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Not getting the MPG I think I should

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So, my normal commute is 37 miles one way, with about a 2000 ft elevation gain on a 2 lane road. I've had worse commutes... That being said, I've been averaging about 33 MPG per tank. Ok, I understand with the mountain, that's not bad. But over the weekend, I took interstate from home to Black Mountain, NC. I-77 to I-40. Even with cruise control set most of the way at PSL (70, then 65) I only got 37 MPG average. On the way home, the trip started down a big mountain, so I was able to average 42. Not as good as I was expecting.
What items should I be looking at on my 2014 CTD?
I've already:
Changed all filters except the fuel filter. (Dealer changed that right before delivery, there is still 47% life on it.)
Put in amsoil oil and transmission fluid. (Flushed transmission)
Cleaned the MAF.
Tightened the 5 hose clamps from the air filter onwards.

I was thinking maybe have the dealer:
Reset the LTFT
Flash the HVAC (I have the humming noise when the car shuts off, and if I maintain 70 or greater with RPMs 2K or over, the A/C shuts down - but that's another story.)

Any other things I should consider?
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Discussion Starter · #5 ·
Cold tire pressure was 42, checked while driving, 44-45. (Aired up that morning)
I was under the impression that you clean the MAF when you change the air filter. I suspect it couldn't hurt, and who knows if it had ever been done. Either way, now it's clean.
2K is running about 70-75 on the highway. (probably closer to 75.)
 

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Discussion Starter · #8 ·
Traveling at those speeds is one of your problems.

Best mpg on this powertrain has consistently been achieved by cruise control anywhere between 60-65 mph.
Ok, I understand that 70 (which is PSL on I-77 and parts of I-40) isn't the best. But when I was coming home, I kept cruise set at 65 on the majority of I-40, and I was barely getting 42. And that's with starting out down a big mountain. I'm not convinced that it shouldn't be better. Yes / No? (I'd really like to see 45 or possibly above.)
 

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Discussion Starter · #10 ·
it really seemed to be happier (fuel-wise) at 70-75 mph than at 55 or 60 mph.
...and that's what I'm looking for. I'd like to see some improvement in my MPG - I know the car can do it, I suspect there is something that isn't quite right and I don't know where to start checking.
 

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Discussion Starter · #13 ·
Don't worry, I don't care for seafoam. And I do know better to use it in a diesel.

Get your brakes checked - something's dragging. At 70 MPH you should be running in the high 40s for MPG. Also, when descending put your car into metric and make sure the instant fuel consumption readout drops to 0.0 L/100 KM. This will verify your car is going into DFCO properly.
I'll do those, thanks. Since I go down the mountain on the way home, checking the DFCO will be easy.
 

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Discussion Starter · #15 ·
Yes your MPG is definitely low. I second the notion of checking the brakes for dragging. Also, do you still have LRR tires?
I think the tires are original, I'll have to look. They have 5/32 left on them last I checked. Almost due for new ones, I am contemplating Continental Pure Contacts.
 

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Discussion Starter · #18 ·
While I love this tire, they're NOT a MPG tire. They excel at being fantastically grippy with good road manners in all conditions, but I think I lost mileage even over my FR710.
Hmmm. Interesting. Their website states it is an Eco tire. I'm not sure if that translates to LRR or not. But, if the MPG loss isn't too bad (1-2) then that might be ok if I get everything else to cooperate and get the MPG where I want it. I do have this mountain to traverse each day, so the grippy part may outweigh the need for the extra 1-2 mpg. If the weather gets too bad, then I'd want to take the Suburban. Talk about a loss of MPG! I'd rather take the Cruze as often as possible.
 

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Discussion Starter · #27 ·
Is is it possible the op is regen in really short intervals?
Don't think so - I have the Scangauge II (Great! Just love it! This is something all CTD owners should have.) and usually there is about 200 or more miles between regens.
 

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Discussion Starter · #35 ·
Also, when descending put your car into metric and make sure the instant fuel consumption readout drops to 0.0 L/100 KM. This will verify your car is going into DFCO properly.
Did this on the way home yesterday - worked as expected. (And going down the mountain raised my average for this tank to 34.)
 
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Discussion Starter · #39 ·
OK - next test. On a relatively flat stretch of highway (rolling hills are ok as long as up and down are roughly equal) reset one of your trip odometers and watch the average MPG vs. average speed. Report distance, speed, and mpg numbers in both directions on this stretch of road please. What I'm looking for here is to see if your car is performing properly on the highway.
Ok... Shall I set cruise control? I think there is a (mostly) flatish stretch on the way to Winston-Salem. I should be able to do this Sunday.
 

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Discussion Starter · #48 ·
Do you take the fuel usage off the DIC, or at the pump when you fill it? Cruise set at 110kph has my RPM at 1750. The Australian diesel has the 6T45 automatic and a 2.64 diff ratio.
I've been using ACar on my phone, that does the calculations from mileage / gallons and I keep an eye on the DIC to get a general estimate as to how I am doing. The ACar app is what I am ultimately going by for the MPG per tank.
 

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Discussion Starter · #64 ·
OK - next test. On a relatively flat stretch of highway (rolling hills are ok as long as up and down are roughly equal) reset one of your trip odometers and watch the average MPG vs. average speed. Report distance, speed, and mpg numbers in both directions on this stretch of road please. What I'm looking for here is to see if your car is performing properly on the highway.
Sorry for the delay, but life sometimes gets in the way... here are the test results.
Test course – US 421 between Windy Gap and Yadkinville NC
Sunday, 10/2/16; 1:45 – 2:15 PM @81 degrees (A/C on for all tests)
Tire pressures: RF 42; LF 41; RR 42; LR 43

Cruise control set to 55 mph
RPM average 1500 – 1600
52.5 mpg @ 6 mi – 55.1 average speed

Cruise control set to 65 mph
RPM average 1800
46.0 mpg @ 5.4 miles - 65.4 average speed

Cruise control set to 70 mph
RPM average 2000
35.3 mpg @ 10.6 miles - 69.5 average speed
34.5 mpg @ 12 miles - 69.7 average speed (continued from above test)

No cruise control
42.3 mpg @ 6 miles - 68.9 average speed
40.9 mpg @ 7.2 miles - 66.1 average speed (continued from above test, includes going from US 421 to I-77)
36.5 mpg @ 6.3 miles - 73.2 average speed (Test on I-77 N)

Since the test, I've had a flat, (wore out the inside edge of the tire, but the alignment #s didn't show anything really out of whack... very strange.) got all new tires (Continental Pure Contacts), front end alignment, had the HVAC flashed to fix the hum issue and had the LTFT reset. We'll see if there is a difference. I also ran a tank of B18 through it before I got the flat as I wanted the detergent properties of the bio to make sure everything was "cleaned out" so to speak. Now I'm back on regular diesel from Sheetz. We'll see what happens...
 

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Discussion Starter · #65 ·
So after all of the above, I seem to be a bit happier at roughly 35 MPG per tank (using ACar app to record mileage / gallons for calculations) and that's with my 37 mile drive to work with the 2000 ft elevation change. Not bad. I'll be going from NC to CT after thanksgiving, we'll see what happens. I am looking forward to seeing what kind of mileage I get on that trip as I don't get to do a lot of highway driving. (My work ride is 45-55 MPH roads, so not terrible, but it's still no highway.)
I also just had the NOX sensor recall done, we'll have to see if that affects anything.
 

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Discussion Starter · #67 ·
I would think that most of what you lose going up the 2000 ft change, you would gain back coming back down.
I guess that depends on how hard I pass whatever log truck or tractor I encounter on the way up... :wavetowel2:
 
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