Diesel Gas Mileage

Hello all…I am wondering what I am doing wrong with my diesel. Its a 2005 Chevy Duramax crew cab with a topper. I currently have 53000 miles on it, and I am running BF Goodrich All Terrains. I have NEVER EVER got better than 15 miles per gallon on this truck!
I change oil every 3-4 thousand miles, change my air filter every 10k and even change my fuel filter every 20k. I am a normal driver, I don’t have a heavy foot!!! Most of my driving is to and from work, which is about 20 miles, some city driving and some freeway! And of course pulling the boat on the weekends and durning the week sometimes.
But my question, I see and read so many post about people with Diesel trucks getting average of 17, 18 and some even 20+ mpg!! What gives??? I can’t seem to break 15 mpg on any tank! Always as constant 14.7 or 14.8 mpg.

Does this type of gas mileage really exist on diesel engines or is everyone caught up in the hype about how good they mileage should be and lying to us?????

Just curious and looking for honest answers!

Thanks!

Oh by the way this truck is a stock truck except for the tires!!!

Cal;
with your city driving and with pulling the boat, you may want to consider re-programing the computer with a super-chip. It may help????

It sure does seem low though for mileage????????

Cal, I was getting 12 with my 7.3 Ford Super Duty. I was having the same issue. I went back to the F-150 with the gas 5.4 and I get 18.5 MPG. And it pulls the boat like a dream.

I am sure Chevy may be the same way. Unless you are pulling something really heavy, or a boat very long distances at high speeds…I don’t think the diesels offer any benefit. I am not trying to start a diesel bashing post, or whos is better than whos…Just what I found owning one. Plus the added extra maintenance that you cited was enough for me. Oil changes are expensive on those big motors! Not to mention the cost of diesel!!!

Cal, What weight oil are you using? When I bought my 06 power stroke diesel the dealer suggested running 15/30 year around. I was consistantly getting 17.8 mpg. This past December I took it to a local mechanic to have the oil changed. After i picked it up I noticed the tag said he put in 10/40. My mileaged went down the drain. I could not get any better than 15.8 mpg. I took it back to the dealer on the next oil change and my mileage is right back up to 17.8 and even 18.3 consistantly. I am no mechanic but it was very obviuose that oil weight made the difference in my case.

Chevy has 4 generations of Duramax engines. LB-7, LLY, LBZ and the 2007 with the emissions canister on the exhaust. I’m sure yours is the LLY and I have heard of over heat and poor fuel mileage problems with that engine. Are your tires Dia. larger than stock? Are this hand calculated mpg figures?
What to do…
Have the engine reflashed with the lastest program? Tell the service writer you are getting terrible mph!! You are, and they are aware of it.
I had a 2002 Duramax short box extended cab and got 20 mph o n the interstate unloaded. Now I have a 2003 3500 dually extended cab and get 17 – 18 unloaded and 15 with my pickup camper on it.
For a lot of good info. go to http://www.DieselPlace.com and use the search button on the upper right hand side of the page.
I change my oil every 5K and 10k is what they req. for fuel filters.
Your mileage is weak and you should get that 17-20 mileage!

I too had an oil burner and got rid of it for a gasser. I did alot of research into the fuel mileage issue. While there are exceptions it seems, the general rule seems to be the newer the diesel the less fuel economy probability. This occured because of emission restrictions increasing each year. I had a 03 cummins, which would not get the mileage that some of the prior models would get, but better than alot of the newer years. Be careful with what others are claiming for mileage, there are a few out there that like to claim at least a couple mpg’s higher than they are actually getting. The other problem is some only going by the mpg’s that are being displayed on the computer. Hand calculated mileage can vary several mpg different than what is displayed on the computer. For my truck when they came out with ultra low sulfur diesel, the computer all of sudden indicated 2-4 mpg’s better than I was actually getting.

Again results vary, just consider the source and what seems logical. I agree your truck should do better, and one truck to the next there can be a big difference, even if they are the same year, make, model etc.

Chris Tuckner took the words out of my mouth. I would love to own a diesel, great power, great pulling torque…But they arent as feasible as everyone seems to think. About 7 out of every 10 HD pickups you see on the road are diesels, but Im not sure why. Maintenance is killer on these things, and now the gas engines have the same 100k mile warranty. At about 8k extra out the door for the diesel, Ill stick with my gas engines.

Cal, In the winter you are always going to get less because it takes more diesel to warm the motors up but in the summer it should be consistant. Watch where you put diesel in. I noticed that with mine the mileage would vary based off of where I fueled up. Hense the ULSD and Soy diesel. Now most all places are carring the ULSD and all diesel in MN is blended 10% soy. The blending took my milage down as well. Get the intake and exhaust opened up. It will get better mileage. I ended up trading mine 2 weeks ago for a gas. I miss it a ton but when I had it I was averaging 18-19 in the summer and 15-16 in the winter. You will not get anything better then around 18. The guys that are saying that they are getting 20+ are far and few between, although I have seen it. What happens when you fuel with diesel is that it is very foamy and you don’t always get the tank filed to the same level everytime you fill. So you need to be consistant if checking the mileage when re-fueling. Don’t rely on the number in the dash. If you can get to 18 you should be happy.

As far as the gas I was told the same thing that most guys with their F150 5.4 were getting around 18. I have yet to see that in 4 tanks of fuel. Averaging 16.5, I don’t know what I am doing wrong? I bought the truck used so maybe there needs to a tune up?

Have to agree with TazTyke. Where you buy fuel makes a world of difference. I have a 7.3 4X4 03 crew cab dually I average 14.5 all around mileage, pulling boat, horse trailer, running empty. Want to buy fuel where they sell alot of it, like truck stops. The worst mileage I ever got was from Cenex, my mileage dropped to 8 mpg on that tank I haven`t been back there since.

Like Tuck said the big advantage with the deisel is if you pull a lot. My old Dodge V10 pulling the horse trailer or boat ran 6mpg to 8mpg on the interstate. Could not pass a gas station.

All of my MPG calculations are done by hand, i reset the trip meter after every tank. I also am getting fuel at either Holidays stores or truck stops in Rogers. My tires are 265/75/16, I see these tires on about 80-90% of the diesels right now. The only other thing is I have custom wheels on the truck but that shouldn’t cause 2 mpg less in gas mileage average!!!

Thanks for the replies, I think I am going to call my dealer and see if there is anything I can do!!

I have an 01 D-max. I put custum rims on with 265/75/16’s. I pulled my uncles 17.5 foot Crestliner Fish hawk From Hastings to lake vermillion and back on one tank of fuel. I had the truck loaded with my things and his boat.I hand calculated it it and I got 18.5 mpg. Not to mention I drove into town twice on the same tank of fuel. In the end it was about 600 miles before I filled it up again. And I am still getting the same fuel mileage. Love the truck and don’t mind the little bit of extra maintence. Especially when you hook up and haul.

I feel the same way Duramax_2001 does. I love my oilburner!!
Not that much more maint. 5 extra qts. of oil but 2K more miles on a oil change and a fuel filter every 10K? Engines last longer too? I always put in 16 oz. of TCW3 2 cycle oil in a tank of fuel for the low sulfer. Also buy my fuel at Flying J, they turn over a lot of fuel and you get reward points. You will get lower mpg in the winter because of the blended fuel.
I just love the power and low end torque…

I would suggest superchips or taking it into the dealership and have them set your computer for better fuel economy. Superships offers several settings for fuel economy, power and such. I’ve got a 2004 Dodge Ram 3500 with the Cummins turbo diesel. I get about 21/22 miles per gallon on the highway and towing get 19/20 mpg. I took it into my dealership and had it set for the best fuel economy for towing. Prior to this I was getting around 14 mpg. Diesels seem to respond very well to superchips or reprogramming.

Jason

My fuel light came on my ’02 7.3L tonight and the odometer read 452 miles. I am not sure how big my tank is, but I know that it is sitting in my driveway until I can fill her up on payday. Those miles were all put on last weekend running in the cities without a load. How big is a tank on an F-350 Super Duty crew cab short box? I am sure glad I have a 4 banger cavalier to drive to work everyday.

Doesn’t your rear end have alot of impact on mileage, could it be your year end is geared for low end tourque? I have talked to a few guys at work who drive desiels and this seems to be the prevailing wisdom with them regarding mileage with a desiel or any other gas truck

26-27 gallons

Cal. Add 5 mile to every 100 you go for the difference in tire size. Also. Invest in a chip, either Super Chip or Edge. I added a Edge chip, set it on either 60 or 70 horse and raised my fuel mileage 2-3 mpg. Also a K&N air filter helps. I get 15 -17 pulling my 21 foot Ranger to the river and back. 16.5 average going up north with the air running. The power of having a chip is also great. No lugging or down shifting on hills.

Have your favorite mechanic check the computer setting for the fuel delivery, also, damman made a most excellent point on oil. I grew up on the farm, JD diesels, where fuel is claculated by gallons per hour. Weight of oil can make a hugh difference. Always use the lightest weight of oil you can for the job your most often doing. You’ll get better engine lubrication, = lower engine wear too. Try several and watch closely.

And on a side note, Mr. Tucker, how the heck do you get 18 with your 150 5.4? Did you do the super chip or what?

What about the warranty when it comes to adding a super chip? I heard that most Chevy dealers can detect if a chip has been placed in and backed out once you take it in for service. If you modify the stock engine it voids your warranty!!!

600 miles on one tank of gas…..Holy crap how big is your tank…40 gallons or what!!! Wow!!!

Calvin, Dodge also states any alteration of a Cummings engine, will void warranty. It is worded that it could potentially, I have yet to void any of my customers warrantys, although it would be easy. There is a connection they make, that they break a seal on a connector, therefore voiding it. This is just at my store though, I always recommend they wait until after their warranty is up, 5 years or 100,000 before chipping them. Most put them on, and remove them before bringing into the dealership for service.

big g

Well I called the dealer and they think since I have custom wheels I am losing about 2+ mpg on the average per tank! They also said with the bigger tires that my mileage may actually be a bit less than actual….Which is good for warranty I guess, but confusing to me….Something about the odometer reading slower cause the speedometer is off by 3mph or so!!!

They also said, to chip the truck if you want. If the chip causes any breakdown within the motor the warranty is voided, however if the chip doesn’t cause the breakdown its all good!!!

So I guess the questions is which super chip now….

I have heard some good things about the edge….

Calvin, I would be clear with the dealer, are they saying internal engine ? The most obvious thing will be pumps, and injectors. Chips increase horsepower, by increasing pressures, which can cause injectors to fail,leakdown etc. Make sure they will cover them as I know Cummings injectors are about $800 each Also, with bigger wheels, your truck is traveling farther than the odometer is showing, hance you are going more miles per gallon than is registering on your odom. You would have to know the OD of the stock tire vs. the specialty wheel to compute this. EDGE is a good product, alot of my diesel owners swear by them.

big g

Here’s a tire dia. conversion.

http://www.4lo.com/calc/gearspeedo.htm

Calvin,
By increasing your tire size you have in effect increased your gear ratio and decreased the efficiency of your motor. You now have a taller tire with a larger circumference, which will travel a slighty greater distance per axle revolution than with the stock tires. The engine has to work harder to turn the bigger tires and your rpm’s will drop lower than the desired range for optimum power. So you have a few choices, either change your differential gears, boost the horsepower, or live with what you have because you like the bigger tires. It is possible to reprogram the speedometer in some vehicles to have accurate speed & mileage. I wouldn’t chip a motor until the warranty is off unless your independently wealthy.

I guess I am going to have to live with what my mileage is on the diesel for now!!! Until either the warranty runs out or I can afford a Edge chip!!
Thanks for all the input guys!!!

If you had a handheld gps you could figure out how far your odometer is off. I did it on my old truck when I put larger tires on. As it turned out every 18 miles I could add a mile. Then when calculating my mileage it improved it my 1 or 2 mpg.

Jason

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And on a side note, Mr. Tucker, how the heck do you get 18 with your 150 5.4? Did you do the super chip or what?

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I have 32k miles on an ’06. I watch and log my mileage religiously. 18.5 tends to be the number I come up with the most when I do my math. Towing it drops a few obviously. I get better mileage with the ’06 than I did with the 01. And the 06 has an extra valve per cylinder.
Even the sticker says 14-18 MPG.

I’ve an 05 Duramax as well, but running 285’s, I wasn’t happy with my mileage stock either. 2000 rpm seems to be the break point of where the mileage seems to drop off. Check out dieselplace for a lot more info.
I bought a Bully Dog programmer. Huge difference! much more drivable, and better mpg’s! can adjust for tire size… This programmer is not noticable, as it plugs in for download, and then can be unplugged and put away. once you choose a setting, if you need to bring it, remove the program, and put it back to stock program.
What sold me was milage improvement, I borrowed a friends bully dog programmer to try before I bought mine, I drove to central Iowa, about a 3 hour drive. I was running 78-79 mph on Performance setting, and filled up when I got there. hand calculated 19.9 mpg…
This spring I put on an air intake and 4″ exhaust
Love it!

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If you had a handheld gps you could figure out how far your odometer is off. I did it on my old truck when I put larger tires on. As it turned out every 18 miles I could add a mile. Then when calculating my mileage it improved it my 1 or 2 mpg.

Jason

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I run a 3600IGPS on the dash of my truck to get accurate mph, my speedometer is off by about 3-4 mph consistantly!

I tried that bullydog chip and I thought my transmission was going to drop out of the truck, it shifts super hard, and puts out a huge black cloud of exhaust!!!
I didn’t like how hard the transmission clunked into gear with the bullydog, that would void the warranty instantly!! Maybe it wasn’t set on the right settigs! I will look into this more!!
Thanks again guys!

Ok just filled up this morning…. 363.9 miles and put in 22.08 gallons… Now all of a sudden I am getting 16.48 mpg!!! I put most of these miles on the hwy running over 70 mph, and about 2100-2200 rpm’s!!!!

Interesting!!!!