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whats yall's mpg on the highway and in town. and what diesel additive do you use? i have 98 2500 i use diesel clean and my mpg is trash its 14 in town 15 on the highway and i dont know whats wrong
 

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A few things I’ve gleaned here. The biggest regarding mileage is that most reports that seem high in mpg are usually from drivers who go by the gauge, which is far from accurate. Next is if your truck is stock or has had mods done to it. Then your right foot could be the problem.

Do you have oversized tires? If so, did you calculate the additional miles if the odometer hasn’t been corrected?

Mine gets 16-19 in winter and 18-22 summer. It’s pretty stock. There are a few who hand calculate and say they get better than 22.

If you’re getting less (sounds like you are) rule out the obvious mpg killers of low tire air pressure or hanging brakes.
 

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Good mileage, or poor has many different causes. Driver habits, truck weight, speed, altitude, tires, gear train and more. Additives are a waste of money, you will never get enough added mpg to compensate the extra cost, if in fact you get any better mileage at all.

I can get 18 cruising at 70 or 20-21 cruising at 60. I don't do enough in town driving to measure, but if I had to guess it would be in the 14-15 range. I have stock size tires, no lift, no 4X4 and have spent some time tuning my engine for good mileage. Give us an idea of what you have.
 

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I couldnt get better than 16 babying my 95 dually. It was an auto truck with 4.10's and 255/85R16 and timing set too high at about 19. This 98 is dead set on 17.1 with 3.54 gears, nv4500, 285/75R16 and unknown timing.
 

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My 98.5 2500 4X4 Quad Cab Short Bed with the stock Cummins ISB 24V (3.55 Gear Ratio), with 170K attains an empirically measured, calculated median MPG of 15+ City / 20+ Highway (65 MPH) driving (same route/about 100 trips/400 miles R/T) North - South on relatively level East Coast Interstates with no load.

Here are three minor changes which together appeared to have increased highway mileage approximately 2.0+ MPG:

(1) tires - upgraded to larger diameter and width 265 Load Range E Michelin M+S (highway optimized - pressure set to 75 psi);
(2) air dam - mounted a 5 inch wide full width air dam to the bottom of the stock bumper to reduce drag;
(3) solid bed cover - installed a fiberglass bed cover which also cut drag.

I also employ cruise control as much as traffic will allow, keep out of the right lane, and avoid running in the turbulence from commercial vehicles, and keep the revs at near peak torque on acceleration.

Hope you find this useful; it all adds up over the years.

BTW on one recent trip, driving late at night with no traffic, dry, still air, and ambient temps in the 50's the truck turned in 27+ highway - I recalculated twice to make certain … perhaps the Cummins ISB is finally breaking-in, true to its parentage as a mid-frame row crop tractor (AGCO)/bus/marine OEM.
 

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A 24 valve has the luxury of a computer to aid in better mileage, so it's no surprise you can get 15city/20hwy. Also no surprise you had a fillup at 27. I've done that a couple times. The next fillup was in the teens. Sometimes these tanks don't fill completely.
 

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I’ve recently started a thread tracking mine and the difference between my 315/75s and a set of 37x12.5. The difference is actually negligible and actually about .25-.5 mpg better with 37s.

Between 17-18 mpg. Most of my drive is between 45-60 mph.


Sent from my iPhone using Tapatalk
 

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I log every single tank and I know my corrections for tire-size/gearing are accurate. 5spd, 4.10 gears, and highway tires inflated at 55 front/70 back (I drop the rears to 45 in the winter when I'm in one place for a few months, but for most of the year I leave them at towing pressure). Engine timing at 16* but everything else is more or less stock. I get around 21.5 on a highway tank when I drive ~60mph. Closer to 20 mpg if I do 70-75. Around town I can go from 15-19mpg per tank, but it takes me a month to get through a tank if I'm not really traveling so it's really hard to guess why each tank is wildly different -- some might include a couple 150-mile round trips, while some tanks might consist almost entirely of short 3-4 mile trips.

Towing my 11k 5er (pretty much never exceed 55mph) the worst I've gotten was just under 10mpg, and the best was 14.5 mpg. Wind and hills make a huge difference. 12-13 is the norm though.

Jeepyr: I'd be interested to see some pics or a writeup on your air dam? I've considered something of the sort myself.
 

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12 MPG rock solid, calc by hand, (not EVIC).
Scale weight 12,280 Lb.
That's 85% highway driving.
Truck details in signature.
 

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18 highway empty 12 pulling trailer highway. stock tires and odometer correct. only use power service in winter to help with gelling. Install a boost gauge. it is amazing how much fuel mileage drops as speed goes up. I can run 55-60 empty no trailer and only run about 2-3 psi boost (no head wind) a little faster and 5 psi boost, mileage drops fast.
 
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18 highway empty 12 pulling trailer highway. stock tires and odometer correct. only use power service in winter to help with gelling. Install a boost gauge. it is amazing how much fuel mileage drops as speed goes up. I can run 55-60 empty no trailer and only run about 2-3 psi boost (no head wind) a little faster and 5 psi boost, mileage drops fast.
So, no boost = better mileage, correct???
 

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Hope this is on-target; purchased mine 18 years ago for $25 - catalog discounted price is $115 … inflation! All the best. GpR

See: JC Whitney catalog = "Air Dam" AKA Valence

Below is copied from the catalog:

1998 Dodge Ram 2500 Base 6 Cyl 5.9L Replacement Valance
OE Replacement Valance - Plastic, Textured

1-year unlimited mileage warranty
Manufactured from top quality components, Replacement Direct Fit Valance is your inexpensive replacement option for your rebuild, repair, and maintenance needs. A replacement product to replace your damaged or aged factory part. No drilling or cutting required.
All Replacement brands include 1-year, unlimited-mileage warranty.
Notes: Without tow hook holes
Type: Lower Panel
Recommended Use: OE Replacement
Material: Plastic
Color/ Finish: Textured
Series: Replacement Valance
Product Fit: Direct Fit
Replaces O E Number: 55274811
Replaces Partslink Number: CH1090124
Warranty: 1-year, unlimited-mileage warranty
Location: Front
Part Number: 9363
Availability: In Stock
Product Fit: Fits 1998 Dodge Ram 2500 Base 6 Cyl 5.9L
 

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15 is pretty much my standard around town and to and from work. 17-18 highway. Running 35x12.5x20, stock gearing on my 2015. Stock engine. This is going by the computer, never hand calculated it
 

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@ jimduchek, didn't your truck come with a lower air deflector? Mine did.
 

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@ jimduchek, didn't your truck come with a lower air deflector? Mine did.
It did. I guess I misunderstood jeepyr -- I thought he'd found/fashioned something a little taller. I've always thought the stock air dam doesn't go down enough to clear the air around the crossmembers and suspension. Kind of curious to A/B test it.
 
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