I purchased my 86 F250 6.9 mainly for utility, but the recent (very bad) snow storms have required the use of the equipped 4wd in my truck. Anyway, all the recent use has interested me in what kind of mileage the truck gets. I do MOSTLY city driving and some highway driving. I usually only drive 55mph because my tach bounces around like a bunny rabbit on speed and I don't know the actual RPM of the engine... It sounds angry, so it gives me a reason to drive 55mph where others have told me is the optimal highway speed for efficiency... still I would say highway only accounts for 10% of my driving. I filled the truck up today, did some calculations and came to a conclusion of 21.1mpg average. I honestly about died because I have a 4 clyinder CAR that barely gets 21mpg in the city. I think the 6.9L diesel was built to last until the end of the world. I have got to say that I am totally hooked on Ford Diesels now. I can't wait for spring to roll around so I can do some cosmetic repair and build a flat bed!

 

thats pretty good, i have a 86 diesel with a banks kit, stock rear,4x4. I notice that when you drive over 55 it heavily decreases gas mileage. my truck runs about 2600-2700 about 75mph , maybe a little more! and it gets about 13mpg when i run it like that. If you baby it at 55 it will get 17-20 but it's all about your rpms. thats why the four speed manual sucks, a guy on ebay tolm me that you can swap all the diesel transmissions from the 6.9's to the 7.3's all the way up to till they put the speedocable onthe rear axle making it so you want to get the earlier trans. Does anyone know how much you need to madify driveshafts? cass

 

Or if you want more speed and easier installation is it easier to replace the gears in the rear?? I'm sure alot of people are wondering about this although the low gears that come from Ford are great for towing.

 

Many times I have thought the same thing. If this just had ONE more gear... even if the ratio wasn't much different than the 4th. Even if it only dropped highway rpm by 200... hell even 100rpm, I would be a happy man. The later transmission compatibility does not surprise me. It seems like Ford is a big fan of using designs as long as they possibly can. Engineering new parts and changing casting molds is HUGE $$$. Ford seems to entertain their designs as long as possible.

I would be interested in knowing the years of compatible tranmissions. I think my truck has about 330,000 on it.... engine starts right up in the dead of cold, but I think the transmission or clutch might be the first to go... If so I wouldn't mind sticking a 5 speed in there!

 

55 MPH is very good for MPGs, but 21 MPG is still very good for running around town. I got numbers like that on ocasion, but I am 90% freeway running. Recheck your MPG over the next few fillups to confirm your numbers, sounds like your doing good.

 

If you have a borg warner 4 speed which would be a t-19 behind a 6.9 you can put a t-18 or even a t-98 behind it. They all had the same bolt pattern for the flywheel housing and the input shaft was the same. They never offer any of those tranmissions with anything other then a direct road gear. 1 to 1 in fourth. There are alot of different ratios for first and second. There were ratios available that Ford never offered. There is a first gear that was available in curtain applications that went as low 9 something to 1. That is LOW. T-19's were 5 something to one and the 18's in the 70's were in the 6's. There are also exceptions. I haven't ever ran into a "diesel" or "gas" ratio. I haven't ever seen a pattern and I checked some old Ford bill of materials and they didn't show one for one and one for another. The guy I know at Ford said that it generally depended on the rear end ratio not the type of motor.

I had a 83 that had 307's in it and I got over 20 all the time. The motor was stock and in great shape. I had good pulling power over all with thopse gears. It sucked on a hill but it would have 355's also but in first it would still pull a mountain over. I still have the motor and it is in my 83 through 95 truck and it has a t-18 and 205 transfer case behind it now.


Keep in mind that you may want to look for trans. out of Fords. They were in other makes but they had differences. Not the bolting up to the motor but on the other end.

Also keep in mind if you want those tall gears that they won't fit in a Dana 60. You will need a Dana 61. That is why the 61 was built. I am pretty sure that 355's are the tallest gear that will fit in a Dana 60.

 

is it even possible to get/adapt a d61 for a front axle in a ford?????

 

NO. You will need to use a D40.

 

21 is the best my 6.9 gets, and im very proud of it for having 250000 miles on it!! 6.9 FOREVER!! i love that engine more then any other engine in fords!!

Ray

 

I get 15-17 mainly city with my 89 F350 dually with 4.10 gears 2x4 and a 5 speed. I couldn't be happier.

 

Do you mean D44?




16Vjohn, it you want annother gear, then you can convert to a 5 speed manual tranny, its been done on these trucks before. Prolly less work than a gear swap on both ends, and maybe cheaper.

 

what model is the 5 speed and do you hve to change your clutch at all? cause i like my external slave cylinder on my 4 speed!

Ray

 

There are definitely differences between a gas four-speed and a diesel unit. 2nd and 3rd gears are different ratios. I believe that second is higher and third is lower or vice-versa. I'm not entirely sure which right now. I know this for a fact because I bought a reman T-19 for my truck and immediately noticed a difference on the first road test. I'm looking for a Ranger Overdrive for it to deal with the issue. As to mileage I wasn't too disappointed on my trip from Ohio to Texas averaging about 8-9 running 75 for the most part. As to why the mileage doesn't bother me is simple my combined total weight was over 24000 pounds between the truck, trailer, and everything I had loaded also. Just my two cents.

 

There are definitely differences between a gas four-speed and a diesel unit. 2nd and 3rd gears are different ratios. I believe that second is higher and third is lower or vice-versa. I'm not entirely sure which right now. I know this for a fact because I bought a reman T-19 for my truck and immediately noticed a difference on the first road test. I'm looking for a Ranger Overdrive for it to deal with the issue. As to mileage I wasn't too disappointed on my trip from Ohio to Texas averaging about 8-9 running 75 for the most part. As to why the mileage doesn't bother me is simple my combined total weight was over 24000 pounds between the truck, trailer, and everything I had loaded also. Just my two cents.

 

Just filled up today and got a proud 13 mpg. Some might think that's terrible, but when you add in the fact that I lack an overdrive, 4.10 rear, N/A, and weigh close to 10k lbs.....13 mpg doesn't sound too bad after all!