GM owners ????

[Delaine and Lindy]

I have owned our 2008 since Nov 08. My question do you notice when the Regen process begins. I have only noticed it one time when I had less than 500 miles on the OD. Then I just could tell a little difference in the sound of the Engine. My Mpg stays about the same 10 to 11.5 Mpg 60 Mph. As we pull a heavy load. We have put very few miles on the Truck this trip due to Delaine driving her car down. But next trip we will not bring the car. GBY....

[exav8tr]

Lindy, I have just turned over 20k on my '08, which we bought in April of '08, and I can honestly say I have never noticed a regen process. As we travel around this area, unhooked, we are getting 13.9 MPG on the DIC. Hope it gets better soon.....Towing was around 11.4-11.8.

[Jolu]

My 08 is like Phil said. I have not noticed a regen. Most of my driving is pulling. I have been running around town for the past 6 weeks and have not noticed a regen cycle. So, I don't know if it has happened or not.
My mileage is about like Phils mileage with under 10,000 miles on the truck. JB

[TAKPAK]

I have had my GMC Duramax for just exactly one year this month, and it now has 12,500 miles on it. It's a 2008 K3500 (one ton) unit. When I first got it, the regen was noticeable, in that the pitch of the engine changed a bit, and the RPM on the tach would go up about 200 RPM. The biggest scare, at first, was the first four times it went into regen, the blue/grey smoke would come billowing out of the tailpipe for a while. Spooked me, in that I thought the turbo had blown a seal. I checked with the dealer, and he said that the smoke was normal, especially when new. After the first oil change at 6000 miles, it only happened once more, and hasn't happened since. Might have been some bad fuel in the beginning too. Now, once in a while, I can tell it's in regen, just from the RPM going up a bit, but otherwise, it goes unnoticed. My milage, empty on the open road ranges around 21 to 22 MPG. In town, it ranges 15 to 18, depending on the weight of my foot. Towing the 3400, it gets between 11 and 12. NO modifications have been made to the truck thus far, and I don't plan to make any. "If it ain't broke, don't fix it" as the saying goes.

[Delaine and Lindy]

TAKPAK, that is some awesome fuel mileage, I have never gotten that kind of mileage with a 1 ton 3500HD. If I were you I wouldn't let no GM tech change any settings at all. We have the Chevy 3500HD and have about 15,000 miles and it was a year old in Nov 2008. Have only had one issue and it was the drivers set, a bracket had to be replaced. GBY....

[MacDR50]

I can't say I have noticed Regen with about 1500 miles on truck. My mileage stinks. 10-12 in stop and go city and no better than 14 in highway driving. I intend to take it for a good run this weekend to see if it does better. If it doesn't improve it is back into the dealer. I have given up trying to make sense of mileage claims as they have such a wide variation

[exav8tr]

Roger, Please post your results when finished. AND if you take it to the dealer to possibly change something for better mileage or trade it for something else??? Not sure what the dealer could do. I used to be told "What you get is what you get". Is there something they can do????

[The Old Fogies]

We have a '05 2500 GMC. I get between 18 to 17 driving th work and around 11.5 towing. That is if I keep teh speen around 60 - 65. I not sure what the regen your talking about is.

[MacDR50]

I will post results and and, if applicable, what the dealer has to say.

[goin2themountains]

Roger. We've had 3 Duramax's in the family since my '04. None of them got optimum mileage until they had 15k miles or so on them. Just a thought.

[MacDR50]

Ok Results:
Distance Traveled: 530km (329m)
Mileage: 12.64l/100km (22.35 MPG/Imp Gal) (18.6 MPG/US Gal)

The DIC was dead on with my calculations on refill.

I also learned (sheepish smile) that the DIC is calibrated in US Gals when you select units to "English"

My lowest mileage since I bought the truck in Nov. was 27.5l/100km (10.3Imp or 8.6 US MPG.)
My best mileage prior to the long run was 22.3l/100km (12.7 Imp or 10.6 US MPG)

I drive 6km (3.7 miles) to work.
I did some research on the impact of air temperature and winter formulated fuel and I have the explanation below sums up what I suspected.

I am satisfied that the combination of my short trips in below freezing temps which do not allow the engine to warm-up properly combined with the lower energy output of winter fuel explain my lousy mileage. My long trip confirms that my truck doesn't need any work. I expect that warmer weather and summer fuel will improve the mileage.

The following was taken from the Louisiana DNR web site.

The primary differences between 1D and 2D fuel are the pour point and the viscosity. Pour point is the lowest temperature at which a liquid will flow. Viscosity is the resistance of a liquid to flow. A 1D fuel is designed for cold weather operation; thus, it is less viscous and has a lower pour point. A 2D fuel is used in warmer weather because it has a higher viscosity and pour point. The higher viscosity provides better lubrication qualities for the moving parts of the fuel injection system. Because 2D fuels contain more Btu's (British thermal units - the amount of heat necessary to raise one (1) pound of water one (1) degree fahrenheit) per gallon, they are able to deliver more power per gallon. This is critical to diesel engine fuel economy. The higher the Btu rating a diesel fuel has, the greater power yield per gallon; thus, higher mpg will result. Cetane rating is the diesel equivalent to gasoline's octane rating. Unlike an octane rating, which rates gasoline's resistance to spontaneous ignition, the cetane rating number (usually 40 to 55 for medium to high speed engines) notes the relative ease with which diesel fuel ignites. The higher the cetane number, the easier the fuel ignites; the higher the octane number, the more resistant the fuel is to ignition. Each manufacturer usually specifies a minimum or maximum cetane rating and the suggested operating temperature for 1D and 2D fuels. A given fuel may meet 1D or 2D specifications, but if the Btu rating is too low, then decreased fuel mpg will result.

[richfaa]

Guys we have the 08 Ford but the emissions and regeneration processes are the same. It can be very difficult to note that you are in regeneration. The Ford gives a MSG on the display console when regen starts and ends. We have a aftermarket guage installed that monitors all the trucks PC parameters including the pre turbo EGT.The EGT will increase by 400/500 degrees when it goes into regen so I can not miss the process and that is the best way to note that regen is taking place(high EGTtemps) The regen will last @20 mins and the MPG will decrease by @ 5 mpg during that time. Remember now..only applies on 07 and above trucks..earler trucks DO NOT REGENERATE.>

Look at your tailpipe. It should be clean that is not black and sooty like previous years..that is the entire point of the new standards.
a clean tailpipe indicates the DPF is working and regen is taking place.. You may not notice it but your truck is regenerating about every 300 miles....less if you can keep your EGT at 650 degees or better(passive regeneration) Lower MPG on these new generaton trucks is lower because, among other thing, the regen process is burning fuel that dos not turn the wheels. There is lot of goo info on the internet on this process.

[Jim Jarvis]

Further to what Rich said, a black tailpipe can also mean turbo trouble. I had the black tailpipe and thought I had regen trouble but that was not the case. Turned out the high speed turbo need replacing.

[Delaine and Lindy]

My mileage is about the same as my 2007 Chevy Classic (no DPF). However the HWY mileage is 1 mpg less one the 2008. The towing mileage is about the same. The DIC is right on the mark, as for fuel used and mileage. When I add fuel the amount is the same as fuel used on the DIC.

As for the tail pipe soot, I have none and haven't meet a GM owner who has had the Turbo problem... There sure could be some failures but I haven't meet them. I still don't care for the DPF system. I have always believed that the Diesel should be at the the least 5 minutes or more. But with the DPF system it just isn't a good idea. And I still believe that the DPF system a waste of Diesel. I would rather waste the Diesel by running the engine until the Turbo cools down. I do believe we will begin to see more Turbo problems. I don't believe in after market gadgets, I'm sure if they were needed they would be installed by the Manufactor. But if you think you need them thats fine with me. Good Luck. GBY...