Last post on Dec 15, 2012 at 3:45 PM
You are in the Chevrolet Silverado & GMC Sierra
What is this discussion about?
Chevrolet Silverado 2500HD, Chevrolet Silverado 3500, GMC Sierra 2500HD, GMC Sierra 3500, Diesel, Fuel Efficiency (MPG), Truck
#609 of 620 Re: 2009 Duramax 2500 [nater37]
Sep 16, 2012 (11:45 am)
A lot of this kind of fuel mileage problem comes from the driving method. I believe your truck has a tachometer like my 2006. When you accelerate with a big load do not wind the engine to high, say 3000 to 3500, RPM for all it accomplishes is using lots of fuel. When I am towing I rarely let the RPM exceed 2000. When driving without a load I take the RPM at speeds under 35 to 2000 or so and after that take my time and keep the RPM below 1800. Think of it this way, that 6.6 liter engine is more than twice the cubic displacement of a 4 cylinder engine. 4 cylinders go to 3500 to 4000 RPM or more all the time for shifts. So divide that by 2 for the diesel and you get your target RPM ranges. I recently took a fishing trip with 21 ft boat loaded and the truck heavily loaded and made 24 mpg going up north and 22 mpg returning at faster speeds. Oh yes, these truck do not like being pushed to 65 or 75 while towing plus the trailer tires are usually rated for a Max speed of 55 to 65(look at the tire sidewall). I tow our big boat, 17,000 lbs at 13 feet high by 10 feet wide by 45 feet long triple axle, at highway speeds of 55 to 60 cruise and max downhill of 65mph. Doing that I get between 12 to 16 mpg depending on terrain.
#610 of 620 Re: 2009 Duramax 2500 [nater37]
Sep 17, 2012 (2:31 am)
I think that there are at least two things I would like to recommend as possible answers to your post.
The first thing is that your Duramax is not broken in yet and probably won't be for another 30K miles. Patience!
The second thing is that it seems to me that speed and MPG are inversely related. The faster you go after a certain point the worse the MPG.
About 6 weeks ago I drove to Winston Salem 150 mile drive and kept the speed on 62 mpg and got 20.2 mpg that was when my 06 Chev just turned 50K. Prior to that time I was getting 17.8 MPG after GM replaced the turbo. The new turbo (probably what you have and much better they told me) actually reduced MPG about 2 and that was back 1.5 years ago. The Chev got in the 20 range when new but not after the new turbo until 6 weeks back.
Some where you can find the power curve graph for OUR engine. See if you can drive where the power HP and Torque are at its maximum for a certain engine speed measured in revolutions per min. That number will be around 1750 RPM's and will be 60 and 65 miles per hour.
Keep driving and it will just get better but don't expect it before the engine is broken in.
Sep 17, 2012 (8:41 am)
Find the sweet spot for your engine. I have a 2005 and 1700RPM is where it likes to be. My wife has a heavy foot and she never gets good mileage from the diesel; so I keep her in the Geo Metro as much as possible.
#612 of 620 Sudden lose of mpg on 2007 Duramax 2500 HD
Oct 06, 2012 (4:02 pm)
I bought a 2007 Duramax a month ago and it was getting 15.9 mpg on trip home. I put the chip in it and my fuel dropped to 13.5 mpg. I pulled a small camper trailer approx. 400 miles and got 9.9 mpg. After I quit pulling trtailer just going back and forth to work I am still getting 9.9 mpg. That was with my H&S chip set on "Hot" and not getting into it. I have it turn completly off now to see what happens. I have new fuel filter. Truck has 20" rims & has 6" lift on it. Any suggestions?
#613 of 620 Re: Sudden lose of mpg on 2007 Duramax 2500 HD [rbboyd]
Oct 07, 2012 (1:24 pm)
How many miles and hours on the truck?? How wide is the tread patch on the ground of the tires? When you say "Chip" is it a controller with multiple programs or something that plugs into the data slot inside the cab? The units that plug in in the cab are notorious for causing permanent damage to the engines computers and to the engine components such as fuel injection system defaulting to maximum fuel or burning up the turbo or damaging engine sensors and since the program is no longer stock the trucks computers cannot tell you what went wrong! Last thing is Never, Ever tow with with any computer modification set to HOT since the engine will overheat in many ways that you can no longer know about due to the change in the computers. Good computers that work with the stock computers and do not change the warnings system or the gauge readouts cost quite a bit, on the order of $1500 to $2000, when installed properly. Anything cheaper are the ones that can cause significant damage to the truck. Do Not take it to a dealer, go to another shop that is qualified to work on the Duramax system for diagnosis.
#614 of 620 Re: Sudden lose of mpg on 2007 Duramax 2500 HD [kacansas06]
Oct 07, 2012 (6:29 pm)
I bought the truck with 84,000 miles on it and it now has 92,000 miles. The hours on engin has been reset. My tire size is 325x12.5x20. I pulled a small camper trailer approx. 400 miles but had my H&S chip set on mild. The H&S chip cost me $1,400 and was installed by a shop in Baton Rouge, LA. that does after market accesseries. It is one you can change on the fly. I am thinking that the shop didn't set the chip correct on fuel. BTW they told me to leave my chip set in the "HOT" setting at all times. The mechanic said I would get mpg because it had the most horse power provided I drived normal & not racing. I have the after market exaust & I put in the K&N air filter. The shop is suggesting the "Cold air Injection" instead. Any suggestions? thanks! I am working a pipeline around San Antonio till after the first of the year. If we rain out I will bring to a shop.
#615 of 620 Re: 2009 Duramax 2500 [coontie66]
Dec 03, 2012 (3:27 pm)
I have disagree with the break in part of the comment posted I was told when I purchased a new chevy duramax it would improve as it broke in as to date it has 99186 miles on it and has done nothing but get worse and gm for sure does not have a clue what is going on they will tell you a bunch of bs but no logical answers I started at 21 empty 14 towing a 16000 lb trailer now I am at15.9 to 16.3 at best empty and 10.2 towing my 1500 lb boat one reason I know is the fuel is not worth a crap and gm could give a damn less about so looks like we are on our own
#616 of 620 Re: 2009 Duramax 2500 [rajun55cajun]
Dec 03, 2012 (4:01 pm)
I agree with rajun55cajun. Break in of my engine seems to have made little difference in mpg. Tire size made the most difference. I replaced the stock summer tires with a wide all season that had a road contact width of 12" 1/3 greater than the stock after a year. MPG went down by at least 15% to 20%, 4 to 5 mpg. A year and a half later I changed back to a close to stock width of 8.5" and slightly larger diameter and recovered most my mileage loss. Since I have an '06 it is not built for todays 15ppm ultra low sulfur fuel and that has cost me about 2 mpg. So today I can still get into the mid 20's mpg unloaded at less than 60 mph but usually get about 21 to 22. Mixed in city driving is around 18 to 19 mpg. City only with no highway speeds I get 16 mpg. Living in MN I change tires for winter and that takes away another 2 mpg in the city and about 1 mpg highway. I was told by nearly every tuner manufacturer to never run the engine with a much higher than stock program for you may overheat the turbo and other exhaust components such as valves. I was told by many more people that own these to not try to push it to 65 or 75 mph when towing a trailer. My experience with the truck has taught me that 55 to 60 mph towing gets me better mileage and 75 drops it into the 6-8 mpg area which is less than half what the truck can get when towing. I will take 14 mpg towing 17,000 lbs over a little more speed which could ruin parts of the engine and transmission.
#617 of 620 Re: DURAMAX FUEL MILEAGE [exrench]
Dec 09, 2012 (10:27 pm)
I think you are going to be upset because I have a 2007 3500 dually with 373 gears in rear end it got 12.5 to 13.5 towing a 46 ft. gooseneck with living quarters and a race car which weighed about 16000 lbs that was new when it was at that and the older and more miles I put on it it got a lot worse I pulled a 2200 lb boat at 75 mpg from fla to sc last week and got 10.4 mpg so any body tells you they have to get broke in is blowing smoke because mine has 99689 miles on it and shows no codes or evidence of any thing being wrong I wish somebody had an answer because gm sure as hell don't and does not really care I bought this truck and it was supposed to be the best thing on the market but I surely have a different opinion about that and it seams nobody else has an answer either good luck
#618 of 620 Re: 2009 Duramax 2500 [kacansas06]
Dec 10, 2012 (7:02 am)
I have the same story with my 06Chevy 2500 diesel. Slow down , IT really does improve mileage.