So I had a 70 f100 with a 390 and 4 barrel carb that got around 10 mpg. I've heard people say that the 360 was a gas hog but I couldn't imagine it to be worse than the 390. I have the stock 360 and 2 barrel now. I have replaced most of the fuel lines in it and I know I don't have a leak but I'm only getting 5 mpg. Is this about normal or do I have a problem somewhere?

 

If it isn't a gas leak, sounds like the carburetor and engine needs a major tune up.

Even so, if the truck is loaded or unloaded, or travelling on level ground or, is going up or down a hill (with a tail wind), about the best it's going to get is 10-12 MPG.

 

I didn't think you could use the words "360" and "MPG" in the same sentence.

A 360 does get worse MPG than a 352 / 390. (I believe it has to do with the stroke.)

Aside from that, 5 MPG is a little too low. Your MPG could be affected by your engine not performing well, as ultraranger said. A tune-up may be able to help that. If you can't find a leak anywhere, it could possibly be your driving habits. What kind of driving are you doing, city / highway? What kind of transmission are you running? I do believe you should be getting around 10 MPG average. (At least that's about what I am getting in my 67' 4x4 with a 360.)

I have heard of 4 barrel performance 390s getting better gas mileage than mileage built 360s. I also was told that 360s make up for it in there reliability because they are not powerful enough to hurt themselves. (Not sure how true this information is, just coming from what I have read from other forum members.)

 

I the truck is a rear wheel (2 wheel drive) auto transmission. I was considering rebuilding the carb but wasn't sure if that was the issue or not. I guess I'll also tune her up and see if that helps in the mean time. Thanks for the feedback everyone!

 

I've owned several and they were usually 12-13 mpg trucks, but mostly 4 speeds. I have seen a best of 15+ on one with headers. I've seen no measurable difference in the mileage on 360s and 390s.

 

About 8-10 is as good as it gets with a 250 FE. The whole thing about a FE is keep it turning slow. If it is a stump puller with 4.11 rears 5-6 may be about it.

At least gas prices are lower just now.

John

 

The one I got 15+ with was a 74 F250 4x4 with 4.11 gears. But in all honesty that was with 70s gas and 55 mph speed limit. The last FE I had was a very tired 390 in my 69 F250 crew cab with 3.73s and it always ran around 12-12.5, with recent gas and speed limits.

 

Sir, A Ford F250 4wd 4.11 gear ratio can not get 15 mpg even when being hauled on a trailer. If that feat were possible someone somewhere would be all over it trying to duplicate it and make a sheet load of money.

I don't meant to call you out, or try to make you look bad, but I have been around these ol Fords for a long time. I have owned them, driven them, hung out with others that owned them on this forum. Some info was added in wrong.

There would be 25 different venders selling this kit or that kit trying to make it happen again. You could be a wealthy man should you figure it out.


John

 

Pretty sure I've been around just as many as you. I've owned at least 40 and ran my own shops working on literally hundreds. Last count I had owned and driven at least 17 F250 4x4s with FE engines from 332 to 428 but mostly 360s and 390s. Was the 15 (actually more closer to 15.5) representative of a long term average? Absolutely not, but it was filled only to the pump shut off at the same pump. I owned several F250 4x4s with 360s and 4 speeds 4'10 gears and back when the speed limit was 55, I generally got around 13 highway with most of them. One 74 I had would average 11 pulling the stock car cross country, figured over several tanks and not just one fluke fill up. If yours only get 8-10, that's probably some reflection on your driving habits or ability to tune one.

 

I haven't owned nearly as many as you. I am basing on F100 2wd 3.25 rear getting 12-13 tops, and you are claiming the heavier F250 4wd with a much lower ratio 4.11 getting 15. It doesn't add up sir.

You would be wise in sharing your secret, because a sheet load of money can be headed your way when others can achieve that kind of mpgs.

I do not want to make a bitter argument of this, so standing down.

best


John

 

You may have a broken abacus. I'm not even doing that poorly with my 460.

 

Jo, any single tank is not representative of long term results and I didn't say that, only that I had gotten that as a best. Maybe there was a tail wind. Even just heading into or running with a 25 mph wind will make a huge difference. Even with my more modern vehicles I can pick up 1-3 mpg by just slowing down from running 80 with the fast crowd to about 62-65, so lots of different things factor in, but you know that.
I'm sure there are plenty of people who would disagree but I don't think the diff gear ratio makes as much difference as some people think. It takes the same amount of horsepower to propel a vehicle whether it's at 2200 or 2800 rpms. I've seen no measurable difference in the fuel economy of these trucks with 4.10s and 3.73s. But then I never tried both ratios in the same truck either.

 

My apologies to the original poster for taking this thread down a rabbit trail. There are a few good tricks to fine tune fuel economy, that's for a different thread. Ford actually had some TSBs that applied.

 

F250's use Dana 60's, 1967/79 2WD available ratios: 3.54 - 3.73 - 4.10 - 4.56 - 4.88.

So don't assume that it has 4.10's, because it could be better or it could be worse.

If driving 60 MPH or faster, MPG drops off by at least 40% vs driving at 55 MPH

When "Tricky Dick" was in his 2nd term as prez, he mandated the double nickel (55 MPH) in an effort to improve MPG

This occurred during the 1st Arab Oil Embargo (1973/74). Another occurred in 1979 when Jimmy Carter was prez.

 

I think almost every F250 4x4 I ever owned except 2 were 4.10s I had a 75 with full time and I think it was taller, cant remember for sure and I had a 76 with the 4.56