Hey guys - another FNG here. New owner, first diesel...you've heard the story.

I have a million questions, but I'll start simple with this one: Once the low fuel light comes on, how far do I have before I'm truly out of diesel? I've owned vehicles ranging from 20 miles to 40 miles. How about my new '05 Duramax Crew Cab if I'm not towing anything? Also - I guess as long as I have your attention... How accurate is the truck's mpg gauge compared to actual mpg? I haven't had the chance to figure it out yet, I'm still on the first tank of diesel. FYI, I have averaged out to 17.3 on the truck's mpg gauge so far.

Thanks in advance - Awesome site! :ro)

The owners manual will actually tell you how much fuel is left when the light comes on.
Mileage, however, depends on your truck and driving habits. Usually you have about 3-4 gallons left depending on your tank size. Figure about 40-55 miles left.

that is going to vary with each truck..personally when my light comes on I know I have exactly 3 gallons left and with my driving style I can figure how many miles I have. I have a 26 gallon tank, but you may have a 34 since its a Crew..

Hey guys - another FNG here. New owner, first diesel...you've heard the story.

I have a million questions, but I'll start simple with this one: Once the low fuel light comes on, how far do I have before I'm truly out of diesel? I've owned vehicles ranging from 20 miles to 40 miles. How about my new '05 Duramax Crew Cab if I'm not towing anything? Also - I guess as long as I have your attention... How accurate is the truck's mpg gauge compared to actual mpg? I haven't had the chance to figure it out yet, I'm still on the first tank of diesel. FYI, I have averaged out to 17.3 on the truck's mpg gauge so far.

Thanks in advance - Awesome site! :ro)

Welcome to the DP. Diesel is a dirty fuel, I personally would not wait till my fuel light came on to get fuel, all the dirt from the bottom of the tank may cause problems for our already delicate injectors and you will risk clogging your fuel filter with debris. I generally fill up my tank (34 gals) before it gets to the 1/4 mark of the tank, plus it's not as painful ($$$$) when you fill up when you still have fuel in the tank. I would not trust the accuracy of the computer on these trucks, I'm sure they are off by a gallon or two, but that also depends on you're driving habits. Good luck.

Some people have reported running out of fuel just after the light comes on, so it is a risky proposition until you find out the hard way for your specific truck. Also remember the fuel is used to cool some of the electronics, so as the level gets low, so does the cooling capacity.

OCDUNE

The low fuel light came on while I was test driving my pickup and the computer said I had 19 miles left. The dealership filled it up before I left and I haven't let it get that low since then. Like thewad1 said, it doesn't hurt as much when you are only topping it off instead of filling it up.

Why test it. Fill up when you get at the one-half mark. Only idiots run out of fuel.

Running out of Diesel is more trouble than its worth. I wouldn't try it. Fill up at the one quarter left mark. The DIC mpg readings are somewhat overstated. It can be from .30 to 1.50 mpg off. On mine, the DIC would read 18.5 mpg when actually it was 17.8 mpg. Always hand calculate the mpg.

Thanks for the info! This morning I ran for 10miles after the light came on, then filled up. I was able to top off with 24.5 gallons of fuel. So, I'm guessing there was 1.5 gallons of diesel left in the bottom of the tank (26-gal tank). Have I dazzled you with my math skills yet? The DIC read an average of 17.5mpg. I don't know exactly how topped-off the truck was when I picked it up from the dealership, but my calculations have actual mpg close to 16. Hopefully that will get a little better as the truck breaks in.

Merk67, My DIC shows that I'm getting 16.0mpg, but my hand calculation i'm getting 18.0mpg and thats driving easy and I have 22,000 mi on the truck and no mods. Enjoy the hell out of the New Truck and welcome.

Welcome to the DP. Diesel is a dirty fuel, I personally would not wait till my fuel light came on to get fuel, all the dirt from the bottom of the tank
F.Y.I these trucks do NOT have a "floating" fuel pick up, they ALWAYS draw from the bottom...hate to bust your buble;)

[quote=thewad1] I generally fill up my tank (34 gals)quote]

Arent the tanks 26 gallons? When I got under my 2005 2500HD Crew Cab, there was a little sticker on the tank that said "26 gallons"...but I was surprised...I always thought the HD's had bigger tanks than that. Didnt the old GMT-400 Suburbans have like 42 gallon tanks?? ...maybe GM put the wrong tank in mine:mad:

---Ben

Long Bed CC have the 34 gal tank.

ahh ha! thanks

ive been 27 miles after my light came on and i only got 31.8 gallons back in the tank.fyi

Some people have reported running out of fuel just after the light comes on, so it is a risky proposition until you find out the hard way for your specific truck. Also remember the fuel is used to cool some of the electronics, so as the level gets low, so does the cooling capacity.

OCDUNE

Keep and eye on this, I had that problem on my old GMC 6.0. Took it back to the shop after it ran out a time or two to see the what the problem was. The low fuel warning would chime then it would run out. Not 30 miles, but more like 30 feet. The dealership fixed it by replacing the fuel pump in the tank. They said the fuel gauge was located in the pump. And the bad part was it was like 20 miles out of manufactors warrenty.Censored Extended warrenty covered it, but it still cost some. So now that I am off topic, If your light comes on it might be too late.