Just purchased my first diesel last month. Past experience with a borrowed power stroke impressed me enough to finally purchase a 2002 F250 extended cab, short box, 2wd, SRW, automatic with the 3.73 rear. The mileage was 70,000. The truck appears to be bone stock. The carfax report showed normal maintenance performed by Arizona Ford dealers. It also showed that it was barely driven for two years before I bought it.
I had all the filters, engine oil, trans and differential fluids replaced right after I picked it up. I also put on new tires and had the alignment and steering checked.
Then I drove it 130 highway miles at about 80 mph to check fuel consumption. I always manually calculate consumption and this time it came out to 19.3 mpg. Today I ran the same route at 70 mph (2,000 rpm) and got 22 mpg.
Now to the problem. This past weekend I towed a 2,500 lb 7X14 enclosed low hauler trailer containing a 625 lb Harley to Phoenix and back (about 450 miles). The entire route is relatively flat and mostly interstate and I kept my speed at 70 and below. I averaged about 11.8 mpg. I did check to see if the trailer brakes were dragging. The wheels and the backing plates were cold. When I got home, I figured out that the trailer brakes weren't engaging at all because I hadn't set up the brake controller correctly.
I just can't understand how such a light load can drag down the mpg that much. My past experience with a borrowed 1999 F250 crew cab, long bed, 4wd, SRW pulling a heavier enclosed trailer containing TWO 600 lb plus Harleys 5,000 miles also tells me something isn't right. As long as I held my speed at 70 mph or less, I averaged between 18 and 20 mpg with that setup.
I am totally new to diesels. I'm pretty sure I have a problem and I could use any and all advice on what it might be and what to do about it.

 

It was probably the wind resistance of the trailer holding back the mpg.

 

x2 on that. and i wonder if ud get better milage running lower speeds. if u want even better mileage, u may get something from 5w-40 synthetic which i highly recommend as the 7.3 usues oil to fire the injectors. it handles heat better and cold starts, but u may not have cold winters.. but i do haha. also, look into a tymar intake and a dptuner or ts chip custom tuned. everyone seems to love them and the tuning is great. oh, an exhaust helps with mileage also. 4in turbo back would be good. just some ideas as u said u are new to diesels. just remember maintenance is important and dont let fuel filter changes slide. these are much different that gassers, but way more fun!!!

 

Maybe you got a bad batch of diesel? The winter blend won't help.

..biz

 

Moved to the 1999 - 2003 7.3L Power Stroke Diesel forum.

 

I'm really surprised at the you got almost 19 mpg and 22 mpg if you are in a winter fuel blend area on the highway at 80 and 70. I might do around 20 mpg on a long haul in the summer with my truck that is similar except it is 4x4. I usually average around 12 mpg in the summer towing in the 60-65 range.

I just topped off my tank with a mix of highway and town driving with winter fuel and averaged about 12-13 mpg with no towing.

 

2 things come to mind here.....winter diesel really makes the mpg's drop a bit.....and you probably have boost leaks which will drop the mpg's as well....how do the turbo and intercooler boots look? what about the uppies?

 

Congrats on finding a 7.3 with less than 100k.
Ditto on the wind/winter blend fuel issues. Also, these trucks are very hard to fill the tank in a consistant manner. Diesel foams badly, and the vent and fill tubes extend down too far into the tank. If you cruise the forum, you will notice the Hutch/Harpoon mod. Those are in tank mods to help the fuel issues. It often takes 5-10 minutes to get the last 3-4 gallons in. Makes for a difficult time to reliably chart mileage.
Probably need a few more trips to figure out if there is really a problem.
Welcome to the forum by the way. A great bunch that have helped me a lot.

 

Your mileage sounds pretty normal to me.

Steve

 

I am with checking for boost leaks as well, running empty on the flat, your not calling for boost, towing you will be, and if you have a leaking up pipe, a boot popped off, a torn boot, etc, it will kill your mileage.

 

Sometimes too if it's hot and you're towing your fan clutch kicks in and kills your mpg's. If you had a head wind it would hurt also.

 

Thanks for all the advice so far. I will definitely look into the boost leaks and be more careful and observant when filling the tank.
I did forget to mention that I did check in town driving mileage. My in town mileage was a bit over 13 mpg.

 

The lower the rpms at a higher gear = better gas mileage. It will go 80mph really nice, but your putting a strain on your Over Drive and that is not good (the transmissions are one of the only weak links of the truck, treat it right and it will treat you right), stay at 64-68 mph. If you want to raise your mpg/power get a chip or a tuner (keep your top speeds at 70 or below). Never believe the console mpg read out. Fill up to the neck with fuel...not foam.The tank will hold 5 gallons more after the first 'click' off. That there can really throw your numbers off. clean out your exhaust blow back sencor tube. Check for boost leaks. winter fuel. Summer fuel will get better mileage.

Over all, it is really not that bad.

 

Very well put. I agree that it will take a few a more tanks (4-6) to more accurately calculate mileage under various conditions.

 

Only time I've seen above 20mpg (and it was barely above) was going 60mph, no towing on the flat. 75-80mph gets me down to 17mpg.

OTOH generally I get 12-14mpg (not in the mountains) towing a 10k fifth wheel RV at 60-60mph. Go up to 75 sustained and it, well - sucks.

There's too much of a difference between your numbers, makes me wonder if something has changed with the truck (like what has been said, boost leak, etc) or if maybe it wasn't a complete fill-up. So I'd try more tanks and check for some of the common problems listed above.