at the same speed.

The final drive ratios for my 3.21:
6 - 3.21, 7 - 2.70, 8 - 2.15

According to my 32.1" diameter tires at at 48mph:
6 - 1,613RPM - (~20-28mpg maintaining 48)
7 - 1,357RPM - (~25-35mpg maintaining 48)
8 - 1,081RPM - (~32-45mpg maintaining 48)
*mpg really dependent on how level the road is.

Since gas prices are up, I noticed more people driving slow. I've been seeing what the truck can feasibly do on my daily commute. I still try to anticipate most lights, light acceleration, early deceleration, keep my foot steady bleeding off speed going up hills and gaining speed while going down. I still drive about 10-15% over the speed limit. I probably can't keep up with this style of driving, but if I'm paying $5.40 at the pump, I may as well experiment.

With this new tank, I seem to be peaking at 28-28.5mpg when I arrive at work or home.

 

[TSL]

I know it's early days yet.... less than 300 miles on the truck....but did my first real trip anywhere in it and was impressed with this result. Drove to the Oregon coast, which from where I live is a 2 lane mountain road with occasional passing lanes. The return trip plus some driving around at the coast which was a mix of highway and in town driving was just under 200 miles and the truck is reporting 26mpg !! No hand calculations here to verify, just what the truck is telling me.
With it being a Rebel, and not even broken in yet, I'm pretty happy with seeing this number.
I wasn't "driving like grandma", but neither was I driving aggressively either. Didn't really pass 60mph very much and generally accelerated smoothly. Trying to be nice to the engine while it breaks in!

 

[flyjets]

I am shocked on how good the mileage is.

Attached 2 photos as proof. This is with the 3.92 rear and totally optioned Longhorn Southfork

 

[StuartV]

So far so good. My first day back to work.

31.2 on the way from New Orleans to Pensacola, on Adaptive cruise control, @ 71mph
29.5 from Pensacola to Tampa on Adaptive cruise control, @ ~75-85mph
20.1 Towing a 16x7 enclosed trailer on the freeway, @ ~65mph
28.2 Mixed Freeway/City in rush hour (note that I had a light foot)

Something I noticed. As much as I like the adaptive cruise control, it's extremely aggressive when I pass someone or traffic speeds back up. The second someone is no longer in front of me, It'll downshift 1 or 2 gears to get back up to speed, and I'll just watch my MPGs plunge. I've found that if I do get behind someone, it's best to cancel my ACC and manually get back up to speed.

In my informal experimentation with Adaptive Cruise versus regular Cruise in my Hemi, I have found that using Adaptive Cruise (on I-95 in moderate traffic) cost me about 1 MPG versus using regular cruise.

It makes sense to me as using Adaptive (when there's any traffic at all) results in the truck slowing down and speeding up a lot more than when I use regular cruise and control especially the slowing down part myself. It feels like the Adaptive actually uses the brakes sometimes, where, if I'm on regular Cruise, I would almost never actually use the brakes. Just hit Cancel to let it coast down in speed.

 

[Ninety-9 SE-L]

In my informal experimentation with Adaptive Cruise versus regular Cruise in my Hemi, I have found that using Adaptive Cruise (on I-95 in moderate traffic) cost me about 1 MPG versus using regular cruise.

It makes sense to me as using Adaptive (when there's any traffic at all) results in the truck slowing down and speeding up a lot more than when I use regular cruise and control especially the slowing down part myself. It feels like the Adaptive actually uses the brakes sometimes, where, if I'm on regular Cruise, I would almost never actually use the brakes. Just hit Cancel to let it coast down in speed.

I agree, I've begun using adaptive cruise more on my commute, but it is both aggressive in braking and accelerating back. I have to be on the buttons a lot. I also noticed that cruise control tends to hang out in 7th, when I'm going fast enough for 8th.

Anyway, just did another fill-up, same as before, mixed driving suburb+local highways. I was doing a bit more in-town driving just before my fill-up, so the fuel economy mileage dipped from the lower 28s to the upper 27s.

According to the dash:
759.3mi driven
65mi remaining (plus about 50mi reserve)
24.5 hours run time (about 3-weeks, June 21 to July 11)
27.7 MPG

According to today's receipt:
I bought 28.837gal @ $5.479/gal....minus 20c/gal from Upside.
$158.00, minus rebate.
759.3mi driven
26.3 MPG

Again, I usually pump to stop, then 2 more stops, then I push it to the next dollar.

 

[Rossum]

10,806 miles driven since new.
Every fill-up recorded.
409.33 (US) gallons used.
= 26.4 mpg average.
Best tank: 28.85
Worst tank: 24.25

This is ~90% interstate highway driving, cruise set to 10 over the posted limit, so 75-80 MPH. Bed usually full under the cover, and most often two passengers.

 

[tom318]

Just wrapped up a trip this past weekend. This is the furthest I’ve pushed mine on a single tank. Best Milage I’ve seen yet since putting on chunky tires. Hand calculated was 28.2mpg and 885mile covered on 1 tank. The range with this 33gal tank is just awesome!

 

[Rossum]

I track every fill-up via Fuelly.
Hand-calculated over the last 9927.7 miles, I've put in 364.177 gallons, for an actual average of 27.26 MPG.
This is 90+% highway driving, typically with the bed full of stuff (but covered) and one or two passengers. Cruise set to 10 over the posted limit, so mostly 80, some 75.

Meanwhile, the EVIC claims 30.4 over the last 9836.7 miles.

That's an ~11% error.

I reset Trip A every time I fill up. I was intending to use Trip B for a true, long-term average, but was dismayed to find that it resets to 0 miles when it hits 10,000. It also appears there's an issue with the hours meter on it. If we divide 9836.7 miles by 39.22 hours we get an average speed of ~251 mph. Nope, sorry, my truck can't go that fast!

I'm thinking the hours roll over at 100? If we divide 9836.7 miles by 139.22 hours, we get an average speed 70.66, which might just be in the ballpark.

 

[RsKeyz]

Others can chime in here if I'm wrong, but my understanding is that neither trip counter calculates past 500 miles. So that 30.4 avg is over your last 500 miles, even though it says 9837.

 

[Rossum]

Others can chime in here if I'm wrong, but my understanding is that neither trip counter calculates past 500 miles. So that 30.4 avg is over your last 500 miles, even though it says 9837.

I would be surprised if that was correct. I have normally Trip A showing all the time. I've never seen any kind of "jump" or discontinuity at 500 miles, and I've gone past 500 miles numerous times (easy when you have a 33 gallon tank).

However, I did hit 20,000 miles today and saw Trip B roll over to zero miles. I've never before reset Trip B, but did so shortly after watching it roll over the mileage, and noting that the time did not roll over with the mileage. Now I'm gonna check when the time rolls over. I'm still guessing it's at 100 hours..? I hate to say it, but it's kinda dumb the way these roll-overs are implemented. If the miles roll over, the time should too (and vice-versa).

 

[RsKeyz]

I would be surprised if that was correct. I have normally Trip A showing all the time. I've never seen any kind of "jump" or discontinuity at 500 miles, and I've gone past 500 miles numerous times (easy when you have a 33 gallon tank).

You wouldn't necessarily see a "jump" if it's a rolling average. The more consistent your driving habits, the less noticeable it would be.
I've also seen someone say it's a rolling average over as little as 200 miles, although 500 makes more sense to me, and here's why...
I've put about 12k miles on my truck, and only reset trip B once. That was after I started seeing these strange inconsistencies on the EVIC and reading more about it.
I do very little freeway driving. My daily commute is mostly hilly and twisty country backroads, with a few miles of in town driving here and there. I average around 23mpg on nearly every tank, hand calculated, and it typically reads within .5 of the EVIC.
A few months ago I jumped out on a road trip with the family, almost all highway. Filled up and reset Trip A before heading out, and smiled as I watched those MPG's hold steady at around 29 on the freeway. I kept switching back and forth between Trip A and Trip B. Not long into the trip, I noticed B was climbing faster than it should have been. By the time we returned home from the 400ish mile round trip, Trip B (which had NEVER been reset in over 8k miles), had jumped from just under 23 mpg, to about 27... In just over 400 miles... It was reading a little bit less than Trip A, it made no sense.
One thing is certain, it was definitely not an average of the last 8k miles. That's the easiest example I have. The closer you monitor both trip computers, the more it makes sense.

 

[StuartV]

I reset Trip A whenever I get an oil change. So, roughly around every 5K miles.

I reset Trip B and the Fuel Economy display every time I fill up.

Trip B and the Fuel Economy display always match exactly - even when I drive 700+ miles on a tank. And, they are almost always showing that I got better mileage than what Fuelly says when I enter my fill-ups. That is true whether I went 700+ miles or if I only went 200 miles.

 

[Rossum]

it made no sense.
One thing is certain, it was definitely not an average of the last 8k miles.

If it really does work that way, it's very misleading. If a "trip display" shows X miles, then average MPGs on that same display should should be calculated over that same distance.