Poor mileage on the 1997 F150 4.2L V6

[03trubluGT]

Just did a mileage check on the F150, the motor has almost 2k on it now (rebuilt).

I'm getting almost 16 mpg, and I'm thinking it should be better.

I went from a P235/70R/16 (29" diameter) to a P265/70R/16 (30.6" diameter) tire.

The stock gears are 3.08 and I want to go to a 3.27 or 3.55 gear to get the truck back in the power band. I'm thinking the .308s are a little low for that tire.

Using a couple of online calculators, I found this

P235 tire with 3.08 gears equal about 1749 RPM at 70 mph
P265 tire with 3.08 gears equal about 1657 RPM at 70 mph

So, I figure with 3.27s:
P265 tire with 3.27 gears equal about 1759 RPM at 70 mph

P265 tire with 3.55 gears equal about 1910 RPM at 70 mph

Should I go with the 3.27s to return to "normal" or grab the 3.55s and not fear the 150 RPM increase.

My son will soon be driving the truck to school and to hockey practice (Mansfield to Farmer's Branch 3 days a week, and from Mansfield to Frisco one day a week).

I want the best gas mileage I can get since I'm having to foot the bill.

Thanks for the input.

[dville_gt]

you correct the speedo when you changed tires, could be low mpg because you are calculating off the wrong # of miles

[dville_gt]

@ and indicated 60mph you are actually moving 63-64mph but only putting miles on like yo are doing 60mph

[03trubluGT]

you correct the speedo when you changed tires, could be low mpg because you are calculating off the wrong # of miles

Didn't think about that. I didn't change anything but the tires. If the speedo is reading 5.7% too slow, then I guess I'm travelling 5.7% more than I'm showing on the odometer, so I guess 16 mpg is really about 17 mpg.


When the speedo is showing 65mph, the GPS shows I'm travelling 69-70 mph.

[Cobraman]

I only got about 17mpg in that same truck. I was wishing I would have gotten a v-8.

[dville_gt]

when i saw cobraman had responded i figured he suggested fo five sixes

[80coupe]

and ripped torque boxes!

[dville_gt]

plus some motors take 3-5k miles before they get their optimal number of mpg's.

you might gain some mileage with gears but a cost analysis would probably dictate that the repayment would take a while and if you end up not getting any additional mileage it'd really suck.

[03trubluGT]

I only got about 17mpg in that same truck. I was wishing I would have gotten a v-8.

I was hearing about the 4.2Ls getting about 20 mpg.

[UserX]

Leave it as is if you want the most MPG, changing the gears will only make it worse.

[JC316]

I was hearing about the 4.2Ls getting about 20 mpg.

Uh huh and the commercial for the 86 F150 I6 said that it got 30MPG. Funny, I had that same I6 and got 17MPG with it. 17 seems about right for a V6 truck.

[svauto-erotic855]

Is the 16mpg with you or your son driving? Do you have a scanner that will let you look at live data from the o2 sensors? Have you checked the fuel pressure while the engine is hot and not running to see how long the system will hold pressure?

I use this to see if I am in the ball park mileage wise when driving an unfamiliar car or truck.

http://www.fueleconomy.gov/feg/findacar.htm

That is a good looking truck by the way.

[Vertnut]

I have a 5.0 Mountaineer w/177k on it w/3.73's and I get avg. 17mpg. I've heard the 6cyl motors work a little harder in the trucks.

[franks]

mine only got 15-16 with the 4.2 and 5 speed combo.

i hated that truck, got a ranger now and love it. 28 mpg

[carbd89sleeper]

Sell it and buy a 4 banger ranger