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Just another old guy...
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45 Posts
Discussion Starter #1
I don't know if this is odd or not; it is to me, but since I'm new to diesels, maybe it's pretty simple, and I just don't know it.

Recently bought a 2006 Lariat, 2X4, had about 115k miles, studded, Air Raid filter, EGR delete, and 4" exhaust. For the first tank of diesel, I was getting just a shade under 16 MPG, which I thought was a little low, but okay. After that first tank, I changed both fuel filters (Motorcraft replacements), and both the oil filter (Motorcraft again) and oil (Rotella T6), and started to use Arch Oil AR6200. The second tank saw mileage drop to 15, the third dropped to 14.2, and the most recent was all the way down to 13.5 MPG. I don't have a scanner yet, but there's no unusual readings on the standard gauges; everything seems to be within normal, or at least expected, ranges. There isn't any real hesitation, sluggishness, smoke, or what sounds or feels like a skip; honestly, I don't even know where to start, I've never had this issue with my trucks before (although they were all gassers).

Any suggestions as to what to look for, or check...?
 

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Are you caculating mpg off of the dash or are you doing it manually?
It could be you're getting used to the truck and are driving it harder ?

Sent from my VS985 4G using Tapatalk
 

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Just another old guy...
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45 Posts
Discussion Starter #3
Are you caculating mpg off of the dash or are you doing it manually?
It could be you're getting used to the truck and are driving it harder ?

Sent from my VS985 4G using Tapatalk
I do it manually; I've never found the dash reading to be all that accurate. I'm weird enough to do it with every vehicle, every fill-up... lol

I should have added that most of the miles have been highway miles, 75 mph, A/C on. The second tank was more small town driving than the others; not city stop and go, but not just cruising, either.
 

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EA - Eggfarts Anonymous!
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18,844 Posts
i have an 06 2wd, and i get down to 13mpg all city miles with winter fuel driving relatively hard & letting it warn up a lot, and all the way up to 20 mpg all highway driving at 2000 rpm summer time. these are 'truck unloaded' mileage values.
 

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Just another old guy...
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45 Posts
Discussion Starter #5
i have an 06 2wd, and i get down to 13mpg all city miles with winter fuel driving relatively hard & letting it warn up a lot, and all the way up to 20 mpg all highway driving at 2000 rpm summer time. these are 'truck unloaded' mileage values.
Mine was unloaded as well, with a bed cover; just seemed odd to be steadily dropping like that. I'm going to continue with the Arch Oil, but I'm obviously not sold on it right now. We'll see what happens when I change the oil again...
 

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I saw zero difference with the 6200 so I stopped using it as well. My mileage dropped just like you're saying, but only because they switched over to winter fuel. lol If you're absolutely certain your driving pattern is 100% the same, then you may want to look into a scanner to see what's going on with the engine. Having said that, to really be sure, set up an identical road test. For instance, fill up then hop on the interstate and drive with cruise control on for a set distance, such as 30 miles, and then back to the same gas station. Fill up. Calculate mileage. Now repeat. The reason I say do two round trips is to account for wind and traffic conditions. You might have a tailwind one direction but a headwind in the other. You can also do the same for some city driving.

After doing this, you may find your dropping mileage is due to your driving habits and not the truck....or it may even be the truck! lol
 

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Just another old guy...
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45 Posts
Discussion Starter #8
I'm not dropping the 6200 yet, because I'm not sure that that is what is causing the issue, but it is kinda 'guilty by association' at this point. I won't say that my driving has been quite the same for every tank, but it's been similar; mostly highway miles, where I set the cruise control to 75 on long stretches (of which there are plenty; this IS Texas!). I see some variation on my other vehicles, but not generally to the same extent, percentage-wise. My other truck ('85 GMC SB, FI 350 w/OD) is the only one that will drop like that, but that's pretty much just driving in town.

My first big purchase will (soon) be an Edge or CTS, so that I can get a better idea of what's happening in the engine, but until then, I'm left just kinda wondering...
 

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Just another old guy...
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45 Posts
Discussion Starter #9
im the nut that pulls into the same station on teh same pump pointed the same direction each time if i can lol! and seriously, the winter fuel seems like it steals 2mpg sometimes !!! is it just me?
Now that's making sure you get the same base to compare...! lol
 

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My first big purchase will (soon) be an Edge or CTS, so that I can get a better idea of what's happening in the engine, but until then, I'm left just kinda wondering...
For now, save some money and get the TorquePro app for Android along with the bluetooth OBD-II adapter. I only needed an EGT and fuel pressure gauge to round out what I could monitor using that. This isn't saying it's better than the Edge or CTS, but I am saying it will do what you need until you save up for the fancy stuff.
 

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Just another old guy...
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45 Posts
Discussion Starter #11
For now, save some money and get the TorquePro app for Android along with the bluetooth OBD-II adapter. I only needed an EGT and fuel pressure gauge to round out what I could monitor using that. This isn't saying it's better than the Edge or CTS, but I am saying it will do what you need until you save up for the fancy stuff.
Looked into this, but for Apple, since I don't have an Android phone; that option doesn't look as good. I've looked at some stuff that just monitors for a pretty decent price, but since I plan on adding a few tunes down the road, I figure I might as well just do a single larger purchase, instead of multiple smaller ones. Although, if the reviews on the Apple app for this were better, I might have considered it, just to have right now...
 
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