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Old 01-10-2011, 02:39 PM   #1
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2011 Ford Super Duty Diesel, Don't trust the fuel calculator

Don't get my wrong, I love my new 2011 F250 4WD 6.7 diesel Lariat Super Cab Longbed. Way better than my 2001 F350 7.3, which was a great truck. So the story goes like this:

Using the built in miles to empty calculator, I filled the tank when it said it had 10 miles left. However, it only took 33.72 gallons meaning it should have had about 5 gallons left. That seemed pretty conservative to me. I mean why have a 38.5 gallon tank when you can only use 34.

So the next tank, I decided to push it a little more and went 20 miles beyond when the miles to empty calculator said I had 0 miles left before I ran out of fuel. I had reset the trip computer when I last filled and the trip computer said I had only used 34.4 gallons. So it appeared I still had about 4 gallons left. Fortunately, I was prepared with a 5 gallon carry can. About 5 miles before total empty, I noticed it cranked a little longer before it would start. Just before it ran out, a warning came on the screen stating that power was being reduced. If this happens to you, you only have several hundred feet to pull to a safe location.

Bottom line, when I filled with the 5 gallon can and then went immediately a couple miles to fill, it took a total of 37.87 gallons including the 5 gallons. So between the mileage left calculator and the gallons used calculator, I'm not sure which to trust. For now, I'm going by the mileage left calculator until I get more experience with both.

Another thing, if I ran out of fuel with my old 2001 7.3, it would not take too long to purge the air out of the system. On the 6.7, it took much longer. The manual says to turn on the ignition switch for 30 seconds and repeat 6 times. This is standard procedure when purging air after changing the fuel filters. In this case, I had to do it about 15 times. I was just getting to call for a tow, when it finally fired up.

Some might think me a little nuts, but I really would like to know what kind of margin I have if I'm in a difficult situation. So far, I'm still not sure and will continue to monitor. Love to hear some of your experiences. I see a lot of threads on adding an extra bed mounted fuel tank, but that is not an option for me.
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Old 01-10-2011, 05:06 PM   #2
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I once had a Dodge ,that when the fuel light came on you had about 1/2 mile to go. I found out the hard way. Dave
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Old 01-10-2011, 05:16 PM   #3
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The 2011 Super Duty order guide says you have a 37.5 gallon tank. My plan is to just fill up as soon as possible when the light comes on.
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Old 01-10-2011, 06:44 PM   #4
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Quote:
Originally Posted by hhendrix View Post
Love to hear some of your experiences. I see a lot of threads on adding an extra bed mounted fuel tank, but that is not an option for me.
Closest I've gotten to "empty" was just recently. The dash said "14 miles to empty". When I filled up it took 29.5 gallons, 5.5 gallons less than the stated tank capacity of 35 gallons (gas model).

I guess I may have to run it to empty to find out for sure.

Transfer Flow has a 50 gallon replacement tank for the 2011 Superduty that will work with crew cab 6 1/2 ft beds.

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Old 01-10-2011, 06:51 PM   #5
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Titan Tanks has a 65 gallon replacement tank for long beds.

Ford Large Capacity Diesel Fuel Tanks for Pickup Trucks ~ TITAN Diesel Fuel Tanks: The Leader in Aftermarket Fuel Tanks
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Old 01-10-2011, 07:03 PM   #6
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Wow 65 gallons of fuel. People cringe when they have to haul 30 gallons of fresh water. They worry what effect it will have on mileage.
What is the reason for the huge tanks?
Fill up when it is cheap, drive longer distances between fill ups, worried about finding fuel?
Not criticizing just wondering.
Hickory
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Old 01-10-2011, 07:19 PM   #7
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What is the reason for the huge tanks?
Fill up when it is cheap, drive longer distances between fill ups, worried about finding fuel?
Hickory
Yes.

If you're already hauling heavy and don't need the distance, you don't have to fill'er all the way up...
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Old 01-10-2011, 07:35 PM   #8
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Transfer Flow has a 50 gallon replacement tank for the 2011 Superduty that will work with crew cab 6 1/2 ft beds.
Yep - that's a perfect amount of fuel for me and is on my short list but maybe this fall - gotta get my tonneau cover (or cap) and bed rug first...

Oh yea, and the truck...
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Old 01-11-2011, 05:05 AM   #9
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Originally Posted by hickory View Post
Wow 65 gallons of fuel. People cringe when they have to haul 30 gallons of fresh water. They worry what effect it will have on mileage.
What is the reason for the huge tanks?
Fill up when it is cheap, drive longer distances between fill ups, worried about finding fuel?
Not criticizing just wondering.
Hickory

All of the above, wrapped into the idea that one can cover 600+ miles under less than ideal FE conditions on a maximum-effort day, with a margin left over. Is how I see it. I do not wish to be tied to daily re-fueling, if possible, and prefer to choose carefully the retailer. I trip plan most days, overall, as to rest breaks, meals, etc. A general set of guidelines for the day that let's me pay attention to other points of re-creation as we motor along.

Some days I have no wish to be part of "the madding crowd". Or, with a terrible traffic tie up wish to worry about running out of fuel while idling in summer heat. It's no different than larger propane tanks, an enlarged battery bank or solar power addition, in a way.


The OP is to be commended. That's a bit stressful, but fully warranted, to test the information offered. CUMMINS makes the point that their optional on-board computer monitors are slightly off the first 140,000 miles on big trucks; a pair of converging curves. I haven't tested my "reserve" the same way, but keep a mental note of how far I might travel based on FE to that point (per the type of driving being done). Modern engines may not fully "break-in" for 12-30k miles (FE rises), and I have seen guys claim that their Cummins was still showing marginal improvements at 150k.

I know my overall mpg average, I know the discrepancy between true and estimated mpg as shown me on the readout; can accurately estimate mileage at any given point of any given tank; and hedge my bets accordingly. There is no substitute for recording every gallon and understanding fuel use under a variety of conditions. (Plus I dislike carrying fuel cans except empty).

.
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Old 01-11-2011, 06:59 AM   #10
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I purchased the Transfer Flow tank and appreciate the additional fuel capacity. The stock 30 gallon tank for the short bed was just not enough fuel for a full day's towing.
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Old 01-11-2011, 07:10 AM   #11
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Originally Posted by hickory View Post
Wow 65 gallons of fuel. People cringe when they have to haul 30 gallons of fresh water. They worry what effect it will have on mileage.
What is the reason for the huge tanks?
Fill up when it is cheap, drive longer distances between fill ups, worried about finding fuel?
Not criticizing just wondering.
Hickory
Weight is the least of my worries if I am driving a PSD

I use large capacity tanks to avoid getting caught too far from home and no fuel available. I live in the Deep South where, when hurricanes threaten fuel supplies dry up. During peak season I always keep my tanks at least half full, and top up quickly. FWIW I am running a 1996 F350 and at 14.5 mpg I can run around 800 miles to get away from the storm or get home. I do have a cross bed box/tank combo too that will extend my range to around 1700 miles however you do have to take out a bank loan to fill up

I calculate fuel mileage the old fashioned way using a pencil and paper, last thing I want to do is have to purge air from a diesel system.

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Old 01-13-2011, 06:37 AM   #12
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Every truck's fuel gauge system has its own quirks. It takes experience to learn them.

In my case, my 1996 F250 PowerStroke has two factory tanks for a total of about 38 gallons, or 19 gallons per tank. When either tank reads "empty," I can refill it and get 15 gallons into it, meaning that it still contained about four gallons, or eight gallons for the two tanks. I guess this was Ford's way to provide some comfort before the days of computer-calculated assists.

So, with an average of about 15 mpg towing, that means that I effectively have a reserve of about 120 miles to get to a station after the gauge reads "empty" on both tanks. It took a year or so of towing experience to glean this information about my particular truck.

But all that wasn't good enough for this Mr. Monk. Noooo, because I hate...read, HATE...looking for a fuel station, judging its access, guessing where the diesel pump is, the waiting lines, the details about the use of credit cards, the credit limits, etc and etc, and repeating it EVERY DAY.

So, after a long trip out West where the skys are not cloudy all day and the filling stations are few and far between and knowing my 120-mile cushion is not THAT much and maybe the headwind has reduced it considerably and where the heck is that next little village anyway?... I bought an RDS in-bed 91-gallon aluminum fuel tank for about $500 from Northern Tools.

Now, I get fuel ONLY where its most convenient (read...without trailer in tow) and most economical (read...not in high-tax states or tourist traps).

It sure is nice to not worry about stopping at a filling station every day and have to worry about the implications of that "empty" readout.
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Old 01-13-2011, 10:59 AM   #13
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Same with me and my Duramax. The mpg calculations and range indicator are not to be trusted as being reliable. They have some good functions but nothing is better than tracking your own miles driven and knowing how many miles you can go. I use two odometer functions; one is for total trip miles, the second is the mileage on the current tank of fuel. If I'm pulling, I don't like to get beyond 250 miles or so before refueling (I think my tank is about 22.5 gals, but would have to look it up to be sure). If I'm in the middle of nowhere, you can bet I'm fueling way before that.

Running out is damned inconvenient.

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Old 01-13-2011, 03:00 PM   #14
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Just upgraded to a 4.6 Exploer Sport track tow pack{3:55 axle) at empty on the dash readout of 10 miles ... have about 1.5-2gal remaining...
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Old 01-13-2011, 03:46 PM   #15
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For many years, empty meant you could could 20 or 30 miles. In the late '80's, I borrowed my father's '85 Toronado to make a trip to Key West when we were visiting my parents. This car had a fuel gauge with bars—each bar seemed to represent one gallon. When it was getting low when we returned, I assured my wife, we had nothing to worry about as we could probably get back to Miami where gas was cheaper. When the last bar disappeared, the car stopped. We had a nice walk to a gas station.

In recent years it's been made difficult to top off a tank and the cool electronic stuff that tells you miles per gallon (always higher than reality) and how much fuel you have left are poorly calibrated. On our Tundra, first a light comes on at around 1/8 tank. Before the needle reaches "E", the miles left readout says "0". I have driven 20 or 30 miles after "E" and the tank had 2 1/2 to 3 gallons left. At "E" it can be as much as 5 gal. left.

Perhaps they are protecting us from ourselves so we won't run out of fuel. Maybe they are afraid we will suck dirt from the bottom of the tank into the engine. I have been told it is hard to fill up all the way so as not to flood a filter.

As much as I know none of the warnings are correct, I drive along wondering if they suddenly became correct?

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Old 01-13-2011, 05:29 PM   #16
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My 3500 GMC Duramax has a 34 gallon tank. The DIC is reliable to the extent that it's always 10% off! If it says I'm getting 21 mpg, the true mpg is closer to 19 mpg. If it says I've consumed 25 gallons, it'll take 28 to fill it. With that in mind, I always subtract 10% from whatever miles it says I can run until empty. I keep written records of all fill-ups and periodically I do the math as a check. I've often wondered if a good computer Geek could "tweak" the onboard computer - but I've gotten so used to the dependable 10% error it probably wouldn't be worth it.
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Old 01-13-2011, 05:31 PM   #17
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Perhaps they are protecting us from ourselves so we won't run out of fuel. Maybe they are afraid we will suck dirt from the bottom of the tank into the engine. I have been told it is hard to fill up all the way so as not to flood a filter.

As much as I know none of the warnings are correct, I drive along wondering if they suddenly became correct?

Gene
On pretty much any modern vehicle with a fuel-injected gasoline engine, they don't want you to run with the tank near empty because the fuel pump in the tank depends on fuel for its cooling. The more you run the tank near empty, the shorter the life of that pump is likely to be.

I have no idea if modern diesel trucks have a booster pump in the tank, and I'd hope if they do it's a sturdier design than the ones for gasoline systems.
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Old 01-13-2011, 06:20 PM   #18
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Cracker, ours is off in different directions. It says mileage is about 2 mpg more than reality, but then tells us there's less gas in tank than there is. The computer doesn't even agree with itself.

DKB', I now remember reading about gas cooling the pump—couldn't they design it better? The result is my already inadequate 26.3 gal. tank is more like a 21 gal. tank, maybe less because it's so hard to fill—the back pressure shut off on the gas pumps is set to be more sensitive than it used to be.

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Old 01-13-2011, 07:49 PM   #19
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The digital fuel display on my Transfer Flow tank, which measures the fuel in both my standard tank and the additional 50 gallon tank, is amazingly accurate, as in within a gallon or so. Much more reliable than the onboard fuel gauge.
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Old 01-13-2011, 10:18 PM   #20
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If you want a digital display that you can "trust", consider buying a ScanGauge. This device provides multiple digital "gauge" readouts and allows you to "dial-in" the fuel consumption function.

For our diesel-powered Jetta, I have the device dialed-in to a consistent accuracy of 0.2 gallons for a 15 or 16 gallon fill-up. It's easier to obtain this level of accuracy with diesel-fueled vehicles as fuel expansion is not as big a deal and I can manually vent the fuel system to obtain consistent fill-ups.

For our gasoline-powered motorhome, I cannot dial-in the settings any closer than a 2-gallon accuracy for a 55 gallon fill-up, which is less than a 4% inaccuracy.
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