Ok fellars, here's a tricky one.

My 1992 F-150 w/ a 300/5spd gets a flat 15mpg CITY, and then, out on the highway, it gets 13.5mpg......W-T-F?

I have so far replaced-

Plugs-Autolite Coppers
Wires-Duralast
Distributor Cap & Rotary Button-Duralast
Front Brake pads-Duralast Medium Grade
Inner/Outer Tierod ends, sleeves, etc-Duralast

Also have changed the oil with Castrol GTX 5W30 and a Motorcraft Filter....And changed the air filter also......The only things I haven't changed yet are-

Transmission Fluid
Differential Fluid
Rear Brakes-Altho I have new Duralast brake shoes, spring kit, and new drums to go on.....

Still yet though, I do not see how that the fluid changes alone would give me approx. 7-8mpg on the highway by themselves alone....

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Now on the other hand, my 94' F150 300/E4OD got 15-16city, and between 19-20 on the highway......The ONLY things different between the two are-

The 92 is a manual, and has 165k miles
The 94 was a automatic, with 6 leafsprings in the rear, the smog emissions crap removed, and 266k miles....

Both trucks are longbed, 2wd with only the front gas tank working...

If anyone has any input, PLEASE speak up, because this is unheard of, and frankly ***-backwards mpg readings.....

Thanks all-

-Wes

 

Are the gears in the rearend stock? what rpms are you turning on the highway?

 

Yes, it's very possible, as my F350 crewcab gets the same mileage pretty much no matter what.

Locally, where I don't need to accelerate quickly, I typically shift just above idle thus I'm mostly at a very low RPM most of the time. I have enough engine torque to idle around town at 24 mph in overdrive. That balances out to the same MPG as turning whatever rpms at 65-67 mph on the freeway.

The question is, has your truck always been like this, or just recently? If it's the latter, then it's something to adjust, fix, or repair whereas if it's always been like that it's likely to be "is what it is".

 

The rear gear are the stocker 3.08's, and my tach shows approx. 1,700-2,100 rpms.....that is running between 55-70mph......

-Wes

 

Quote: "Both trucks are longbed, 2wd with only the front gas tank working..."

Are you sure the tank is not pumping fuel into the non-working rear tank?

 

That's easy: acceleration is what consumes more fuel, and start/stop traffic requires just that. Highway driving can be more economic if you archieve a good speed and manage to maintain it for long periods. There is a curve that relates speed and fuel consumption, once you reach a certain speed (around 50-55 mph in our trucks, depends on the gears) consumption starts to pick up again.

 

Yep, the 92' doesn't have a rear tank, the P-O removed it......lol

-Wes