My 89 F150 300 Straight 6 is horrible on gas!!

I got better MPG with my 4.10 geared 7.3L Diesel! Then again it is a 5 speed.

The F150 has the C6 3 speed auto, and with 3.55 gears according to the door jam sticker (19), it really sucks up the go go juice!!

RPM's sound pretty damn high on the highway I'll tell ya that! Sounds like it's turning near 3000RPM at 60mph.


What do y'all see with your 300's as for MPG??

I discovered i'm getting 13mpg on the highway.

 

I got around 15-16 from what I recall with mine, with a 5 speed. I could be lying though, since I sold it 4-5 years ago.

 

No OD and 355s wouldnt help MPGs much.

 

300, C6, 3.55, 33/12.50/15 9mpg regardless.
Yes, I have done the calculations NOT relying on my gauge cluster mileage.

 

I honestly don't know and don't care.

1987 F150, 300, with 4 speed overdrive manual tranny. I usually haul junk or do side mechanic work to keep decent gas in the truck, so yea, I don't give a crap if it does bad or good. It pays for it's own gas anyways most the time haha.

 

GET VACUUM GAUGE

I used to get that 13 when I add vacuum gauge now I get 16-19 but RARE is 23 mpg that required lot patient.

 

I'm getting 13.5 mpg, mostly back roads, some highway. I changed the air and fuel filter in hopes of gaining one or two to the gallon.

 

im getting around 12-14mpg around town and 18-19 hwy. mine is a 5spd. believe it or not it used to be lower, but i seafoamed mine at the last oil change and when i was doing some gaskets, and it went up around 2mpg overall. at 70mph im turning about 1800rpm.

 

yea i get 12-13 no matter where im driving its a 5 speed but it might help you if you get a little higher gear ratio in the rearend of that truck

 

But have you recalibrated the speedo for those tires? if not the odometer is WAY off and that's why the milage looks so bad.

 

IDIDieselJohn, when I first got my truck in December, it was getting between 12-13 hwy. I changed fuel filter, plugs, intake/ exhaust gasket & clutch just recently. I'm getting 15.4-16.6 hwy. Mine is a 4x4, 3.08 & 5 spd w/ 265/75R15 tires.

 

How does adding a vacuum gauge help

 

Fishforlife2007: " at 70mph im turning about 1800rpm."

OMG--------what size tire and differential ratio gives that low RPM? 2.75 with 31 inches? With my 31 inchers and 4.10---I am turning 2500 RPM with my 5 speed and 5.0. And getting middle/ high teens MPG.

 

I didn't know that having bigger tires would effect the odometer if the speedometer isn't recalibrated. I gotta fix mine if thats true

 

My relatively stock 87' 302 gets 23mpg @ 65 mph. Good Cylinder compression psi, further advance of base timing (like 16 BTDC), and an upgraded Ignition system that allows greater spark kernel exposure (side gap copper core plugs .056/ .044 is stock) are the key elements & stick w/ 87 octane. My HC (hydrocarbon) output is .01 PPM. Average for my yr/ engine is .14 PPM. Suggesting little fuel is going to waste! It can be done, but all your ducks have to be in a row. Also a 180F thermostat. If your only running stock base time (10 BTDC), I 'd stick w/ a 195F. My best MPG is just below 2K w/ stock gears & tires.