Gas Mileage is poor
 

I have a 69 shortbed Chevy stepside with a 250 and factory carb. In fact it's all original but for new paint and body work. I get 11 1/2 mpg. I had a 70 stepside with a 395 and got about the same mileage. Is this all I can expect from the 250 6 cyl engine? Maybe I used too heavy a paint:( ?

I have a Holley 8053 Economaster I was thinking of putting on. Would this help or be a mistake?

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What's the rear gear ratio. That may be some of the issue.

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what cst10 said, with that, pretty much the only way you're gonna get decent gas mileage is an ls swap with a 6speed and around a 3.08 rear gear, goin 6.0 with 4l80 and 3.73s on mine. Interested to hear how others have squeezed mpg with these trucks

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My 1972 stepside with 250 I6, 3 speed on column, 4.11 gears, and 1-barrel carb gets about 10 mpg. You are not alone.

I plan to switch the rear end to a 3.73 gearing but that's the only plan I really have. I'll keep my old gearing in storage just in case I ever need to switch it back.

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That 250 has to work pretty hard to push a heavy, box-shaped truck around. The 396 had plenty of torque, so it wasn't working nearly as hard.

Smaller displacement doesn't always mean better fuel mileage.

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When these trucks were built, gas mileage wasn't a concern with gas prices being in the $0.20 to $0.25 range per gallon. They were built from real steel, very little if any plastic and were meant to haul any and all items. My '71 4x4 came to me with a 350 V8 & 2 BBl carb. Seemed 11.5 per gallon was best it would do, 4 speed and 3:07 gearing. Now it has a 350 with 625 CFM Edelbrock carb and Performer intake, 350Th trans. Haven't checked mileage in a long time but probably does worse now as truck performs better and the foot is heavier, LOL. Your in the ball park with lots of other folks even with the inline 6. As truckster mentioned, that I6 is working to move your truck down the road.

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You have to PAY TO PLAY ! Want gas mileage buy a Prius .:haha:

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I tend to get much better gas mileage than friends with better cars but I don't act like I'm in NASCAR either.

I wonder how much effect that will have on my truck's performance (when I finally get it back together).

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I get a consistent 10-11 mpg in my 72 C20 LWB with 350 v8 / TH350.

I have an Edelbrock 1406 600 CFM (this carb is supposed to be for better fuel economy)

I don't think it really matters much whether you have a v6 or v8 in these trucks.....they are rolling 40+ year old bricks! You really aren't going to get much better than around 10 mpg unless you change the transmission to an overdrive trans and put in a better rear gear....but even at that it won't be much better honestly.....with city driving at least.

It doesn't seem to matter how I drive, it's always around 10 mpg whether I drive like a granny or like a nascar driver LOL

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Before you start thinking about engine swap options, you have to weigh the cost of the swap installed ready to go, let me just ballpark a figure of 2k, just for the sake of having a number. Now that 2k motor nets you 18-20, and you're getting 10-11 now. Both engines STILL burn fuel, and your gas tank still holds the same amount, so in theory depending on driving time, it could take you a long time to justify the cost of a swap, just to save a couple bucks on gas. That being said, if your engine is tired and you're ready for a swap and prepared to put down money anyways....... LS that bad boy and be done with it!!!!!! :metal:

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x2

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something quick and easy you might try is putting some taller tires on the rear my dad always does that to get a higher gear ratio. I am sure there are calculators out there to help you figure it out.

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my 72 BB gets 200 miles per tank highway tops

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You forgot to mention this was on a trailer going downhill with a stiff breese pushing you.

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I wish I could get 10 percent of that, it would two times what I get now.

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This guy is totally right. A big mistake the uninformed buyer makes is trading off their current car for one with better mpg. It takes far too long to make one's money back.

That reason alone keeps me from getting rid of my 2002 Honda Accord. If I do my part, it will get 34 mpg on highway and 25 for city. My Civic (God rest its metal soul) got 50 mpg on highway and 32 in the city.

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not to get too far off topic but this is definitely the key.

I drove my 93 k1500 75 miles a day to and from work sure I only got 15/16 mpg but all that gas was about the same as a car payment! And sure the car would get double or better but that's only half what I was putting in the tank of the old girl!

Kinda like the hybrid argument an extra 4-5k for a hybrid buys a whole lotta gas!

Now on my 72 I need to at least go through my engine and if I start pricing things out it really wont cost me a whole lot more to do an LS so that's my plan just gotta pay a few more bills and hopefully by Christmas I ll have the front end off of her

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You know, I was just thinking....because I probably won't drive my truck very much even after I get it running again, that gear swap probably won't be worth it. I have a feeling the truck's gears will stay the same as those have been these 42 years.

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In my 71 lwb with 350, 3-speed, demon 625 4 barrel, MSD box, and 3.08 gears, I get 13 mpg pretty constantly. I have it 15 a couple of times but no constantly. I had an old man this morning tell me that his 80 pickup with a 250 and 3.73 gears only gets 8 and didn't understand how my truck got 13.

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Lefty, really said it the best, that the cost of the upgrade may never equal the savings. At the end of the day it is a pickup, designed to be loaded up and driven for a purpose. If its your daily driver, then the first thing to do is get a tune up, after that monitor your driving practices. Find routes that reduce the amount of stops, sometimes adding a mile may improve the mileage enough to justify the time. Takes a lot of fuel to move a brick. If this is not your daily driver, then drive it like you stole it, then when you blow it up, spend the money. Besides, i get 8 mpg, all day everyday, that's why it sits more than i drive it, but when i do drive it, i have fun.

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Had a different vehicle once that I used as a daily driver...56 miles to work, same on return.
It was a '69 Buick Riviera that had a fresh rebuild on a 430 Buick BB with a Rochester 4bbl.
That car consistantly ran 16-17mpg (all highway).
That thing was a lead anchor weight wise, but never let me down. Gas was $1.05 a gallon then.

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My '72 gets about the same, on the highway.

4.11 gears with turbo 350 trans. At 50 MPG, I'm already at 2500 RPM.

It's a blast in-town, but on the HWY, she's a screamer! Hoping to add a 2004R down the road and/or find someone locally that wants to trade out axles for 3.73.

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My 67 used to be a 250 straight six, 3spd, 3.73 rear. Back then it got 11mpg no matter what, city/highway/loaded/unloaded... didn't seem to matter.

It now has a 350/700R/3.73. Still gets 11-12mpg "city" but I can squeeze 15-16mpg out of it on the highway.

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You think 10 mpg is bad, I once owned a 3/4 ton Ford with a 390 engine that was such a gas hog that I couldn't even get the tank full if I left the engine running while trying to fill it up.

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I have a 71 longbed, 350/350 with 3.08 rear end and 31.5" tires which are about 10% taller than stock. I kept track of the mileage over 3 years and got 11.5 mpg using it as a driver, about 2500 miles per year.
Then I pulled the engine because it leaked oil. I re-sealed all the covers and intake manifold, painted it and put it back. No more leaks, but over the last 15 months it has averaged only 10 mpg. The only thing that I disturbed that might have some impact is the timing since I removed the distributor, but it is timed properly as far as I can tell, and certainly runs as well as ever.
Any ideas, other than global warming?

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Mine is a 72 long bed, 350 and 700r4 trans with 3.08 gears it gets me 15 mpg everyday with the occasional 16 mpg every now and then; but i have the TPI fuel injection system from a 1989 corvette (that was the donor for the engine and trans),

:metal: i guess the fuel injection system makes a difference.......

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I know my 52's and 53's all had taller tires in the rear. And my Dad's 65 also. It did make the speedometer off by a couple of mph. And, I think Your Dad is correct.

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my 72 Cheyenne Super LWB has a 350 4V TH350. I hauled some garbage to the dump and had it weighed before and after. With me and very little gas and empty, it was well over 4,000 lbs. I get 9-10 running around town. I thought that was pretty bad but was talking to buddy who has a newer Tundra. He says it gets the same 9-10 mpg. AND it was recalled to get the frame replaced!

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just to chime in, I'm gettin about 12 city and 17-19 hwy if my calculations are correct with a 350 and .308 in the rear withh a 700r4 on my 68 gmc stepside but after reading what everyone else is getting I'm not so sure anymore haha

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If gasoline prices were at least$ 2.50 a gallon, I'm sure that nobody will worry, by modifications we do is almost impossible to make our trucks have more performance. I already I convinced that my truck is like a toy for my. I have a 305, Rochester4 bbl, headers, 700r4 transmission, 3.42 rear end and yields only 11-12 per gallon.Last what I intend to do is: change to 350 engine, and 3.73 rear end ratio, and only because I want to convert it to rear disc brakes, hope to win another 2 miles.

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wouldnt 3.73s yield worse milage than 3.42?

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Good question for those who have 3.73 ratio.

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With the OD tranny I don't think the gear change will be a factor. going to more cubic inches probably would hurt more.

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A full size pickup of essentially any year is a HEAVY vehicle. These types of vehicles need adequate torque to move them around easily. The smaller the engine, the less easily they can move under their own power.Then theres the trade off between too many cubes with enough power and the opposite....

My point is that you can't cheap laws of physics and have both worlds. Modern technology fairly good MPG numbers in the newest pickups, and you'll read in a magazine where someone has a super sophisticated engine in an older pickup that gets 20+ MPG.

I rate a 250 six banger in the somewhat under powered class. possibly w/ some super tuning, fine adjustment and massaging of your carb, you might be able to get a little bit better MPG from your ride. What type of carb do you have now? What kind of a carb is that Holley???

If the engine is original, ring seal and such may be getting weaK. Have you ever performed a compression test?

11-1/2 MPG's is not a bad number, my opinion...

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Swapping out the 350 SBC w/ a Holley (poorly tuned), 465 trans and 4.10 Dana that's getting about 5-8 MPG for a 305 TPI, a 2.95/.63 T5 in the '69 GMC C2500. There's a good chance that mileage will be better. If it's not good enough, then I'll swap out the rear end gears for something more economical. This truck will get run around town and in the Foothills a bit. The '72 C10 Cheyenne (402/QJet/TH400) will get the LSx and OD automatic. That should improve the solid 10 MPG it's getting.

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It does sound high but then again my brother gets about that with his 305 v6. Granted he just drives it to school and back.

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I really think keeping the RPM low is the key to good MPG on the HWY. I've been driving my truck from San Angelo to Lubbock for the past six months. It's about 200 miles each way. At 65-70, I typically get 10-11 MPG on the HWY.

Motors is tuned very well. I've spent a great deal of time on timing and tuning. Carb (Edelbrock 1406) is tuned well, recently rebuilt. One thing I did notice was, the plugs that were in the motor were .35 gap AC Delco. I swapped those out for Bosch Split V's gapped at .45 and it ran much better. Not necessarily MPG, but just idled better and was a snap to tune to the motor.

Coming back from Lubbock yesterday afternoon, I decided to just take it easy and keep the truck at 55 MPH. At 55 MPH, I'm at around 2750 RPM. I normally drive at 65. Gas mileage was considerably better. I normally have to stop in a town about 45 miles from home to refill with 1/8th tank left. This time, I was able to make it all the way back on one tank. 13.8 MPG.

Really need to get an overdrive to drop the RPM down and be able to drive at reasonable speeds. The only good thing about driving that slow is, I never have to pass anyone!

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RPM at highway speed isn't the only factor affecting fuel economy. How much air you have to push is also significant. The Department of Energy estimates that an average family car will have a 17% fuel mileage penalty at 70 MPH vs mileage at 55 MPH, but that's for an average family car. A 67-72 Chevy/GMC truck is far less aerodynamic.

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Yet another mpg thread lol. 12mpg with a 250 is about what I used to average with a freshly rebuilt 250 in a 69c10 I used to own. It had 3.73's and 3ott. Best I ever got was 16.5 cruising at 60mph on flat ground with no wind. Im currently running a tired smog era 454 in my Burb and getting close to 12mpg on the highway with 8 in town. My take on it, like others have said, is a 250 is really underpowered in these trucks. A 350 will get as good or better mileage and be much funner to drive.
If you like to tinker you may be able to improve your mileage with a dialed in HEI. Add a electric or clutch style fan and build a cold air intake. Lots of idears on here for maximizing mpg. Just remember at the end of the day its still a heavy brick with aerodynamics akin to a Westinghouse and old technology. Mileage will only get so good.

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My dad had a 460 Ford-same thing-he only owned it for two months