Transmission/Fuel Economy?

[Aryeh Levy]

STILL waiting from www.truckperformance.com (http://www.truckperformance.com) for my oil filter relocation adapter. Sigh...

Took my truck to AAMCO for a flush - they looked at the fluid - it smelled burnt to me. Said they should evaluate it.

I've been driving a 1998 3500 Dually Auto. I get 12-13 Mpg. I'd really need to get 17 mpg.

Would a transmission rebuild help here? Or are my 130,000 Mile injectors causing it? Has anybody gotten 16MPG+ from the factory on the 1997 1998 or 1999 3500 duallys? or is 13 from the factory normal?

How can i do better?

No Manual Tranny Responses Please.

I've gotten 12-13 since i got it. Changd to a K&N
filter - Helped with spool up noise (nice whine) no mpg really... Got kennedy's boose fooler - much more boost, no more smoke on hard accel (got Kennedy's pmd relocator, with #9 resistor) - nice gain in power, slight gain in mpg i think...

I read a buncha months ago somebody said the Mechanical turbo master gained them 5 mpg!! Anybody else verify those numbers? Can the mechanical wastegate spring make efficiency more?

[ace58]

Anything is possible however, generally speaking, 13 is between 20-25% better mileage than a comparably equipped gas 6 wheeler the same age.

That said, I don't think your transmission is the answer. The extra wheels, weight and gearing of your dually are the culprit.

My 1999 Suburban gets 16 in everyday use with 342s whereas the gas with a 350 averages 12. Same percentage applies.

[jdmetcalf57]

My truck was like yours a 99 k3500. I was getting the kind of mileage you where. It was very dissapointing. I changed gears and put on larger tires, put on large exhaust no cat. This got me 1-2 mpg. Best thing I ever done was get rid of the duals and change from an auto trans to a manual transmision. I now get 15+mpg pulling my camper and somewhere about 18-20 empty. I am going to get well over 500 miles on my current tank and have pulled my camper about half of the time.

Unless you haul an extremely heavy load you don't need the duals anyway just use load range e tires. As a bonus the truck rides better now. I now like my truck where I was ready to trade it before.

I don't tow a 5th wheel, it is a high low type camper but before the trans change and change to SRW I was lucky to get 11-13 mpg. Along with the 4000 lb camper I usually have 2-3000lb of gear in the back of the truck.

[KerrySchrantz]

I'm driving a 97 dually. I get around 14.3 around town and between 17.2 and 17.8 on the highway. The only mods done are 238/85/16 tires and a 3" exhaust from the cat back and Kennedy's boost module. I will tell you that driving habits play a BIG role in mpg's. I had to get home in a hurry from Florida once and kept the truck right at 85. Big mistake! MPG's came in right under 14 (although I did get home 2 hours early)

[DA BIG ONE]

Mods for tranny require deep pockets, 3 disk clutch in billet torque converter, kevlar clutches, permium steels, cyro treated hard parts, & programs cost will far outweigh any gains unless truck can bring some kind of meaningful return in money making department.

As for mpg the spread between fuel costs of gas & diesel is far and now backwards, so any gains for the average joe w/diesel will be taken away by fuel costs!

[Dvldog 8793]

Howdy
RPM, rolling resistance, progressive wind resistance and static load are what determine the differences in like vehicle/engine MPGs.
If you want 16MPG, lose the duals, change to 3.42, get your truck as low as you can and get ride of any wind snaggers(visors, brush guards, big lights ect...) And to top it all off drive nice(that's the hardest part)
Do all that and Ibet you'll get better than 16MPG.
L8r
Conley

[JoeyD]

Are you still running the stock size 215 tires? That with the 4.10 gears and the dual wheels will give you low mpgs.
The mechanical boost controll will not get you much if any better milage.

[GMCfourX4]

Along with everything said here, I will disagree slightly with JoeyD on the mechanical boost controller. Depending on how your ECM controls boost (it isn't the same from one truck to the next) and what speeds/RPMs you drive at, you could get better mileage with the mechanical controller. My ECM would leave my truck with 0-1psi of boost on the highway under most driving conditions (except steep hills, heavy throttle, etc...). The mechanical controller will usually give between 3-7psi, depending on how its set, and the cruise speed. You do have to watch out how you set it though (trial and error) b/c if its too high, the additional backpressure on the exhaust side will outweigh the benefits of the boost.

-Chris

[Aryeh Levy]

Kerry Schrantz - Do you have an automatic tranny???

I've got 245 tires

I think the speedometer is correct - it's right on with the radar gun screens. I guess i should check with GPS.

Exhaust mod is coming after my replacement of oil filter and cooler lines. Thinking of running a whole tank without anything but a 3" downpipe - and earplugs!!! to see what a freeflow exhaust would get me

[RT]

How about looking at it this way:
You say you need to get 17mpg but what will this cost you? Do you know what your fuel costs are now?

For example:
25K mileage per year at 12mpg assuming $2.75/gallon = $5729 yearly fuel costs

25K milsage per year at 17mpg assuming $2.75/gallon = $4044 yearly fuel costs

So the difference is $1685 in this scenario. You could spend this amount on modifications and if it resulted in 17mpg then it would pay for itself in a year. After that you start saving money. It all depends on how much you drive. If you only drive 8-10K/year then the difference in fuel costs is much smaller and the payoff for mods will take longer. If you drive more the opposite is true. IMHO fresh injectors make a difference in mpg but in your case how much is questionable. I think if you really don't need the dually sell it and find a SRW 2500 with a 5speed and 3.42's. Mine averages 18.79mpg over a year combined city/highway/occasional towing. I have seen 20.5mpg on the highway with the CC set at 70mph. I think your truck is simply too large and heavy to deliver 17mpg without mods that would negate the true nature of a dually which is pulling stuff. RT

[Aryeh Levy]

Kerry Schrantz - Do you have an automatic tranny???

I've got 245 tires

I think the speedometer is correct - it's right on with the radar gun screens. I guess i should check with GPS.

Exhaust mod is coming after my replacement of oil filter and cooler lines. Thinking of running a whole tank without anything but a 3" downpipe - and earplugs!!! to see what a freeflow exhaust would get me

[KerrySchrantz]

Yeah it's an auto. Correction on above post the tires are 235/85/16

[ogrice]

I'm with jdmetcalf on this one. My dually has 3.73's and stock tires. With all the mods on my truck I see 18-21 unloaded and 16+ towing around 4k lbs with a high of over 18 mpg towing w/ propane over a 1200 trip. I personally have never owned and automatic trans vehicle till I bought my friends 65' mustang coupe.
If I can, I'm going to throw a TKO 5spd in that one too. Hoooooray for the three pedal drivers out there!!

I don't see 6.0l& 7.3l PSD or the 5.9 ISB owners throwing around those mpg numbers. HaahaahahaaHaaH!!!!!