Engine/Transmission (1994 - 1998) Milage

[JJW_ND]

AFC - fuel plate - auto - Big City traffic

Josh, you might remeber my truck from Mikes. Like Vaughn, I run 450 - 550 at 70 mph (2k RPMs exactly) and 2 - 4 pounds boost. When I was stock I ran many 50 degrees warmer and 2 pounds more boost at 70. I have even larger tires (285/85R) but have my speedo GPS corrected.



The last couple of years I have ran a yearly overall average (pulling - city - hwy combined) of around 18 mpg.



In town driving big city traffic, a loose AFC and an auto will be hard on economy. If you have ran a long trip, does you mileage get better on the road when driving a steady speed?



If you never see smoke then I agree something is wrong, if you see smoke pretty regurlarly, that is a big contributor to your poor mpg.



I agree that our 12v trucks should do high teens - low twentys when cruising 65 - 70 mph. Even in the dead of winter and all in town driving I still get 17 - 18. Need a trailer in tow to get less. From all I have talked to with similar trucks this mileage is pretty typically . . not on the high side.



jjw

ND

 

[JoshPeters]

No matter what I do my milage doesnt change. I took a trip last weekend from Anoka, MN to Alexandrea, MN. All Hwy cruise set at 68. The milage on this post is from that trip.



Josh

 

[bkroupa]

At 65mph my truck is just under 5 lbs of boost & 600 egt. I know the dually has more drag, but it does seem to be working a lot harder at cruise than my SRW. What kind of tires & tire pressure are you running?

My truck averages 22. 5 or better running empty with the 285's & 3. 54 gears.

 

[MDW]

Low fuel pressure can cause bad mileage.

 

[SpicyJam]

Uhh I don't think so... . I have enough problems with everything else, I don't need a VP and LP to give me issues! I like my properly valved truck! :-laf



Josh

So what are you really saying? Sorry Josh I had to get that one in. But then again,

 

[JoshPeters]

At 65mph my truck is just under 5 lbs of boost & 600 egt. I know the dually has more drag, but it does seem to be working a lot harder at cruise than my SRW. What kind of tires & tire pressure are you running?

My truck averages 22. 5 or better running empty with the 285's & 3. 54 gears.

Right now I'm running (to much) 50psi of pressure in all the tires(new tires and it made no difference). I chalked the rears and need to lower the pressure so the tires wear properly. I don't think a Dually has THAT much more drag.



Fuel pressure, that's one I haven't heard before. I replaced the overflow valve about 10,000 miles ago... . I may still have to check my fuel pressure.....



Josh

 

[bkroupa]

I didn't think so either, but if it takes more boost & higher EGT's to cruise the same speed, something is holding you back. I'm running ~8lbs boost when towing our 30' TT at 60mph & get 14-15 mpg towing, 13-14mpg towing 65mph @10lbs boost.

MDW has done some work on my truck, he knows these trucks pretty well.

 

[JoshPeters]

It's something to check! I don't get it... . It's been pretty much like this since I bought it 3 years ago. Bone stock till now... same milage. I did check the fuel pressure once a bit over a year ago and... . if I remember right... . it was around 27-29psi.



Josh

 

[CSnyder]

Josh, I was thinking about this today and failed to mention something in an earlier post. Since you wrench for a living do you adjust your rear brakes at every oil change and maybe getting them too tight? I know I was bragging about how good of mileage I get earlier but I can definately see a huge difference on mileage when I set my rear brake shoes or my trailer brakes up.



If you had a good electronic truck I could maybe be of more help. I can't claim to be an expert of these trucks but I have sure learned A LOT from Aron this last year. That guy is a whiz!

 

[DHorstman]

My truck cruises at 70-72 with 10+psi boost. Small hills will pull 15psi, empty no trailer. Slap a 5K trailer on and 20-25psi on bridge overpasses. Heck my motorhome cruises with less boost at same speed than my truck. Mileage averages ~16 running the 285s and ~17-17. 5 with stock tires. Have seen best of 19. 5 for a 770 mile highway run empty, anywhere from 55mph for many miles in construction to 75mph.



No #s for EGT, never installed that gauge(some day), don't really tow anything with it for much of a distance. I really didn't notice a MPG difference when I slid the plate forward either. Not thinking its my rear brakes, do all the work myself and haven't pulled the rear drums since I bought it 1 1/2yrs ago, even after running it thru the mud .



However I am begining to suspect my lift pump is going south. Getting a clacking sound that's from the LH side of the motor. Injector plungers coming off the cam trying to suck the fuel? Need to get a gauge on that soon.



Truck has 168K, stock injectors, stock timing, stock trans.

 

[EBottema]

I am also only getting around 16mpg lately. I think my 35" tires with 3. 54 gears have caused that one. With 285's i was getting between 18-20...



gears soon to come

 

[Neibe]

I've been driving more conservatively lately and my mileage went for 17 to 20 not going over 55 in 55 zone or 70 in 70 zone.

 

[Jeff H]

I have 0 plate,370 nozzles,3k govs. Timing at 19. 5

3. 5 gear, 285/75 tires. I average 21 mpg in the summer.

Training wheels cut into mpg a little. Lower gear 4. 10 cuts a little too.

Check alignment. Tire psi of course too. Keep em pumped up.

Make sure air to air intercooler has good flow going through. I cleaned mine a couple years ago. Plenty of dust and fuzz in the fins.

Check boost line hoses and clamps for tightness.

Check fan clutch if ya have one?

I like to add some fuel additive to the tank at least once a month. Keeps things good and clean.

 

[AndyJohnson]

Just curious i have a bad fan clutch and just haven't put it in yet. does that really affect millage much i mean if it's sliping would'nt that give you better milage?

 

[K5IP]

My 95, 5spd, 3:54 gears 4x4 2500: (215 injectors)

At 65 mph flat and level, no headwind, sea level:

Boost = 4psi

Egt = 500

milage 20-21 corrected.



I agree with several other posts, you are needing too much fuel to keep you going as indicated by higher boost and Egt levels.

Why? what do I know!

Rog

 

[JoshPeters]

I agree with several other posts, you are needing too much fuel to keep you going as indicated by higher boost and Egt levels.

Rog

That's what I'm wondering! I can't seem to find out why. I would think cruising, regardless of fuel plate and injectors I should still be able to get decient milage. I can understand crappy City milage, but Hwy? A diesel only uses as much fuel as it needs to sustain an RPM..... So why does mine seem to be taking more?



Josh

 

[bmoeller]

Josh, do you have the 14 housing on a stock turbo? If so, you may want to try a turbo with a 4" outlet. What do you have for exhaust? Straight thru?

 

[JoshPeters]

Right now I'm running a 12cm housing. I've got 3'' down to just under the cab then it's 4'' straight all the way out.



I've wondered about the exhaust. One of the MNTDR members is getting 22+ now that his truck is twinned.....



Josh

 

[Cooker]

I don't think the exhaust is your problem.



I'm sure a larger turbo would help your MPG's as it is quite common. Although it may be a solution I don't think it is the solution.

 

[2Gen3Gen]

:-laf

Gosh I feel really bad now since I got 20. 5 pulling a 32' gooseneck from Lacrosse, WI to Rapid City, SD going between 65-80 all the way on the interstate. Maybe it's time to get a 24 valve Josh??? I have gotten as good as 26. 7 just driving the truck around empty on longer trips. Chris

Hmmmmm, I havent seen REAL figures like that since I had my 90 1 ton 4x4 5 speed. Hmmmm I think you may need new batteries in the calculator or the over head is way off. that just dosnt seem possible. I have several friends that have the same rig as you and they are lucky to see 20 mpg down hill with the wind behind them. Not that Im saying you are not really getting the mps's but... If you are getting thise figures, that is great. I would recheck your math. i just find that hard to beleive. Kinda like the salesman when I bought my 04 305/555 that claimed I would get 30 mpg on the highway and 25 around town, just because a friend of a cousin of his X broher in laws boss's son's buddy at school, knows someone who has a buddy that ran into a guy at a truck stop that heard at the bar a few weeks earlier inthe next table over, two guys talking about how their Dodge Diesel got this really great mileage. . Hmmmm