Hey everybody, I'm basically here to complain about my mileage. I have a 1985 F250 HD 4X4 With a 351Windsor. I believe it has the C6. I got absolutely atrocious mileage on a recent weekend away. Something like 7-8 mpg. 120-140 miles cost me like 100 bucks. Basically I'm super pissed off that I cant drive faster than 90kms (50-55miles) an hour or I get 7mpg. Engine is running good and tranny shifts nice and smooth and doesn't slip. The truck is a big one. Extended cab long box. I got this truck from my uncle for free because I was stupid and wanted it. It's completely overkill for what I do. I don't use it to tow or haul anything. I basically use it to go places with mountain bikes and had planned to get a dirtbike. I wanted to go on roadtrips and go snowboarding backcountry with it but 7mpg is unacceptable. Basically I've got 5000 into it and it's getting a new steering box tomorrow. I can't deal with this mileage, I would like some advice on whether to tranny swap it to one with overdrive, (manual or automatic) and how much that costs/ how difficult it is/ how long it'll take. I'm an autobody apprentice and am fairly mechanically inclined but prefer the easiest method. Could take truck to my uncles house and build it there. Might also sell the truck for around 4 grand and get something smaller. Looks really really good, it's on my profile. 150,000 miles.
Anyway thanks for reading my rant, any help or advice would be appreciated.

 

I have an 85 XLT Bronco. $200 for a set of lock out hubs and a custom tune on the aftermarket carb and the best i get at 50 MPH is 9 MPG. I am in the processes of getting together everything to change to a ZF5. The C6 is indestructible. But it needs another gear for sure. I love my Bronk. But can hardly afford to drive her. And yet it is my town car for the family. It's got to get better than this. Maybe a diesel?

 

Managed to go 240 kms for 70 bucks once. Working out to roughly 10-12 Mpg.
But I didn't go faster than 85 kms an hour and feathered the throttle. The speeds I have to travel to get 10-12mpg, which is ****ty are so slow! A 400 km trip takes me an extra hour and a half in this truck because I can't go 110kms an hour, which isn't even fast. It's regular cruising speed. . .

 

What gears does it have in the axles? If you've got something low like 4.11s in it then you might look at a gear swap to something that's better for highway driving.

Also check out the emissions system and the ignition. For example, on the mid 80s trucks like yours, some had ignition systems (I think they're called EEC-IV) that would lock your timing to a preset setting if you replace the stock carb with something else (these stock carbs were sort of electronic). All the stock stuff can communicate and function, but when stuff gets changed, then it doesn't have a clue what's going on. lol

 

I looked it up in my manual and it's a 3.5 something? I think it was a weird number like 3.52.
Considering that it costs 200 bucks to fill I want to get 5-700 miles out of the two tanks.

Oh I forgot to mention, this truck is bone stock original 2 Barrel and passed an emissions test. It has ever so
slightly leaky valve seals. The problem is going down the highway at a constant speed with the engine
screaming away. The truck has no tach.

 

That isn't too bad. You look like you're running stock tires in the pics you've posted on your profile so that's not gonna be your problem. (I've seen a guy on here once say he wanted massive tires on his little 2.5L Wrangler and in the same sentence said he wanted gas mileage... )

I think you should start looking under the hood and figure out what you're working with if you haven't already.

 

What do you mean what I'm working with? The engine runs great. It's the gearing I'm pissed at. The engine ****ing roars down the highway at 110-120 kms and gets unacceptable mileage. I want advice on different transmission options. The truck is bone stock in really good shape with no mods. Stock everything. How am I supposed to afford highway cruising if I get 12mpg at 45 miles an hour! It get progressively worse the faster I go

 

You have something badly wrong. Here are a few of my experiences, all with 3.50 gears and running 62 on the highway.

• 1982 F150 351W with a 2bbl & a C6 Got 13.5
• 1981 F150 4x4, stock 351M 2bbl and C6 got 10.5
• 1981 F150 4x4 with a built 351M and NP435 got 14.25
• 1981 F150 4x4 with built 351M and ZF5 gets 15.0 and I expect to get close to 16 before it is over

Your F250 isn't heavy enough to make a significant difference vs an F150, and all those are standard cab and long beds. So, you have a problem or are running huge tires you haven't told us about. I would check that the choke is coming fully off. Then do a leak-down test. Check your timing to ensure it is set correctly and is advancing properly. Again, something is badly wrong or you have cards you aren't showing.

 

Ok. I Have bone stock everything like I said. 31 Inch tires. Fairly small narrow tires. I don't know **** about engines. Anyway I went from Vancouver to Seattle. To Bremerton across the ferry. Then back home. Drained the tank to empty after adding a 2.5 gallon Jerry can then made it to the gas station beside the border. It was 441(274miles) Kms and The truck needed 25 Gallons - the 2.5 jerry can. Well anyway after doing the math it appears I'm a tool and it gets 10mpg. Still not very good! Anyway I cruised at 70 miles and hour or so. Running 40psi in all four of my P265/75/R16s. What numbers would overdrive get me. Maybe 40% more?

Anyway, I don't know where the choke is. All I know is that it makes **** run rich while cold? I'm a body guy lol. Rust and paint is what I know + really basic stuff like doing brake work. My experience is entirely bodywork!

 

Drop yer tires to about 30. Or 32 as is on yer door tag. That will gain a couple easy.

 

They bulge at 40 though. The truck is about 5500lbs with me in it

 

Something is definitely wrong. I would do a CONSTANT 9-10mpg with my 80 F350 4:10s 429 C6 and 35" super swampers and that was full throttle, doing burnouts EVERYWHERE.

Do a FULL tune up(cap,rotor, plugs, wires, fuel filter, air filter). Also like someone else said, make sure the choke is coming off all the way. Keep your tries aired up as much as you can take the ride. make sure none of the brakes are dragging. Also slow accelerations help as well. You should be able to get 12mpg

 

The harder the tire, meaning the more air pressure they have, the less resistance. That's why trains get such good efficiency ratings - steel wheels don't flex much and, therefore, roll easily. So, if you can stand the ride at 40 psi leave it there.

Getting 10 MPG at 70 MPH isn't bad. These trucks are basically bricks or barn doors with respect to aerodynamics. I'm told that Ford spent a fortune in the wind tunnel on them, but I think they were just confirming that the designers got the instructions right - make them just like a brick. So, running at 70 will certainly reduce your MPG.

No, overdrive will not get you a 40% improvement. The last two trucks I listed are essentially the same truck, and the difference is going from the NP435, which is a manual tranny with no OD, to the ZF5, which is a manual tranny with OD. So, my RPM at 62 went down from 2700 to 2100. And my MPG went from 14.25 to 15. Yes, I expect to get a bit more than that by tuning the carb, but if you don't know anything about a choke you won't be tuning a carb.

Speaking of the choke, you will find it under the air cleaner. Pull the air cleaner when the engine is hot. There is a valve or butterfly at the top of the carb that should be completely open with the engine hot. If not, you need to adjust it. But, we need to know more about your engine to describe how to adjust it. I believe you have a 351HO, which has a 4bbl Holley-built Autolite-designed carb called a 4180. The Holley has a power valve in it that is known to fail and cause the engine to run very rich, which will absolutely murder your mileage. But, again, if you don't know about a choke you won't be pulling the power valve, and will have to hire that work done or be willing to learn. And, there's the question of ignition timing, but that would require a timing light and learning as well.

In any event, an 85 351W/C6/3.50 geared/31" tired truck should get around 12 MPG in my guestimation if tuned properly. So, are you interested in learning how to fix it? Or, are you willing to shell out some bucks to have it fixed? It can be a bit expensive to just take it somewhere and say "fix it" w/o knowing what the problem is. But, at 10 MPG you do have some problem as you probably should be getting 12 when running at 70 and more like 13+ when running at 60 - 65.

 

I agree with gary. My 460 with a poor tuned carb 285/75/16s 3.55 gears and a c6 gets 8-12 mpg. You have issues deeper then needin more gears. Just listen to the advice given and you will be impressed.

 

Ok. To be quite honest. I live in the city and have no place to work on the truck really and I'm quite poor from buying autobody tools. There's a mechanic shop right next to me and they seem to be giving me a good deal but I don't know.
They're installing a steering box for 200 and would install valve seals for 200. Anyway my mechanic friend said I had the 2 Barrel. I'll post my exhaust readings later if that would help you guys help me. Truck has new brakes/ no dragging. I'm willing to do work if it saves me money but keep in mind I know literally nothing about how to work on engines. I change oil and that's it. The truck had been sitting for a long time by the way.