Hi, I have a 1970 F100 Sport Custom, 302, 3 speed manual, 3:55 rearend (i think) I am having a real issue with the mpg's. When I first bought the truck it was getting around 8 to 9 miles per gallon. Since then I have done a vast array or tune ups to get her running better and I have managed to get it up to 13 mpg. I had a 2bbl carb rebuilt for it, it came off a 1979 LTD. If anyone can give me suggestions on how to improve my mileage I would appreciate it as i would like to get her up to 18 mpg or better.

PS, what is everyone else getting for mileage?

 

I have almost the same truck as you and that is what I am getting, and darn happy to get it. There aint a whole lot you can do, I think a 4bl helps alittle and better exhaust, go the more complicated way and put in better gears, but 3.55 aint that bad. I think that 18 is a pretty big stretch but what do I know I have been wrong almost once before (I thought I was wrong, but was actually right).

 

I have a '72 360 2bbl with a C6 and 3.00 rear axle. At 134,000 miles the engine has never been apart, and uses no fluids, doesn't smoke or leak a drop. It's the darndest thing I ever saw. When I first got it I would easily get 17 mpg on regular at 60-65mph on the freeway, but since I added power brakes, power steering and AC it has dropped to about 14.5 or so highway. If I try to push it much over 70mph it begins to eat the gas. The old guy I bought it from kept a log book of every little thing he bought or did to it and jotted down the milage. He was the original owner and treated it like a baby, only selling it because he turned 87 and was going deaf and blind. I have stock tires on my truck if that matters any.

 

Hey Scott,

Here is one of my old replies in another forum.

I thought you might like this info.

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Things that improve fuel economy:

The general condition of the engine itself (rings/valves,etc)

Engine in proper tune with all parts operating correctly.

Clean air filter

Clean rotor and contacts in dist.

proper inflation in tires

less stop and go driving

proper gasoline per application

fresh gasoline(usually acquired at a very busy gas outlet)

Higher gear ratio (2.75- 3.00:1)

Keeping your foot out of the accelerator(EGG under gas pedal works)

Having the Proper thermostat in engine.

Weight that is being hauled.

Not having "Wind Drag"

SHORT warm-ups (not letting the just engine idle away)especially with the choke on.

 

Your above average mpg's for these old trucks. I get 8-12 or so with my 250 w/390 and a small 480cfm 4v, my beater 4x4 gets 7 or 8 tops even going down hill!!!

I got 20+mpg once...... going down the other side of a mountain pass!!!

 

I have a 72 F250with a 390 auto and A/C. The parts stores used to have 160 and 180 degree thermostats listed for the application. I always picked the 180. I now see a 192 degree thermostat listed in Dennis Carpentor. Is anyone using a 192 degree thermostat? Have you noticed any difference or any benefits?
Joe

 

I run a 195* with no problems and I also better performance than the 180*

 

Welcome to FE Ville, they do not like to pass too many Gas Stations, at least that's the general consensus. They' were created and used at a time when gas sold for 25 cents a gallon and if you think ours are bad you should talk to some 440 Mopar guys.
I've been driving mine with various engine configurations for 14 years (Incl. one cross country trip from CA to WI) and even with stock 352 (2bbl) I barely beat 12-13. With built 390 and an AOD tranny and 3.55 rear, I can get 10-11 on the Hiway. Surprised no one mentioned bed covers - they help, not sure how much, but it's gotta help some.
If MPG is your thing, I'd look for an I-6, or a 302.

 

I just installed a tach on my truck and it runs about 2500 to 2700 RPM at 60MPH. I think thats pretty normal isnt it? What should it be idling at? (1970 302)
I recently purchased a set of holley headers and i will be running 2 1/4 inch dual exhaust how much could this help mileage and horsepower?

 

Idle for my 72 F100 302 is 800 RPM, not sure about an auto, but i think that it is 500 RPM in drive. It should be on the orange sticker on the drivers side valve cover, along with other specs like timing and spark plug gap. I also hear from the general conversation forum that leaving your tailgate up is better than leaving it down as far as drag and MPG... not much better, but better.

 

How much would it help MPG having those extras? More flow usually ment more gas could get in and out whenever I beefed the exhuast on my trucks. Thats just my experience though, some people claim good results with mpg improvement using hedders.

 

Look again, I presented the supporting engineering data that was mis-quoted. One other thing. driving with the tailgate 1/2 way open gives the best gas mileage! I gain 1 1/2 mpg on my CK.

 

I can get 27 mpg...

That is when I leave the truck home and take my car because I'm not towing or hauling something that won't fit in my car.

Otherwise I get 8 or 9 mpg with my 72 F-100 with a 390, PS, PB, automatic. I'm honestly not sure if it's a C6 or what my rear end is.

 

You'll have to reduce your cruising rpm to get better mileage. Either taller axle gears which can be accomplished with taller wheels & tires, at least 3.00, or an overdrive.