I was just given my first diesel, a 91 F250 7.3 with only 156K miles from my father in law. Prior to getting it he had changed the hoses and belts and the air cleaner is new. The first tank of gas I got 220 miles out of it. Which by the records indicate that this is average in the rear tank. The next four I have only gotten 150 miles. I started using Lucas fuel treatment two tanks ago. Is there anything I can look for or replace to get back up to the average 12-13 mpg?

 

you had to have done somethig. could be the way you drive.be easy on the gas or pay the diesel gods. i run diesel kleen through mine. it seems to be good for 1-2 mpg. check your fluids and watch how you run it. a load will nock the mpg down.

 

I try to be as light as possible. Now my wife on the other hand may be a different story. When should the injectors be replaced? I am trying to figure this out before I hook up a horse trailor and find it gets even less mpg. Could an old muffler cause this problem?

 

no, unless i suppose its plugged, which Ive never heard of.

 

Have you checked the air filter? You are sure it has been recently replaced?
Is there any black smoke at all?

Do you mind spending money on it (700 plus shipping)?

 

what in the world costs 700 dollars??? what kind of air filter is this?

 

Try to acertain when the last fuel filter was changed, when did you last drain the filter for water. Fuel additives are good and will clean and lubricate and in some case up the cetane level. Use good quality fuel ask here for recommendations from people local to your area. If the IP and injectors are original then consider replacing them if the MPG is still low. What is the rearend gear ratio, what tonnage will you be towing.

Please refer to the fuel as diesel or fuel, if you accidently put GAS in it this would lower the mileage and do a nasty on the pump too.

 

First thing, do you have a tachometer?
Do you know the gears in the axles?
What transmission?
2 wheel drive or 4x4 or dually?
How fast do you drive MPH?
Are you in flat, mountains, high elevation?
What size tires?
Is there any black smoke? When?
So many things affect mileage that you have to say more than my mileage dropped.
Also when do you fill up? At 1/4 tank or when it is empty the truck stops running?
Has the truck set for a while and you are just starting to drive it again?

Then I will say that the only way to get an acurate MPG is to fill the tanks, get a receipt showing gallons, write the mileage on the receipt, drive till you need fuel again, fill the tanks, get a receipt showing gallons, write the mileage on the receipt.
After you do this several times you can figure the mileage for each fillup and then average them to get your average mileage.
Pulling a trailer, hauling a big load, driving fast, running the tach to 3000 RPM on every shift, or foot on the floor a lot will all drop the mileage real quick.
Also I find that my engine likes some fuel a lot more than some others. Find a place you get the best mileage and fuel there always or fuel at the same brand fuel stops.
My truck hates Exxon fuel (no power or mileage), it likes BP (great mileage and runs great) Chevron (pulls good mileage stinks) and so on.

 

I only get maybe 10 mpg with mine, but my pump is turned up slightly and my right foot weighs a ton. I also have a 3 speed with 4.10 gears and small tires so I run about 3500 rpm at 70 mph. I'm going to do a gear swap eventually to bring down the cruising speed down a couple notches.

 

swap gears if you want to, but a 5 speed will do wonders also. i have a zf5 4.10 banks sidewinder, i only run about 65 i pull about 2300 on the tach to get about 15mpg

 

I am with dave, the speed you drive at can make a huge difference. My truck gets 21mpg empty at 55mph and 13 at 70mph.

 

'89 F250 SC 4WD 3spd auto, 3.55 - about 12mpg in hilly/mountainous terrain.
I run about 60 on the freeway - that equates to a tach reading of about 2600rpm with this tranny/rear end.

When my wife drives (who likes to gun it), mpg drops about 1mpg. I pull a light weight Coleman popup trailer (about 2,000#). The truck doesn't know it's there and I see no difference in mileage while towing.

 

[QUOTE=Dave Sponaugle]First thing, do you have a tachometer?
Do you know the gears in the axles?
What transmission?
2 wheel drive or 4x4 or dually?
How fast do you drive MPH?
Are you in flat, mountains, high elevation?
What size tires?
Is there any black smoke? When?
So many things affect mileage that you have to say more than my mileage dropped.
Also when do you fill up? At 1/4 tank or when it is empty the truck stops running?
Has the truck set for a while and you are just starting to drive it again?

The truck is a 4.10 axel running P235/85 R16 tires 2wd single axel. I usuall drive around town or 65 - 70 empty on the highway. Which this sounds like can be the issue in itself. The tach never goes over 2700 rpm even durring accelleration. There has never been any smoke. I live dead center in the Central Valley of California so we are truly flat, I have yet to take it into the mountains. THe truck is driven every day. When I do fill up it is between the 1/4 tank and empty;however, I use the reciept as the gauge for fill up. Which I fill between 17-18 gallons. Actually the truck did sit for a couple of months. Oh, and a new fuel filter was insalled last 2 weeks ago.
I hope this helps out because I baffled.
Thank
Ryan

 

The 4.10 gears and the 235/85-16 tires and 65 - 70 MPH is where a lot of fuel is going.

Do you have a manual 4 or 5 speed or an automatic 3 or 4 speed?

Let me ask it this way, at 60 MPH what does your tach say when you are in high gear?

 

The tranny is an auto 4 speed that at 60mph is around 2200 rpm.