Fuel Mileage AGAIN

[SF Jakey]

Ok, here we go again. MY 2002 cc 4x4 sb runs 285/75/16 tires. I calculate my mileage by multiplying miles traveled by 1.1, then dividing by gallons used. My result is never over 14 and usually about 13. What is wrong with this truck? I drive the truck only for long trips so it is mostly freeway driving and I keep the speedo around 70-75 mph, which is about 2100 rpm. The truck has 32k on it and has never seen over 16mpg and that was the first fill up! I'm finding a heavy black residue on the rear corner and bumper behind the exhaust that requires chemicals to remove. Is this indicative of something wrong? I don't feel any power loss or rough running, so I'm really at a loss and the dealer is not helpful at all. No problem he says, it is your tires. If anything, I would think bigger tires running unloaded would help mileage. If this is normal mpg, then what is the 4k benefit over the 8.1 gasser? Hopefully somebody has some ideas. Thanks in advance!

[Jorday]

I have BFG mud terrains of that same size. I've only run them for a few tanks of fuel so far, but the best fuel economy I have seen with them is about 16. I don't know if the black smoke thing is normal or not, though.

[SoCalDMAX]

I would think your tires are 8% larger than stock, thus 1.08 would be the correct factor rather than 1.1, making your mpg 2% lower than currently calculated. :(

There are a variety of factors affecting mpg - tire size, psi, driving style, speed, aerodynamics, quality and type of fuel ( cetane and #2 or winter blend), power boxes, extra fuel filters, running boards, lift kits/ride height, etc.

You'll need to give more info for a better guess. Right off the bat, I'd say your cruising speed is a little high. I've gotten as high as 19.9mpg for 2 or 3 tanks in a row at 55-60mph, but normally get 15.5-16.5 mpg in normal city/hwy commuting, and I drive pretty aggressive and at 2000rpm cruising on the hwy.

Raising the front drastically changes the aerodynamics, as well as running boards. Run the tire pressure close to max. as long as you can stand the ride. I've heard from everyone that better fuel filtration will result in 1 or 1.5mpg better mileage.

Hope this helps, Steve

[jcummins]

I've gotten over 20mpg....but....I can't do it without using the cruise, and keeping the rpms below 2000. I have 265/75-16 and I'm just a tic under 2000 at 70mpg, by the speedmeter, with is actually being 72mps by GPS. For you, 75 by your speedometer is probably 78-79. I think your running faster than you think.

[LA DMAX]

SF,
Ditto what Socal and jcummins said. There are alot of factors that will change your milage. It seems that for you it might be your speed. Try keeping the motor at or below 2000 rpms and see what happens.

I run the stock pizza cutters and get 18-18.5 mpg daily driving and 19+ if on a long trip and the speed doesn't get past 70. If I get up to 75+ my mpg's start to drop. There were alot of discussions about a year or 2 ago about increasing wind resistance with increased speed dropping mpg's. I believe it does have an affect, how much? Not sure. Hope it helps.

LA DMAX

[Spartus]

285/75/16's, front bars jacked up 1", and a 200lb tool box in the back. I get 15-16.5 mixed daily driving, and 20+mpg on pure highway driving... I also get 14-16mpg towing 6,000lbs... :D

I'm very very happy with my truck. smile.gif

[Big Tow]

I am getting about the same with my '03. I have BFG 285s and a cab high topper on the truck. Unloaded at 75-80mph actual I get no better than 15mpg. I have 15k miles on the truck.

Drive slower to get better milage???? That stinks! I have a house in CO and in MN. I have to drive across scenic Nebraska to get from one to the other. The limit is 75 and I regularly cruise at 80-85 actual. making the 1400 mile trip at 60-65 would add hours to an already long drive.

I have more bad news, not that anyone wants to hear about my cummins trucks but, they do MUCH better on fuel. My QC short box gets 19 mpg on the same trip, same speeds, same gearing, same tires and it rides much higher than the D-max.

I also have a buddy getting similar or better milage with his 8100 allison crew cab 4x4. If I had to do it all over again today, I would get the 8100 :(

[ih1466]

I think we all need to get a dodge or a ford. Everybody that I have talked to with a dodge gets 20-24mpgs empty or towing 20k. The ford guys say 18-20 doing the same. What is wrong with our trucks. I saw 20mpgs once in the summer. I run stock size tires. Summer I get 16-18 and winter 12-16. When I pull my GN and pulling tractor I get 8-10. With my 4-place snowmobile trailer with 4 snowmobiles or 4wheelrs I get 13-15. I know it matters a great deal how you drive it. If my dad drives my truck he gets about 2mpgs better than me all the time.

[chipper]

1h1466,
If you believe all of the above, I have some waterfront property in Tuscon Az that I would like to sell you! :D

[Big Tow]

I don't think my 7.3 Ford gets much better milage than the D-max. I think that when loaded I was getting 10-11mpg with my '01 D-max and 11-12 with the Ford. My '03 Cummins trucks get about 12 loaded. I do notice a pretty big difference when empty though. The extra speed doesn't seem to effect the Cummins near as much as the D-max.

It has nothing to do with waterfront property ;) No more than the guys claiming 20+ from a Duramax :rolleyes:

[ih1466]

No I know with the power the diesels are putting out today you are not going to see the big mpgs. You can't get something for nothing. A second OD would help the duramax alot for empty and light towing. I had a friend with a 99 PS that never saw 13mpg even empty and pulling 4 4wheelers only got about 8mpg. They just got a Duramax about a month ago. Have another friend with a 2000 cummins dodge that used my truck and trailer for a few weeks this summer to haul big square bales. I drove the dodge to work and few summer weekend trips and the best I got with it was 16mpgs. His dad went out and got a Duramax after hauling hay with my truck. If you use them they will use fuel!!

[Spartus]

The MPG on the Duramax's seems to vary quite a bit from truck to truck... at my shop there are 5 of us that have Dmax's... 2 are extended cab short boxes, 2 are 4 door short boxes, and one is a regular cab long box.... I get 20-22mpg on the highway with my extended cab. This is with filling up on the highway btw.. Two of the guys at the shop are lucky to hit 17mpg on the highway with thier 4 doors. The guy with the long box regular cab has seen 23mpg several times. But one of the guys with the 4 door only gets 10mpg towing a 5,000lb trailer... Then again he's still got the factory fuel filter in at 35k. :eek:

[SF Jakey]

Wow, this is a great response. At lest I'm not alone with the poor mileage. What brand filter do you replace the stock with, or is it a whole different filtration system? I did turn up the torsion bars to clear the 285's, so maybe that is hurting the economy some. Its not the end of the world, but it sure is frustrating knowing some are getting such high numbers. I would rather travel at 70-75 mph and get 14 than go 55-60 though.

[Colorado Kid]

I have no beach front property, for sale or otherwise, but I do have a D-max that has returned over 20.0 MPG on every tank, unless I was towing. The only exception was when I filled in Rock Springs, Wyoming on 9/6/02 after a run from Longmont, CO with a tank average speed of 70.4 MPH. (In otherwords into the Wyoming wind on I-80 at 80 MPH most of the way). That tank was 19.7 MPG. (On the way to a certain hill in western Montana) ;)

I've entered date, odometer, hour meter, gallons and cost for every fuel fill in an excel spreadsheet since 2/21/02, the day I picked it up. Lifetime MPG (including towing miles, which average about 14 MPG) is 20.78 MPG as of the last fill.

It is 2WD, 6-speed and stock, right down to the Bridgestones. Only sees the high side of 2000 RPM when it's honor is in question or in 6th gear. Rarely run more than 5 MPH over posted limit . . . bright red trucks attract attention, and traffic engineers are not supposed to get tickets. :eek:

Towing the 5th wheel I cruise right at 2000 RPM, which is 68 MPH. Any faster just seems to change the number of fuel stops, not the arrival time.

[James S]

Hey There,

This is vary interesting. I have a crew-cab, long-box, four by four, and get great milage! Typically, 15 to 17 in town, [or 18 to 20 imperial] and on the highway, 19 to 22 [or 23 to 26 imperial]. I typically drive at between fourty and fifty miles an hour in town, and sixty-five to seventy on the highway. I've acounted for the 265 Bridgestone Revos. I don't know if it is them, combined with my Leer 122, canopy, my ATS dual exhaust, screen/or cold front, whatever, but I couldn't be happier! Let's get some numbers from 2500HD owners, ONLY, indicating cab/bed length, and accessories such as exhausts, fronts, canopies, filters, etc, to try and figure out this difference in milage. To me it doesn't make sense. The only things I can think of are, clogged filters, you need to change tires, the mass-air-sensor has that piece of plastic in it from the factory thus it is plugged causing more fuel usage ETC, body lifts causing poor arro-dynamics, etc. When some of these numbers are given, let's try and get some COMPLETELY stock trucks, of different cab/bed configurations as well, because maybe it is just the mods, and not the engine, or truck itself. Let's get this sorted out. Talk to you soon.

James

[Idle_Chatter]

Colorado Kid is right on the money. This debate erupts every three weeks or so with many owners wailing about 15 mpg and calling "bull" on 20mpg numbers and many more reporting mileage in the 18+ range. I've had an overall average over 18 mpg and typically get 18-20 running empty. One note is that the best tank I ever got: 20.3 was running steady at 55-60 mph. These trucks LOVE that speed and really sip fuel in that range!! I suspect a lot of the low mileage guys don't operate near that range and if that's true will rarely see the economy potential of the DMax.

[SF Jakey]

Please fill me about the mass air sensor plastic piece. This sounds very possible, since I smell heavy diesel in the exhaust and I've always complained that I felt the truck was getting too much fuel. Is this something I can find out myself?

[WillowCreekStable]

I've got 60,000 km/37,500 miles on my truck. The only thing my truck has that isn

[Murray the Cop]

I have an 03 SL extended cab long bed 4x4. I have never seen better than 17. Before or after mods. I use the truck for a daily driver to and from work which is about 45 miles one way. My average mileage when I fill up is 15 to 16 for the tank full. This is mostly highway at 70 to 80mph. I tried the 60 mph to work for a tank full and it made no difference.Towing an aprox. 10,000 pound 5th wheel I get 8 or 9. Still beats the 01 Ford V10 I had before this one. Seven around town,12 hwy, with my wife driving it. Mods now are juice w/attitude,4inch bully dog, ams oil air filter.As I said before the numbers are the same.We'll see if the Nicktane/cat pre filter makes a difference.

[James S]

Hey There,

A couple of years ago, some were having TERRIBLE milage. It was found that when the Mass Airflow Sensor was installed on the trucks at the factory, they forgot one thing. There is a SMALL piece of protective plastic that is taken off the sensor itself, and snipped off with a pair of scissors. If it wasn't cut off, it would be blown up into the sensor by the wind, plugging the sensor. As such, no air getting to the engine, the more fuel it would use, thus causing TERRIBLE fuel milage. Ask your dealer to check it for this. It also could be that your mass air-flow sensor, [MAS] is dirty and needs cleaning. I cann't remember how to do that, but do a search on the forum, because it has been covered befor, or have your dealer clean it. Do this soon, NOT LATER! This is entirely a guess on my part, so I might be wrong. Keep us posted though on what happens, because, even with your tires, etc, your milage shouldn't be this crappy! Talk to you soon.

James

[dakotakid]

I certainly can't brag about good mileage. I have 33,000 miles on the truck right now. I haven't had many tanks over 16 when empty. Most are in that 15 range - or less. Pulling the camper (32 ft travel trailer) I have never gotten over 10, and the worst was a few at 6!!! I drive fairly hard, but expected the mileage to be better. Pulling the trailer with a stock truck (only about 1000 miles on it) to ID and back I averaged just over 7 mpg. The 1st tank was kept below 60 and got 7. Several tanks were pulling at 75-83 and still got 7.

At 25,000 I made the same trip with the same camper. Updates on the truck were a switch to 235/85 R16 tires, K & N air filter, and the Predator. I ran the Predator some on 60 hp, some on 40 hp, and some at factory hp. My average mileage improved to a little over 8 mpg, and my two best loads were just under 10. Incidentally, the best two tanks were at factory settings. My wife did some of the driving this trip (doesn't drive near as hard as me) and I couldn't tell the difference in mileage. I like the truck and the power, but wish the mileage were better - and the fuel tank were bigger!!
I pulled the same camper with our 6.0 litre Suburban and average 6.5 mpg, but the power was definitely lacking. I kept the speed at 65 most of the time because I didn't have the power to push it much harder without the tranny doing a lot of shifting...

Pat

[MikesToy]

I have 75K on my 2001 EC LB 4X4. The best I have seen on the hiwy is a little over 20MPG. I cruise around 80 when empty. Around town I get between 15 and 17 MPG with an average mix of 50/50 surface and freeway miles. When I have my 13K 5th wheel on, it falls to between 7.75 (worst)and 11.2 (best). I pull around 70 to 75 most of the time.

I put a Banks Stinger kit on the truck and my mileage stayed about the same, but I pull my 5th wheel 5+ miles per hour faster! :cool:

[afp]

I ahve 90 HP juice always set at that level and 285s. Best mileage with the 285s on the freeway was 21.9 mpg. Best with the 265s was 21.6 mpg. In town is 14ish. All of those are empty figures.

Blaine

[James S]

Hey AFP

What speed were you going with the 265 tires when you got 21.6 MPG, and with the 285 tires when you got 21.9 MPG?? What RPM were you at as well? What kind of milage do you get right at eighteen-hundred RPM's, and what speed are you going? This might help some who are having poor milage. My milage numbers were all at eighteen-hundred RPM's. Idle Chatter is absolutely right, the Duramax LOVES that RPM!! Talk to you soon.

James

[Murray the Cop]

Can somebody give me more info on the mass air sensor? Where it is and how to check if the guy who installed it forgot his scissors that day.Thanks
Anthony

[James S]

Hey There,

I would take it to your dealer, and have him check it. If it is touched with your fingers, the alcohol from your skin will damage or ruin it, so I have HEARD. Ask around and others might have other suggestions. Hope this helps.

James

[SoCalDMAX]

LOL. :D

I think you meant it might get contaminated with oil from one's fingers, and you were thinking about cleaning it with alcohol.

I doubt he's likkered up enough to be oozing alcohol from his fingers. ;)

The easy way to get a look at it is to loosen the clamp on the air intake hose right where it attaches to the airbox. Pull up the hose and look inside, at the top will be a pair of posts and a very fine coiled wire between them. I don't know what the excess plastic piece would look like, but it should be obvious if something's blocking it.

Regards, Steve

[OilMan]

Its the 3.73 rearend. Better mileage would result in vehicles that had a 3.42 rearend, if that was available. Really wonder what a 3.08 would do?

I pull heavy on occasion, but most of my driving is unloaded, with some weight of tools. A more of a highway ratio would be to my liking, since my truck has lots of power. New Duramax engines this year have even more.

I hope the different ratios will be an option for the Duramax equipped trucks someday.

[chuntag95]

I have an 02 CC/Short bed. I have a Roll n lock cover, 4" exhaust and have gone to 265s at 30k. I run the 120 Pred. I saw a 1 mpg loss when I went up in tires. I changed the settings with my Pred immeadiately. Never left the parking lot of discount tire til I was done. I "assume" my speedo is accurate based on highway timing and mileage matching. I have had 1 instance over 20 mpg and 3 around the 18.5 mark. My lifetime average is a smidge under 15 with mostly city driving. I have seen the Pred vary mileage with the 120 hp yeilding the best results so far.

My father-in-law has an 02 extended/long bed that gets 19 all the time. He drives conservatively, but will tow and heavy often. Don't understand it, but I know the variation is there.

[grape]

for all you guys that are worried about fuel and drive 55-60......STAY IN THE RIGHT LANE for the rest of us.

[afp]

James,

Speeds were 65-70mph for the average cruise. Ocassionally I might increase 5 mph above that to pass someone. I think I am at 1800-1900 rpm at these speeds.

Blaine

[SoCalDMAX]

Originally posted by grape:
for all you guys that are worried about fuel and drive 55-60......STAY IN THE RIGHT LANE for the rest of us. Amen! :D I drive whatever speed feels comfy and the mpg ends up accordingly. The one time I did do 55-60, I was in Tahoe and it was really slushy. So I drove like there was an egg on the pedal, ended up with 19.9mpg by accident. But normally it's not worth the effort.

Regards, Steve

[dakotakid]

I used the Dmax to pull a large flat bed trailer and skid steer yesterday. First leg of the trip was 120 miles. Used cruise & tow/haul the entire time. Set the cruise at around 69 (2000 rpm). It stayed at 2000 rpm almost the entire trip - only down shifting on a couple hills. Had about an hour of idle time while unloading the skid steer and loading another back up. Return trip the cruise was set at 67-68, and the tranny was shifting quite a bit more, so 40-50% of the time I was running at 3000 rpm, the rest at 2000. Filled up halfway back home - 7.3 mpg - OUCH!! Can't believe it won't do better than that. The last 60 miles it jumped all the way up to 8.6 - I set the cruise a little faster because it was staying at the 2000 range much better. Sure would be nice to see numbers better than that!!

Pat

[andrewfessler]

I just completed a week long trip from Ohio out east to NJ, NYC, down to Baltmimore, to DC, back to Baltimore and finally back to Ohio.

Drove 1800 miles, pulling a 18ft cargo trailer with approximately 2,500 lbs. My total trip average was 10.1 MPG. I generally don't run more than 5 MPH over when traveling long distances. The truck rarely went into OD, except for up a few "hills".

A month or two ago, an unloaded trip down to NC got me trip avg of 18.6 MPG.

[Cliffee]

I live in Phoenix and typical city for me is 17-18 and highway 20-23. I drive pretty normal. Milage on truck is 18k with stock tires. I just pulled out my Amsoil Air filter and installed the stock paper and milage dropped 1 mi/gallon. across the board.
Once had dealer forget to tighten clamp around intake to airbox and mi dropped to around 12 mi/gallon.
Iam pretty happy with milage, unfortunately the rest of truck is of low quality.

[BadDog]

Well, mine is stock and maintained with stock components and I have yet to make it over 19 mpg. And that took a steady 65 mph flat road (I10 across Texas) and empty with no women in the rig (aka run out a tank before stopping). I get from 12-15 with any load load. Worst yet checked was loaded to about 15.5k gross through the mountains at a bit above 12. Better than a gasser, but not what I expected.

[20050528|8|000731|000000|205.188.117.71]

My last truck was a lifted 99 Super Duty with 35

[Stage1]

O3' 3500 crew cab 2WD, with 12,000 miles mainly used for long trips. Tires are upgraded to 235x85x16 Michelin XPS ribs.

Lowest milage is about 9.5 MPG towing 30',12k Box trailer up WV mountains in 2nd gear at 2800RPM. Typical MPG for this load is between 10 to 12MPG. Local winter MPG wo/trailer is around 13 to 14.5 and summer is 15 to 16. From my experience it seem that changes in road grade significantly effect fuel mileage. Therfor suggest that another factor effecting fuel consumption is the grade changes in the roads you drive on. Also believe tires can have a 1 to 2 MPG effect as previously stated.

Also glad to be back w/the forum, I have gone for a while.

[1BADDMAX]

Running Dunlop Mud Terrain's 255/85/16 (33's). I can obtain 17-18 in town. I usually see 19-21 mpg on long highway trips. Speedometer is corrected via Predator. The 6 speed definitely helps the mileage. Mileage dropped about 1 mpg with the addition of the mud tires.

[Idle_Chatter]

The variations in mileage that the DMax sees has been a continuing source of conversation. I've been very happy with my results. One thing that I learned in my previous diesel, a '99 6.5TD Tahoe, is that there are "sweet spots" in the diesel rpm range that really give great mileage and being as little as a couple hundred rpm to either side will show significant economy dropoffs. I don't miss much in comparison to the DMax, but one thing that I do miss is the electronically-controlled wastegate on the Tahoe. I could drive on the boost gauge on the highway and really increase my economy. If the system was boosting, it was burning fuel and running less efficiently. I could "tune" my rpms and speed to hit a spot where the computer was dumping boost because the engine was running "sweet." I got over 17 mpg running a 5x8 loaded U-Haul trailer across the Illinois/Indiana turnpike once this way!

[SoCalDMAX]

Tom, I remember you mentioning this before, and it certainly makes sense.

So are you saying that the sweet spot is going to show lower boost than on either side of that rpm? Have you found that sweet spot on this truck? Do you think it's repeatable on other Dmaxes?

My next door neighbor had his boss buy a D/A 3500 flatbed based on my ravings, and he's a little disappointed in the mileage numbers. They're getting low 12's or 13 essentially unloaded or very light loads. These are employees driving a co. truck, so he figures they're driving a bit fast or idling a lot. I told him to see if keeping it under 2000 rpm would help. We'll see.

I've thought of sneaking over and installing my stock Juice Box on it without telling anyone, as a joke. But of course something bad would probably happen and it wouldn't end up so funny...

Regards, Steve

[Idle_Chatter]

Well, it's not so easy in the Dmax, Socal. That's what I miss about the Tahoe wastegate control. I could watch the boost gauge and it would roll off about 3 or 4 pounds of boost running steady on level road in one of those good ranges. The DMax mechanical gauge just cycles back and forth between 3 and 6 pounds in the same situation, being purely mechanical. I guess trial-and-error is the only way with the DMax, so far I've found that mine much prefers 1800-2000 rpm over 2000+. Problem is that the sweet-spot ranges are not "fixed" at one rpm and will vary up and down from day to day due to fuel, temperature, wind, and other factors. Maybe I can work out some kind of similar information from EGTs, but I haven't seen anything that seems logical so far. I'll have 14 days and 3500 miles of a Florida run coming up in a couple of weeks to try and work it out. And don't worry, folks, I'll be in the right lane pulling my box trailer out of your way and will roll right by you when you make that extra fuel stop and STILL get there just as soon as you do! :D

[Bullseye54]

I have a 02' 3500 CC w/235 tires & a 2500 EC SB w/285 tires speed-o corrected w/Predator.I get solid 16mpg w/3500 on reg tank city & "country" driving.With the 03' 2500 gets 14-15mpg the same conditions with me or wife driving.Highway the 3500 gets 18 & the 2500 gets around 18 also.Towing our 11000lb 5er the 2500 gets 8.5-9mpg,haven't towed with te 3500 yet.They both run different from each other engine wise,nothing major just different.

[Stage1]

Just returned from a 1600 mile round trip to central MN pulling an empty 3000lb. open trailer going and a loaded 9000 lbs. on return. Truck is 03' 3500 wo/modifications. Generally I believe that this truck delivers good fuel mileage. However what effects my fuel milage is hard for me to fully understand. For example going to MN fuel milage ranged from 11.2 up to 12.8 MPG ( factors include higher speed, head wind, very cold temperatures), return trip 11.8 to 13.4 MPG ( factors include much lower speeds, tail wind, warmer temperatures).
For example the best fuel milage was at about 50 MPH because of snow and icy roads. What does this mean? do we need another OD gear to reduce engine speed on the highway?

[deerhunter7]

When you talk milage on this Duramax Engine ,pick a number between 12 and 19. Thats how much mine varies. There are so many factors involved all one could do is take total milelage and total fuel burnt and thats what you are getting.People in the warmer climates will have higher numbers than us that have 10 months of winter and 2 months of road construction.. :eek:

[chuntag95]

For all of my tanks of fuel, miles per hour correlates very well to miles per gallon. The faster I go, the better the mileage. The R squared value is 0.71 for you geeky types. tongue.gif

[dmaxmule]

I am curious. What is the R squared for?

I do not quite grasp :mad: all of the number crunching and such that goes on here at this site. I understand:
hours per gallon
miles per gallon
However; as for the rest of the numbers that I have seen on this site over the past year(can't remember any specifics)I sit here puzzled :confused: at what they are and why you guys figure them.
dmaxmule smile.gif smile.gif

[Viking]

dmaxmule, do not wory about it. It is only for certain people.

[turbovair]

Wind drag is the big problem. Wind drag is exponential. That means that if at 35 MPH, wind drag is X. If you increase speed to 70 MPH, you would expect wind drag to be 2X.In reality,its 4X. So,wind drag is 4 times higher @70 MPH than it is at 35. Your computer senses the additional load and adds more fuel to compensate, with the effect of lowering fuel mileage. Diesels behave very much like gas engines when being worked hard, the mileage drops.It takes roughly four times the energy to propel an aircraft @ 700 MPH than it does @ 350.If you want better fuel economy, slow down.

[DIESELMAX403]

It's interesting to see what others are getting for mpg. I tend to do better than average unloaded, but worse than average loaded.

With 14K miles on the odometer, I get 18-19 driving to work (70 miles city/highway roundtrip, computer showing avg speed of 45 mph). If I abuse it, my mileage rarely goes below 17 mpg. Cruising on the highway at a steady 65-70, I get 20.5-21.5 mpg. I'm very happy with this mpg considering the truck weighs close to 7500 lbs. smile.gif

Now towing is a different story. With an 8000 lb travel trailer, I can barely get over 10 mpg driving 60 mph on a flat country road. Normally I cruise between 65 and 70 mph between Houston and Austin/San Antonio/Dallas on the highway and I barely get 9 mpg. Since my truck does great unloaded, and I do not hear or feel anything out of the ordinary while pulling, I tend to think that my truck is operating normally. I usually pull in OD except for a few hills where I have to downshift to 4th to hold my speed from dropping. I do not know what to think when I hear people are getting 13-14 mpg pulling the same weight in the hills. I wonder if they are averaging in some non-loaded distance when calculating their mileage or if for some reason, their wind drag is drastically improved over mine. And then there is the possibility that there is something wrong with my truck and I do not know it. I guess I'll keep wondering. :rolleyes:

[DonG]

DIESELMAX403,
I typically get 9.5 to 10.0 mpg when I tow my 14,000 lb. trailer at 60 mph. So your numbers appear low.
Several possibilities:
1. Your trailer is VERY tall and is causing a lot of wind resistance. (Mine is 12' 4" tall).
2. Your trailer tires are not fully inflated.
3. Your trailer brakes are dragging.
4. Your trailer actually weighs about 12,000 lbs. when loaded.

Don

[Lone Eagle]

You are towing in OD? Later! Frank

[FATBOY]

285 75 16 bfg muds 14.7 back to the pizza cutters 19.4 yes i added calculations pizza cutters for ever

[DonG]

Not sure who you are addressing Lone Eagle, but if it is me, I tow very much like described above.
I tow in OD on level ground and gentle hills. I will push it into 4th if I see a big hill coming, or a series of hills that may cause the transmission to hunt too much.

I have never used any power chips.
Don

[Inspector]

I have a combined weight of around 21500 with my fiver with half a tank of fuel and our usual road load. This is about the same wieght that I pulled with my 93. The fuel milage is about the same between the two trucks. Pulling 8-10 1/2 at 70 mph. The 03 is chipped and the 93 has had some work done to it such as a GV and exhaust/intake mods pump turned up, cooling upgrades and intercooled, gauges of course. Tire sizes on both trucks are stock. Unloaded 15 to 18 both trucks. The Dmax has improved somewhat as it breaks in but not eyepopping. I'm happy with the way it pulls and I'm not shifting gears anymore.
Not to worried about the milage. I just put the attitude in level 2 set the cruise at 70 and let the trans do the thinking and enjoy the drive.
Denny

[Lone Eagle]

I was asking that of DIESELMAX403. Later! Frank

[chuntag95]

Originally posted by dmaxmule:
I am curious. What is the R squared for?
Sorry I didn't see your question sooner. R squared is a value in statistics that says how good the correlation is. For example, if I have an R squared of 1 (the highest it can be) then I would be able to predict the MPG from my MPH every time with no error. The lower the R squared the more error in the calcualtion. Some might say it is 71% confidence for an R squared of 0.71. Some people don't like to look at anything below .95 and other .5. It's a geeky footnote to how accurate the model is in predicting an outcome based on the variable you have choosen. In my case, using MPH to predict MPG. Of course there is error for idleing, filter changes where fuel is lost or mods where fuel is lost. You also have the error from the pumps, fuel quality, blah, blah, blah. Taking into account the list of stuff I know will change my MPG, I think 0.71 is saying my speed has a lot to do with my MPG results. It's not perfect, but then again, neither am I. ;)