It happened again:

[Cyrus]

Have any of you with 2005 Ford diesels experienced fuel mileage increases about every 20K miles on the vehicle. I tripped 70K miles a few weeks ago and noticed an increase in fuel mileage driving local. No long trips or pulling camper since it tripped 70K. It so happens for the last 20K miles or so the fuel gauge drops ¼ tank for every 100 miles but for the last couple thousand miles I am more then 100 miles per quarter tank so it was easy to notice the increase. I have kept a record every time I fill up and the MPG calculation agrees also. Local driving I was averaging 13-15 MPG now around 16-17 MPG. I am driving the speed limit 55mph etc. For the last three fill ups this has held true.

[richfaa]

We have the 08 F-350 and have noticed a increase at @ 6K, 12K and 16K. We had all the updated flashes done last month. We have a early job 1 build and we did note a increase with the flashes.We now have 18K on the truck and it runs better and better with increased mileage. We are looking to see if we do any better MPG towing home from Florida.

[skypilot]

I don't have a Ford now but my Dodge's have worked much the same -- at about 10K the mileage increased, then again about 18K it went up. Traded the last one before it hit the next point but reading on the dodge forum indicates I can expect my new one to increase at about the same 10K points for awhile. I imagine part of it is break-in, and then some of it has to be programming. Interesting to note the increase at that high of mileage though. Also, when your area switches back to summer blend fuel (gets rid of the #1 diesel blend) it will increase as well - #2 diesel has more heat (more power) than #1 -- about a 10% (or 1 to 2 mpg) increase might be gained according to what I've read and the decrease I experienced when going from Summer to Winter blend this past fall.

[Bill-N-Donna]

I’m at almost 320,000 miles and I’m getting around 13 local and 15 on the highway. It would be nice if the incremental increase kept on coming with the higher mileage! I didn’t own it with the first 300,000 miles so I can’t say if there was any difference then.

[Cyrus]

Bill,
I hope I can get 320,000 miles on my 6.0. With an increase of a mile or two every 20K miles I will have to put a second tank on the truck the catch the fuel it makes. Would be nice would it not.

Rich,
Don't rush north yet! We had rain with snow mixed into it today in VA. Fredericksburg, VA radio said temperature dropped 15 degrees this afternoon in a matter of minutes. Talked to brother-in-law near Pittsburg, PA and he said it was cold, windy and some snow up there today. My camper is still winterized.

[Clyde n Deb]

"I will have to put a second tank on the truck the catch the fuel it makes."

I need more info on this theory.............

[Cyrus]

Just filled it today and got 17.7 MPG for 315 miles of local driving.

[Dean A Van Peursem]

You newer Ford Diesel owners better be careful, pretty soon you are going to have to stop every so often and drain some fuel out of the tank. :-) We run a 2003 Ford 7.3 Liter Diesel engine and it has always provided pretty good mileage. If I don't go over 60 MPH empty I'll occasionally get 20 MPG or slightly better on Interstate driving. We quite often average better than 12 MPG pulling a heavy, late 2006 3400RL on our yearly 1600 mile trip each way to and from AZ. However, 40 MPH headwinds and rain seems to have a negative impact on that. :-) At about 87,000 miles right now on the truck. It has been a completely dependable and trouble free truck so far. Knock on wood. At least it hasn't caught the 2006 3400RL disease yet. And we did get the "Warm and Toasty" option on it! :-)

[Art-n-Marge]

I have notice a swing in calculations, too but I only have 45K miles on my F-250. I haven't given too much thought on those trip computers calculating mileage because I don't know what the algorithm is. (How do you like that word "algorithm"? It means the factors and mathematic calculations used by the trip computer).

In the computer engineering industry we called them variables - things that can adversely affect what otherwise would be exact science. In the case of our vehicles there could be a bunch of stuff that causes these swings - temperature, where you get your fuel, wind, condition of the vehicle, when you get your oil changes, your driving style with or without a load.

I typically get 19-21 mpg with no load on the open freeway. I went crazy when I actually got 26 mpgs on the same trip I use to monitor my fuel usage! But I have not duplicated it. But that day there was NO traffic (very unusual for So. Cal.) and I drove pegged right on the speed limit (70 or 65 depending on the freeway). I usually drive a little faster (shhh, don't tell anybody, but that prevents being blown over by semi-trucks blazing by me) and get 19-21 mpg.

Bottom line, I wouldn't worry about it. Use the old pencil, paper and calculator to do your own calculations and you can't judge it on just one week's fuel tank or a single trip. I monitor things between oil changes (5,000 mile intervals) that's where the 19-21 mpgs comes from. The trip computer is only just a tool to satisfy a customer's checklist that wants one. Yup, this gadget dude had that gadget on the shopping list. Actually it just happened to be on the truck I bought and I just said, "Cool!".

It will still be interesting to hear everyone's experience. I do think that after 75,000 miles or more and the diesel is finally broken in, things might settle down. Or the computer will break and I'll just go back to pencil, paper and a calculator.

Cheers,