I have a 1991 F250 4x4 with a 7.3 diesel 5spd. the truck has over 225,000miles on it and runs good. When riding around empty the truck still gets the same 18mpg it alwasy did. However, when I load my 3000lb camper on the back the milage drops to 12mpg. When the truck was new adding the camper only dropped the milage to 15-16mpg depending on the terrain.

Does anyone have any ideas why? Is it just getting old? Any suggestions?

Tks David

 

The most common cause of worsening fuel mileage is the fuel system. The injectors get partially clogged and sorta shoot a streem of fuel rather than a nice mist like they are sposed to. Tired IP's can cause poor fuel mileag as can improper (usually retarded) injection timeing. Of course its always a good idea to check your tire pressure first, even 5psi can make a big diff when you are carrying a lot of weight

 

BikePilot, Thanks for the info. Because of the weight I tend to keep a pretty good watch on the tire pressure (80psi back, 50psi front). Is there any test that can be run to determine if the others are failing? Or is my only option to start changing parts?

If diesel gets any higher this might not matter, I'll have to buy a horse.

Tks David

 

Don't forget the diesel of today is nothing like it used to be either.

The mileage I got several years ago with a worn out motor is nowhere to be seen with a new reman engine in the truck now.

I used to get 16 or 17 often, but I have not seen over 14 in a year or two.

 

No easy way to test an IP that I know of (I think some shops can do it, but don't know the specifics), but any good diesel shop should be able to test the pop-off pressure and spray patern of your injectors and make repairs to them as needed. It seems that most people on this board figure IP's are good for 100k (miles) and anything after that is gravy/borrowed time. That said mine has 125k on it and seems to be doing just fine.

Also check the usual things like air filter, fuel filter etc.

A restricting in the intake or exhaust will hurt mileage (perhpas a tail pipe got dented or a muffler clogged?).

Fuel additives are known to improve mileage. I've not had the opritunity to test them out, but someone upstairs did and found the gains in mileage more than offset the additional cost. I have been running powerservice with is availbe cheeply from wallyworld. If nothing else it makes the truck run slightly better, starts much better in really cold weather and should be good for the ip.


You can add exhaust, headers (if not using a turbo), and open up the intake to get better mileage as well. I'd pump the front tires up a bit more too. That will improve the fuel mileage a bit as well. I run 80 in mine, but even 60-70 would give a little less rolling resistance than 50.

good luck