Engine/Transmission (1994 - 1998) average mpg?

[Ahopper]

Don/TX: i think i am going to try a new filter. or put the stock one back in to see if i see a difference at all.

DieselDoghouse: with your 4. 11s what are you seeing for rps at 70? do you know? i would have thought with 4. 11s your gas millage would have dropped because i would think you are running higher rpms? someone please correct me if im wrong b/c im not the best at this math stuph

 

[DonTX]

In discussions with Winter Texans down here, many of which have similar rigs as mine, the agreement seems to be that the 4:11s definitely suck down more fuel running empty than the 3:54s do for sure, but when loaded with a 12,000 lb 5th wheel, they often maintain they have a slight edge. We are talking old fogeys that almost all have automatics of course, most of which have never driven anything bigger than a Honda, and only to work. I personally maintain that IF one uses the OD and gearing of the automatic 3:54 equipped truck to its fullest, I can outdo any other combination (I have a background trucking my own big stuff coast to coast). I just have not had the opportunity to do a side by side comparison with one.

I maintain that keeping the rpms as near at peak torque as possible is the secret. Peak torque on my 97 is just a shade under 1500 rpm, so screaming along at 2k or better just wastes fuel.

I just bought a fifth wheel, will be doing some over the road research on pulling 11k this summer.

 

[HEMI®Dart]

I hit 20. 76 MPG this winter w/ OEM 245/75R16's, fanless & winter blend diesel. 3:54 rear. See mods in sig.

 

[GMichaels]

15 -16 mpg

Have a 97 3500, 4x4, 4:10, 5spd, 10 plate and get 15 tops 17 mpg unloaded, and 13 to 14 towing 13k. Guess with gas prices wish I had the 3:54, old truck got 22 mpg

 

[J.BURCHFIELD]

When I go 100 miles by the mile markers I see that due to larger tires my odometer says 96. A 4 mile difference so I figure 4%. When I check fuel milage I take milage shown and multiply (on my calculator) by 1. 04. If for example I had gone 400 miles the calculator would show 416 and I would then divide by gallons. If I had used 24 gal, it would come out 17. 33 MPG. A mixture of city and highway driving is usually slightly below 18 MPG. It is a 98 12v with 106K. Marine injectors, AFE Air filter and full synthetic in the crank case. Towing 4 to 5k costs 3 MPG. Before the Marine injectors towing cost 5 to 6 MPG. It baffles me how bigger injectors can increase milage towing but make no difference not towing. I use my Gear Vendor towing or not towing. The Gear vendor did not change the milage and when I went from 4:10 ring and pinion to 3:55 it made no difference. Not a complaint. Running at a lower RPM is nice and quiet and puts less wear on the engine. The engine will no doubt out last me. I do have a 4" exhaust and a see through muffler. I noticed with the 4" exhaust I can hear the turbo "whine" when I romp on it. Every thing you do makes a small deference and all together it adds up.

 

[dieselshadow]

My truck is so efficient, it actually makes fuel while driving:-laf

 

[J.BURCHFIELD]

A Gallon Saved Is A Gallon Earned.

 

[PSInt]

I feel your pain... . I only get about 13 with my 96

 

[DonTX]

My truck is so efficient, it actually makes fuel while driving:-laf

Mine did that too, I put on two of them gizmo thingamajiggers that were guaranteed to give me 60% improvement in economy, got tired of draining out the surplus all the time.

(OK, I AM from Texas, and we DO tend to brag a little bit sometimes)

 

[surfbeetle]

24. 7 mpg at 72 mph cruise control set. I drove from Sacramento last year to San Diego on one tank of fuel and drove another week on it. I got 722 miles on 29 gallons. That was after the larger exhaust, K&N, TST, new 354 gears and I am running 265's. I had the speedo gear changed by the shop that did the rear end. They said that it was 1 mph off with the tires. When I got the truck new, it had 245s and 410 rear end. It would get 18-20.

 

[J.BURCHFIELD]

I got it figured out. When you go somewhere with a tail wind you get great milage. Everywhere I go I have a head wind.

 

[MMcCallie]

Driving from St. Louis to Denver i just got a little over 15 mpg, corrected for tire size using GPS. Speed was very consistently between 70-80 mph. Wanted to get 20 mpg.

I'm hoping some of the mileage masters will have some engine tuning tips for better fuel economy. Boost was plus or minus a few psi of 10 when cruising. Climbed to over 42 psi and 1550 EGTs when i played, only a few times. Timing is 15. 5.

 

[ddechris]

Good thread because I have been disappointed mileage-wise also. My '98 auto has a #11 plate, afe air and exhaust, 265/75-16 tires, 300 injectors, 14 deg timing, 3. 54 gears. So far, I have not broken 15. 5 mpg. I have only owned the truck since Nov. and the mods came with it. Now, I haven't done a full tank highway run to get a decent baseline, most has be rural driving. But, considering I drive very conservitavely, I was expecting 17-18. The fuel filter was changed 4k ago, but not by me, so that is unconfirmed. I know all the fuel I've put in has been ULSD. I put in a BD TC & VB and was surprised it didn't make any difference in mileage, even with the lower stall TC (I still get a little shudder when the clucth locks in at 42 mph /1200 rpm if that is a clue).



My latest thinking is that the #11 plate is mis-matched for an automatic and pouring in too much fuel at low engine speeds when the TC can't tranfer it to the wheels... . but that is just a theory.



I guess I need to get some 70 mph flat run numbers to compare to the others posted.



I'm definitely looking for some advice though.



-Dave

 

[WDixon27]

at low speed low throttle operation the plate is not controling the fuel your foot is, the plate is just the stop that limits how much fuel you can give it at full throttle if the afc is adjusted/working and pressurized out of the way, otherwise the afc stops the throttle till you get enough boost

My latest thinking is that the #11 plate is mis-matched for an automatic and pouring in too much fuel at low engine speeds when the TC can't tranfer it to the wheels... . but that is just a theory.

 

[hsmith]

Mine seems to have dropped lately. Last fill up was only 16. 8. Now, with the ULSD, plate forward, new turbo, enjoying the extra power, maybe the right foot is too heavy too often.

 

[J.BURCHFIELD]

I have had my 98 12v since new. I have always been advised against having a torque plate installed. One Tech. said they "slam" your engine. Feeding it more fuel than it can burn will decrease milage. Keep valves adjusted and the injector pump calibrated by a Tech. that has the equipment and training to do it right. When it has been done right you can feel the difference. Each cylinder getting the same exact amount of fuel makes the engine run smooth. Driving the speed limit is a pain but there is less pain at the Diesel Fuel Pump.

 

[ddechris]

Everything I had read indicated the fuel plate only comes into play at WOT. However, in the latest TDR issue, I was reading a response by Joe Donnelley to a letter in the 12V section suggesting that a #10 plate in a '97 auto could be fueling too much a low and mid rpm ranges. I guess he could have been refering to WOT at low or mid RPM ranges.



BTW anybody have a #8 plate they don't want. Since TST doesn't recommend a #11 plate in my truck, I'd be curious how the performance would change with a plate better matched to the application.



I'm also going to try changing the fuel filter and cleaning / changing the strainer and see if that helps. But not before getting some 70 mph steady flat numbers (egt, rpm & boost?) this weekend.



We've got cross country road trip planned for this fall, so I really need to figure this out.



Dave

 

[PSInt]

#5 Plate

I installed the Low Stall converter from Suncoast and it turned my truck into a REAL DOG !!!! #@$%! Loved the way the converter stopped the engine from spooling up so high, so fast but then I realized why the stock converter is so loose. The turbo spools up at a low speed, increasing boost and making power. Didn't happen with the low stall converter. Truck wouldn't get out of it's own way. I installed the #5 plate and what a difference !!! Tires broke loose, rear end came around... woke me right up ! Oo. I don't claim to be an expert on how the plates work but I know it made a BIG difference in the way my truck runs from low to midrange to high throttle. Lots of black smoke from the exhaust and occasionally from the tires. :-laf Mileage sucked before the mods and about the same afterward. Currently about 13mpg. Most I ever got on the highway was about 14. I bought the tools to bump up the timing a long time ago but I just haven't gotten around to it. From what I've read it should help power and mileage. I really need to get off my *** and gitter done !

 

[hsmith]

Someone some times back said the sure way for better mpg's was to drive barefoot with a pine cone between the right foot and the go pedal. Not me!!

 

[MGunville]

I had a period with some bad fuel mileage, only a few MPGs lost, but the truck was stone consistent before. I thought it was fuel or fuel delivery, but it turned out to be my front brakes were dragging, calipers had seized up from all the salt they use on the roads here. New pads and shoes all around and it gets better mileage and stops better to boot.



May not be the issue here, but something else to check I guess.



Good luck in your findings.