Gas Mileage is poor

[data89]

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?

[CST10]

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

[68shortwide]

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

[In The Ten Ring]

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.

[truckster]

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.

[Ironhorse]

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.

[Grumpy old man]

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

[In The Ten Ring]

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).

[1972BlueC20]

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

[leftybass209]

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!!!!!!

[88lsiroc]

Originally Posted by leftybass209

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!!!!!!

x2

[Nitis]

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.

[ho70]

my 72 BB gets 200 miles per tank highway tops

[Blue GMC]

Originally Posted by ho70

my 72 BB gets 200 mpg highway tops

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

[big mike71]

Originally Posted by ho70

my 72 BB gets 200 mpg highway tops

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

[In The Ten Ring]

Originally Posted by leftybass209

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!!!!!!

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.

[Nitis]

Originally Posted by In The Ten Ring

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.

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

[In The Ten Ring]

Originally Posted by Nitis

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

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.

[DreamRyder1963]

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.

[my67c20]

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.

[alsriv2]

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.

[BruthaMan]

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.

[67ChevyRedneck]

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.

[Eddie H.]

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.

[48richard]

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?