Cummins 6.9L turbo diesel economy

[redpoint5]

Still, 15 MPG at 65 MPH is not great for a diesel. Is this really what these trucks are getting? I don't think I've ever had a tank get less than 16 MPG.

[redpoint5]

Still, 15 MPG at 65 MPH is not great for a diesel. Is this really what these trucks are getting? That's the worst MPG I've ever recorded on my truck, and it has a headache rack sitting above the cab, oversized offroad tires, a loose automatic tranny, and a sloppy front end.

[Hersbird]

Well he said 75mph but the interstate he runs to work on has an 80 mph speed limit and Montana will let you go 5 over all day without a second glance. I bet when it's clear and daylight he is doing at least 75. I also notice I don't see the truck except on the bad weather days pretty much, think cold air, rain or snow, and diesel #2 in the tank. He has a big deer catcher, welded bumper on the front as well after his stock setup caught a deer. I think he feels a little safer with his 120 mile (round trip) commute in the Ram then in his Grand Cherokee, and I don't think he gets much better mpg with the Jeep. He is close to retirement so moved way out in anticipation of only having to do it for a year or so.

[orerockon]

15.7 mpg cruise set at 65 dead flat no wind. Never had it go any higher, and that was before the tires and canopy, driving back from the dealer. 15 maybe 15.1 with the canopy and tires. And yes I do try to not use the brakes and time the lights etc. Heck I even ramped up my no stop at a right turn stop sign campaign. Playing around on a boring trip I did 55 to 70 in 5 mph increments, same stretch, 10 miles each. Highest was between 60 and 65, closer to 65. Starting tanking at 70. So how do you control the regen?

[Hersbird]

From what I read trying to research if I want a 6.7, there are active and passive regens. The truck won't say anything on it's own when it goes into active regen unless the DPF is really full. Basically it only sometimes warns you when you really need to let it finish or risk a 100% full DPF that then won't ever trigger an active regen without a trip to the service center. Other times it just does the active regen when it feels like but unless you have some kind of aftermarket gauge like the Edge, you may not notice. If you stop in the middle, it just restarts next run, again if it doesn't finish, it restarts again. With the EGR and DPF in place I would avoid idle at all costs, that really seems to soot the whole system. The passive regen is just working the truck hard enough that it burns it's own soot, so towing or going up a long hill should give you freebie regens. The DEF system actually helps reduce the number of active regens, so some find better MPG with that system although then you have to buy that crap so they end up paying more.

Personally, I would delete the DPF, deactivate the regen, and turn off the EGR but leave it in place. I would do it even if I were leasing the truck or if it was under warranty, although the trucks I have looked at are all out of warranty anyway, and some have the deletes in place already.

if you want to keep it all stock, an Edge gauge or something similar you could monitor the DPF level and learn when it does active regens. Then next time before it gets that point, a higher speed or a downshift may hurt mpg temporarily, but may get the EGT high enough to get some passive regen going. Then slow back down. If you are going to be adding fuel in a regen, you might as well be using the fuel to go faster ultimately getting better mpg overall.

[gumby79]

Install an EGT (ehxsost gas temperature) gage with a "fast response "prob . Then apply target Egt technique similar todriving with a Vacuum gage except yout target is the lowest temperature to maintain speed instead of the highest Vacuum . For my 1st gen cummins its about 500°f on flats 600 Med grade 700f heavy and 800 for major aka 7%and up ,all at 65-60mph (my trans will not hold OD above 800° below 60mph).
Some times on a grade as the rpm drop the EGT will rise 50-100°f with no change in throttle. in theas situations back off the throttle and maintain your EGT set point . I recommend the "fast response " because with my truck the needle moves at the same speed and ratio as my foot.
Just reducing the pressure but not the position will sometimes result in a 25-50°drop and will cause acceleration. Dont understand the physics behind it ,but it works.
I think the region should show up on the EGT gageas well .

[darknightdiesel]

Hi,

New here but our delivery truck is a 2014 with the 6.7 cummins and highway we get around 22MPG and 17-19mpg city depending on traffic

its been "fixed" of course though

a lot is in the use as well. running your fuel supplement at all times, cleaning the turbo and intercooler each year.

[slowmover]

Best mpg will be at 60-mph or below. The trucks hit a wall at that speed or higher.

For a highway trip under 300-miles, average speed will be close to speedometer set speed if at 60. Faster one goes, the greater the discrepancy between average (actual) and speedo set speed. No lane changes, no braking, no off throttle to deal with traffic, etc.

This is so up to 62-mph. After that one is mixing with commercial traffic

High mpg is long term discipline. Several hundred thousand miles. The diesel fuel advantage takes just about 200k miles to achieve (over gasser equivalent) in a pickup.

15 is what I average with a 35' travel trailer. It's lousy for a solo truck.

And the engine is a 6.7. Only 6.9 was a 1980s Ford with a Cornbinder oil burner.

[Fingie]

Originally Posted by orerockon

And for the record my truck is 100% stock and the tires are actually an inch smaller because I need an aggressive tread and the factory size tires are $400 more for a set

I wonder if this is the reason for your current mpg?

[orerockon]

Originally Posted by redpoint5

Still, 15 MPG at 65 MPH is not great for a diesel. Is this really what these trucks are getting? I don't think I've ever had a tank get less than 16 MPG.

14 MPG seems to be a "real world" consensus for the 6.7L diesel 2500 (not just highway). It's pretty easy to keep 14 with no load and significant highway miles. 17 highway (EPA says I think). Remember this is on a 2012, they're getting better every model year (16 on the 2016). I've never got that high even on short stretches under ideal conditions. Maybe at 100 degrees with a tailwind lol. BTW I've cruised the net and Cummins 67.L should be run at 1500-1600 RPM for best economy. Now if I could only keep that through acceleration up to cruising speed lol.