Manual versus automatic mpg on 2WD D350

[888]

How many of you guys have manual tranny 2WD D350 trucks and what kind of mpg do you get?

I owned a 1992 manual tranny D250 2WD for 5 years and recently sold it due to getting to the point of no return rust wise. The best rust free replacement I could find was a 1993 D350 DRW automatic w/OD, I wanted the extended cab so that made the decision even easier to buy it.

The guy who owned the D350 told me he got some ridiculous mpg that was more than my D250 so I blew that off as being BS. However, I didn't expect the mpg to be as bad as it is, right around 15 to 16 on mostly country roads at 55 mpg. The 1992 D250 got maybe 22 to 25 on the same drive and I didn't expect that out of the D350.

However, years ago before I bought the 1992 D250 I had a non IC 1989 D250 2WD with the 727 3 speed automatic and it generally got 21 to 22 mpg so I thought the D350 being an auto with OD might get a little closer to 20 than 15. I don't know the rear axle ratio on the D250's but I know the D350 has a Dana 3.5 based on the options sticker under the hood.

I guess the root of my question is whether changing the D350 over to a 5 speed will get me much increase in the way of mpg. I remember now why I got rid of the 1989, I HATE driving automatics. I fell in love with the D350 and knew my chances of finding another one in similar condition were nil so I bought it and decided to try to live with the automatic. It's not going very well. I guess part of it is the amount of pressure required on the accelerator to keep the D350 moving, the D250 seemed to be a lot more responsive, yes I do realize the D350 weighs more. But also I just love shifting gears.

There is a place near me that does the swap and they keep the automatic stuff for resale. I know of another place I can get a full swap kit for $500 less, do it myself, and resell the automatic stuff to offset the cost.

I guess I can live with the automatic but I'm not going to enjoy driving it as much as I would with the manual. If I can increase the enjoyment and get some reasonable increase in mpg from the swap, then that makes it easier to think about swapping.

TIA for any information you can provide.

Joe

[Deathrod]

I think it's more that the non ic motors just get better mileage then the ic motors. Why? Could be injectors, lack of the resistance of intercooler.....somehow the smaller hc1 helps with mileage......I don't know why but seems non ic get the higher mpg. A manual tranny vs a stock 727 or 518 will always get a little better mpg, but how long would it take to recoup the cost? If your truck gets 15 with automatic I doubt it will be 20ish by just going to a manual.

Maybe someone who has done it could give their numbers on how much mpg really changed. In the end if you like banging through the gears, ditch the auto.

[CWT]

Maybe the big difference is the rear gear. I know my non ic 90 has the 3.07 rear end. makes a big difference.

[RCCUMMINS89]

All depends on how bad the auto is... I've seen where trucks have gained 5+mpg going to a manual.

I've personally never gotten any different mileage between a non i/c truck and an i/c truck, always been exactly the same. Any manual truck that I've owned...18-25 mpg (I've owned a lot of them), only auto truck I've owned was 14.... my dad had an auto truck, it got 14.5... his manual truck gets 18.5.


Edit - non i/c trucks do have more timing from the factory though... therefore should net better mpg on a bone stock truck. I don't exactly leave anything stock.

[888]

Maybe the big difference is the rear gear. I know my non ic 90 has the 3.07 rear end. makes a big difference.

Is it an auto or a manual? I suspect my manual 1992 had a 3.07 but never checked, don't know what the 89 auto had.

[888]

All depends on how bad the auto is... I've seen where trucks have gained 5+mpg going to a manual.

I've personally never gotten any different mileage between a non i/c truck and an i/c truck, always been exactly the same. Any manual truck that I've owned...18-25 mpg (I've owned a lot of them), only auto truck I've owned was 14.... my dad had an auto truck, it got 14.5... his manual truck gets 18.5.


Edit - non i/c trucks do have more timing from the factory though... therefore should net better mpg on a bone stock truck. I don't exactly leave anything stock.

What do you mean by a bad automatic? It's the usual auto/OD (A 518?) best I can tell, has a good sized tranny cooler underneath behind the drivers side door. Fluid looks good and it shifts well, only thing I can see that seems at all sketchy is it changes gears with authority when going from park to reverse or reverse to drive, for example.

Right now, it's set to shift into OD at around 35 to 40 mph depending on how hard I'm on it. The harder I'm on it, the higher the revs and the smoother it seems to shift. It will get up and go with no problem if I get on it, considering the size and weight of the truck. It's just not a manual.

[RCCUMMINS89]

By how worn out the converter is... etc...

All 5 speeds received 3.54 or 4.10... However, one may have been special ordered.

[CWT]

Yes mine is auto.

[oldestof11]

Adjust your bands. I gained a solid 1mpg from that alone.

My theory of smoother shifts with higher RPMs is because you are way out of the torque range. Mine kinda glides into the next shift when the RPMs are way up there. However when I roll into the throttle and the RPMs are lower while being in the ideal torque range, it shifts nice and firm.

[CAJUN 93]

on a run from La to Ky for the 1st gen get together my truck (93 d350 getrag 3.54) and member TomTom's truck (d250 auto 3.54) with the cruise set at 68 mph unloaded running together got IDENTICAL mileage. We stopped at the Love's truck stop just east of Meridian MS and topped off and ran all the way into Kentucky non-stop. My truck got 22.8 and his got 22.7 calculated with pen to paper. I know around town the stick in mine is good for about 1.5 better than the built 518 in the wife's but the interstate evens that right out.

Daryl

[1STGENFARMBOY]

a tail wind or head wind makes a huge difference in my truck.

[CWT]

^ seriously?

[PToombs]

Yup, I agree with Dar. A headwind will knock the snot out of the mileage, same as driving 75 vs 65. After all, we are driving a box.

[CumminsPower59]

When I converted my W350 from a 727 to a NV4500, it gained a good 4+ mpg (14 to 18-19). I still run direct (fourth) most of the time, runs 1700-1800 rpm @ highway speeds. Since the conversions, best mpg I've seen was 20.9 last summer. The 727 was really loose, and took quite a bit of throttle to do anything. My pile is lifted a little, and those 3.07's are spinning 35" tires...so I'm pretty happy with the mileage it's getting.

Apples to oranges, but something to chew on.

[888]

Adjust your bands. I gained a solid 1mpg from that alone.

I'm a 3 pedal person so I honestly have no experience with this. Can you point me to a link to help with this? I have a factory manual set but it's from my 89, that had the 727 so I'm not sure it would apply and don't want to assume.

Thanks