The Stovebolt Site Forums The Shop Area Engine Shop 235 fuel milage

Curious what kinda milage folks get with these engines?
As a kid I remember it was pretty good when they were running right.

Not too bad but not as good as you would think. With mine, around 12mpg to 16 with the O/D and maybe a little bit less with the hydromatic.
dg

Wow I think my 460 F250 does that good, are you sure???
I plan on doing a fuel economy 235 for my truck. And if the plan works its going to be better than 12 to 16, at least I hope so.

Um, Er, I hate to [censored] people off, so don't be offended but I get minimum 23/24 mpg with my cranky old 235 and on long trips do as well as 28 doing 56-60 mph.I run 10W/30 syn. oil, I run the valve clearance .006/.018, I have a 3.91 rear and a Chevrolet built 3 spd..I run syn. lube in the trans. and rearend. My tires are at 30lbs. C'Mon people, its a 135 horse 6Cyl., 115 if you're lucky to have the "economy" version.If you're getting less than 22mpg,you-and your truck-have serious issues. At 3.50 a gallon, I'd start to address them, real quick.

I got 18 mpg with a 235 and a 261 at 55 mph on the highway (3.90 rear end) and the same 18 mph at 60-65 mph with a 3.55 rear end.

When I run at 65-70 mph, I get about 12 mpg.

My speedometer has been calibrated to the actual distance traveled at 60 mph. It would have been off by about 10% due to the larger diameter of the radial tires and about and 10% due to the 3.55 conversion.

I am neither [censored] nor offended by reading 28 mph (above) at 56-60 mph - I am impressed and astounded.

Let me repeat that, Um, Er, I hate to [censored] people off, so don't be offended but……………I think anyone that believes that they are getting better then 17 or 18 miles pre gallon of gas MAX with a 235 or a 216 Stovebolt Six needs to review his or her math skills.

Fuel mileage has ALWAYS been at the top of the list when it comes to selling hype. GM would have posted the highest ratings they could have to sell more vehicles. And the hundreds of engineers that spent litterally hundreds of thousands of hours developing and testing the Stovebolt six would have maximized every means to get the most out of these engines and still have them last for 60 or 70,000 miles.

The Chevrolet Truck Data Books for Chevrolet Salesmen has a section in the back called “Certified Performance Proofs” where they present numerous examples of the fuel performance based on actual usage. The absolute tops that any of the light trucks reported is 18.05mpg with the average being 15.15 mpg.

After having my stock 1950, 3600 216, w/4sp and a 4.10 gear for about five years and keeping very meticulous records of the mileage and tuning touch-ups about every 500 miles my averages run between 14 to 15 mpg. The engine has 50k miles on it, my compression is within the factory specs, I did do a valve job on the engine when I brought it home because of a burnt exhaust valve. The oil scrapers were worn some so I did have to add oil periodically between oil changes.

Since the entire drive line has been rebuilt and the top end of the engine is back to snuff, the only thing left is the bottom end. So last fall as the bad weather set in I sent the short block out to be completely rebuilt. This year the entire running gear of the truck will be factory fresh from the tires that touch the ground right back up to the carburetor where it all starts. What am I expecting to get for fuel mileage with the entire mechanical portion of the truck in new condition??? Realistically I’m expecting between 15-17 mpg on the hi-way unloaded and 14 -15 mpg around town. So that’s been my experience and I’ve got the log book to back it up for the last 8,000 miles.

As far as the fuel mileage increase by being able to travel at 65-75 mph, these old trucks are not of the most aerodynamic shape and they create a LOT of drag. Energy required per unit distance is roughly proportional to the square of speed when you talking about air resistance. Parasitic drag is subject to the inverse square law and it takes a good amount of throttle to maintain enough power at those speeds, which translates to poorer fuel economy. It’s indisputable that you will get the best fuel mileage with any vehicle at between 25-35 mph simply because of the drag that has to be overcome at higher speeds.
A 3.90 or 3.55 gear will increase your mileage if you drive at a steady 35 mph but not if your running the express way at 75 or 80 or if your in stop and go city traffic.

So in my opinion if your buying an old six cylinder Chevy expecting to get the same fuel economy as a new high-compression, overhead cam, fuel injected, computer controlled all aluminum (read light) engine, then I believe you will be somewhat disappointed.
Denny Graham
Sandwich, IL

My 75K miles 216 gets 15 mpg most, 3:08 rear,
T5 Trans

i agree with you denny. i keep very accurate records on all three of my trucks. even though two of them are rated for 16000 gvw and my 40 is a 250. the best i can get on the big ones are around 8-11 and 11.5 to 12.5 on the 40. top speeds for me is 53 mph that i run. im not dissappointed because i realize the dynamics but im always striving for that little bit more and havent found it not to say there isnt anymore to get.

Yup, about as aerodynamic as a cinder block!
I get maybe 12-14, if I keep my size 14 out of it. Haven't really checked what my highway mileage is, I've only taken one long distance trip in (Danville, IL to Greenwood, IN), and really couldn't get an accurate reading as I spent too much time trying to find the place I was going due to faulty Mapquest directions. I'll take a guess and say it isn't any higher than 16-18, tops.
BTW, for those not familar with mine, it's a '55 2nd, 235 with dual Holleys, Fentons, an overdrive 3 speed, stock 3.90 rear gear, and 30" radials all around.

I think someone is confusing engine size and power rating with engine efficency. A 216/235/261 has to be one of the most terible designs ever as far as efficency is concerned. Low compression, long log type manifolds with both individual and siamesed ports, runs at a low temperature, heavy recipricating parts and valve train, oil drain back falls onto moving parts, temperature gradient varies widely from front to rear, plug location and chamber design not the best for flame propagation, and I'm sure points that others can bring up. darn, I love them but will NEVER see the day they deliver 25+ economy with any gearing or tire size known to man.

Well its a I6 so it is efficent just saying that. Good ballanced engine. They ran log intakes till the late 80's, so they had to be ok some were. Good set of gears and a light foot I could see 23 MPG. Mine runs at 180. Thats a good temp. New cars have to run at 200 to help with all the egr crud. Not the best I6 ever but it aint the worst.

Sorry inline 6 fan.

Here is a possible 25mpg 235; 12 port cross flow head with electronic port injectors and tuned individual stack at each intake. Tri-Y headers with equal length tubes and anti reversion flanges. Computer controlled igniton and air/fuel with knock and O2 sensor, 500 gram pistons/pins with weight shaved from the crank to compensate, roller cam with hollow lifters and needle bearing rockers, coolant into block at each freeze plug hole and exit at both the front and center of head, high pressure radiator and cap running at 230 degrees, synthetic lube all around and tall narrow radial tires running 40-45 psi. Now, get rid of those wipers, door handles, antenna, and loover the tailgate and it's ready for an economy run.

My 55.1 3100 with a 235 and OD has gotten about 13 mpg in the 3200 miles I've driven it. A combo of in town and highway. I'd be ecstatic if I got 15 on the highway at 65 mph.

For comparison I trailered it down to Austin for the Lone Star Roundup this last weekend. I got 14.5 mpg with my Ram/Cummins tow rig. So over the 500 mile round trip, it cost me about $30 more in fuel to tow the 55 down and have 2 vehicles in town than it would to have just driven the 55 alone.

At the show a teenager asked me what kind of mileage I got from the 55. I told him that about the best I'd expect was 15. I explained that the engine design was about 50 years old, and everything the industry had learned about fuel economy had happened after its was designed.

regards,
Leon

I have the 2 ton firetruck with the two speed real axle so I get 10 to 11 mpg... But what would you expect from a truck with that rear axle and weighs 9,640 lbs? It isn't my motor that sucks down the fuel...

Love it but hate the fuel costs! I'll still drive it when gas reaches $10 a gallon!