I'm looking at a 1984 F-250 4x4 4 speed 6.9 diesel, very good mechanical condition. My 1977 is getting to be to nice to use as a truck. lol. So I'm looking for something that I don't mind getting a scratch in and that I can drive in the snow and haul and tow with. I'm looking for something cheap and this fits all of the above. My 77 is only a half ton and gets 7-9mpg. I know a lot of diesels get some pretty remarkable mileage but for some reason I don't think this will be all that good. My dad has a 1991 Ram cummins 2500 4x4 5 speed and gets 24 on the highway or around 20 average. What can I expect out of a 6.9? 10? 12? Or will it be up around the Ram? I have no idea.

 

I'm getting about 14-16 around town and the best I got on the highway was almost 21.5. Keep in mind that was unloaded at 55mph.

 

Wow. Thats awesome. Thats a lot better than I thought. I guess I maybe thought the lack of Turbo would hurt the mileage.
What are other people getting or is this the norm?

 

Many factors influence fuel mileage. This engine is capable of 20 mpg in the old days with the old style fuel. The new low sulfur fuel is dropping everyone's mileage, even your Dad has probably found this out if he has compared the mileage of the old fuel to the new.

4x4 will hurt mileage some.

Large tires will hurt the mileage

Lift will hurt mileage.

Type of tranny will hurt mileage

Gear ratio will hurt mileage.

The best scenario for the 6.9 is a 2wd truck with original skinny tires, no dually, and a 87 model with a 5 speed overdrive and 3.55 gears. Most of these came with a c6 or a 4 speed manual.

My truck is a good example. 7.3 diesel with a 4 inch lift, 35x12.5 inch tires, 4x4, 4.10 gears, 8ft bed regular cab. When it had the c6, the best I could get was 12mpg. With everything being the same, I changed the tranny to a zf 5 speed, and now unloaded I get 15mpg.

 

Yes my dad has mentioned a mileage drop. I'd say it has stock-ish tires, no lift. Pretty close to a stock truck, its a one owner with under 100k. I'm not sure on the gears. 4 speed manual trans.
So it sounds like mid to upper teens would be a good estimation, which is much better than I would have guessed, 15 would be great in my opinion.
Here's pics.

 

My brothers 6.9 with an automatic gets about 14 city and 18 highway stock with 33 inch tires. The engine is reliable as all hell and will get you anywhere but do not expect to get there fast.

 

I know this is kind of a noob ----okay this is a total noob questiuon but are diesels hard to work on??? I mean like compared to a gasser? And I imagine the old idi's are probably the easiest diesels to work on..??...?

 

I didn't much about diesels till I got mine about 4 years ago. Lots of reading in the idi forum and on the web has taught me alot.

The idi is a mechanically injected engine, so it's as simple as it gets. The powerstrokes make more power, but they have a computer with lots of wires.

The biggest thing you will find right away is these engines are heavy and are heavily built. They already come with 4 bolt mains, roller camshafts, and by nature a diesel engine has to have a thick strong block. These engines are known to run easily over 200,000 miles without a rebuild.

But they have their quirks. The biggest one is starting, and the systems they use to get them started. Starting problems are why most of them are sold. They have a fuel system that needs to be in top shape to keep fuel delivered to the injection pump, and they have a glowplug system that needs to be kept in good shape for reliable starting. It doesn't help that every parts store in the country will sell you unreliable glowplugs that will burn out in a very short time. If you get the correct glowplugs and do a little maintenance on the fuel system, they are a good engine. I really like mine.

 

All that is good to know too, thanks!

 

My 86 reg cab 4x4 6.9 4speed 6" lift and 35" tires gets 14-15 around town and 15-17 on the highway at 65mph. As stated above. do not expect to get there fast, these engines are slower than molassis in jan. If you hook a trailer to it they even get slower, if even possible

 

my dad has an 84 with a 6.9, 4 speed, 4.10's in good shape but all stock, it usually manages about 14 on average, but its usually working. for daily driving stuff it does around 16.

 

would anybody happen to know the stock hp/tq numbers for a 6.9???

 

I found this forum which should do the trick https://www.ford-trucks.com/forums/5...-9l-specs.html
It say their specs for the 6.9 is 175 HP - Torque 318 ft. lb

 

Wow. My dads 1991 Ram Cummins turbo diesel is only 160 horse. Something seems odd there.

 

It probably not a turbo diesel then, just like the early fords the cummins was also naturally aspirated in the early days, it didnt make much HP but the upside is that also meant it didn't use much fuel.