F350 gas mileage

ford
f350

#1

Have a 1992 F-350 4x4, 429 V8; auto transmission with o/d. I tow a fifth wheeler. Without camper if I stay under 50mph I get 11 mpg; doing almost anything else gets 8 mpg; towing brings it down to 6.5 mpg.How can I increase gas mileage. I drive with a light foot and slow start and stop.


#2

What year is the 429 engine out of ? The newest I see is 1973.
A carburator overhaul could be in order.

What transmission is in the truck now ?
If it’s the old C6, that’s only a three speed and putting in an overdrive tranny would give you one more gear.
The AOD for a 460 might fit as the 429 was the little brother to the 460 back then.

Then, what is the ratio of the axles ?
With bucks to spend you could change those too , but at the expense of your low speed pulling torque.


#3

You’ve got a one-ton 4WD pickup with a 5th-wheel setup. Mileage was not a concern when the truck was built. I doubt you can do much to improve it now.

You say you have a 429 engine. Am I to assume you installed an older carbureted engine? 429 hasn’t been available since 1973 or so, and then only in passenger cars.

Are your tires/wheels stock size?


#4

The best way to increase fuel economy will be to get rid of it in favor of a diesel truck. They do better on fuel than a big block gas motor and tow better.

Are you sure you don’t have a 460? If you do have a 429, swapping in a 460 may actually help. It’s actually meant to perform these kinds of jobs.


#5

I would first check the odometer to see if it is accurately measuring the miles traveled. If someone substituted oversized tires, the odomter would be registering fewer miles than actually traveled, while you effectively have a higher gear.

When you acclerate from a stop sign, count the number of shifts to be certain that you are actually going into overdrive.


#6

7.5L V8 engine?

You aren’t going to get any better fuel economy than you’re getting now. The best way to up fuel mileage is getting something that’s designed to get better mileage and just using the truck for towing the 5th wheel. A brand new F-150 will pull almost as much as your 92 F350 does now(11,300 vs 12,500), AND will get better mileage than you’re getting with the 5.4L V8.


#7

However, the difference in price between the 1992 F-350 and the new F-150 will buy a lot of gasoline


#8

Surely you mean a 460, which is basically a stroked 429. These engines are not what you would call fuel misers anyway.

Keep it tuned up, keep the tire pressure up a few pounds, and possibly tweak the ignition timing a bit.

This truck should use the TFI module and sometimes if these modules are replaced the installer may remove the dist. or turn it. Not using the proper procedure when checking and adjusting the timing can throw it off by a mile.
This means that the SPOUT connnector MUST be disconnected when setting the timing. Adding 1 or maybe 2 degrees of extra advance in will help it some but I would not go more than that.


#9

I’m dumb; it is a 460; the engine and tranny are stock.I’m running 16.5x 33 tires which were on vehicle when I bought it; 16’s are standard.


#10

I’m dumb; it is a 460; the engine and tranny are stock.I’m running 16.5x 33 tires which were on vehicle when I bought it; 16’s are standard.


#11

Thanks. Will talk to my mechanic. I rewally do love the truck.I’d drive it a lot more if I could get a little better mileage.


#12

It is too bad that a 2 speed axle isn’t available for pick-up trucks. This would be a perfect solution–one ratio for normal driving and another ratio for towing.


#13

OK. Your tires are just a little oversized from stock.

Does it seem to have adequate power? You could try to open the exhaust a little with an aftermarket system. Also have a competent mechanic do some testing on the fuel and ignition systems. Unlike 1996 and newer, these systems don’t always turn on a check engine light when there’s a problem. Things like ignition timing, oxygen sensors, MAP sensor, and coolant temp sensors can fail while still being “in range.” Fuel pressure could be high too. Have the same guy–or a transmission guy–make sure the torque converter is operating properly.

Even with all this, you might improve your mileage from 8 to 9. :slight_smile:


#14

You are getting good fuel economy for that type of truck. Some Ford speedometers could be off. If yours is showing four miles per hour less than you are actually doing, you could be getting better mileage than what you think.

Using a stopwatch, start it at a mile marker. With your speed being 60 MPH, you should do exactly a mile in 60 seconds. Each second that you are off will tell you exactly how fast you are going.

64 seconds to do a mile means that you are doing 56 MPH. 56 seconds means 64 MPH. Your odometer will be off proportionately. Each second represents 88 ft. Four seconds would be a 15th of a mile. You would be .67 miles off from the correct MPG figure if you were off by 4 MPH.

The speedometer is probably correct, but you never know unless you check.


#15

Your tires are part of the problem.

First, you don’t have enough load carrying capacity in your current tires - and that is translating into drag.

The second problem is that your tires are not the latest technology. 16.5 tires are rapidly becoming extinct and what is currently on the market was not made with rolling resistance in mind.

So your first step is to find a junkya …er… auto recycling center and find a set of wheels to fit your truck. The next step is to fit the proper sized tires on it. As a guide to this, you’ll need to consult your vehicle tire placard (It’s on the doorpost!) which will list the original tire size and the preoper pressure for that size - and if I remember correctly, it will also list the rim size.

I did a quick look at Tire Rack and they list 2 tire sizes: LT215/85R16 and LT235/85R16 - get the larger one. Not only that, but there are some tires listed as LRR (Low Rolling Resistance!) Unfortunately, all terrain tires of this type are never going to be LRR - which kind of negates the 4X4!

Post back if you have more questions!


#16

8-11 MPG unloaded and 6.5 MPG towing is pretty much all you cam realistically expect with a 1 ton 4x4 with a big block under the hood. The current tires you have on are a bit larger than the stock sized tires and if you haven recalibrated the speedometer to reflect that, then your MPG figures are a little off as well, not by much but around the order of 3-5%.

There really isn’t much you can do to significantly improve the mileage that’s not cost prohibitive or involves a reduction in the capability of the vehicle. My advice is just to live with it.


#17

Replace the thermostat if it’s over 5 years old.


#18

That much is true, but they asked how to save fuel, not how much it’d cost. :stuck_out_tongue: