14mpg+ Out Of 99-07 2500hd 4x4 6.0 Gas?

lcorrell · March 29, 2011

Anyone out there getting 14mpg or better out of 1999-2007 2500hd 4x4 with the 6.0 gasser? If so, what mods did it take to get there? I'm only interested in info on the HD models - I already know the non-HD models get significantly better mileage.

I bought a 2003 2500hd 4x4 ext cab long bed with the 6.0 gas last fall. It replaced a 1989 1500 4x4 ext cab long bed that had a warmed over 5.7 and got 14mpg driving back and forth to work and 17mpg highway (and had more power). I didn't research the 2500hd good enough and expected equivalent or better mileage out of the newer truck. I'm being thoroughly disappointed with the 10-11mpg that I am getting. I'm considering trying to trade down to a 1500 or to an older model truck to get better mileage. BUT, if I can do some things to this truck to get it to 14mpg or better I would rather do that and keep this truck. Probably cheaper than getting another truck too! At the mileage I'm putting on this truck at current gas prices even 13mpg will pay for $400 worth of mods within 6 months. So, is anyone getting 14+ and if so what did it take to get there?

[email protected] · March 29, 2011

Just fyi, they didn't make 2500hd's with 6.0l in them until 2001. And I actually get over 14 myself.

Stevens03 · March 29, 2011

Custom tune hands down will help. Also what size tires do you have installed?

lcorrell · March 29, 2011

I believe the truck is bone stock, but I don't know that for sure since the place I got it from couldn't tell me anything about the truck. It has the 4L80E auto trans, 261HD t-case, 4.10 gears, and 265/75/16 tires. I did notice the exhaust system is impressive, not sure if it might have been upgraded or not, but it has 3" duals (dual cats too) all the way back to the muffler, then right after the gigantic muffler it merges into a single 3.5" tail pipe. I believe I might have a cracked exhaust manifold on one side - any benefit to headers on these trucks?

[email protected] · March 29, 2011

What you're describing is the stock exhaust for the 2500hd models.

markw8 · March 29, 2011

More likely you have broken bolts rather than a cracked manifold. Your 265 tires might have hurt mileage a little. Mileage really suffers above 60 mph.

Mark

ATMINF · March 29, 2011

Get a custom tune. I get 16 on the Hwy. I have a custom tune from Charlie Wheatley and my truck is also a 2wd. Overall if you keep your speed at 70mph get a custom tune, and make sure the truck is in good working order 14-16 mpg on the hwy is doable. In the city 12-14 is the best.

Shatterz · March 29, 2011

Anyone out there getting 14mpg or better out of 1999-2007 2500hd 4x4 with the 6.0 gasser? If so, what mods did it take to get there? I'm only interested in info on the HD models - I already know the non-HD models get significantly better mileage.

I bought a 2003 2500hd 4x4 ext cab long bed with the 6.0 gas last fall. It replaced a 1989 1500 4x4 ext cab long bed that had a warmed over 5.7 and got 14mpg driving back and forth to work and 17mpg highway (and had more power). I didn't research the 2500hd good enough and expected equivalent or better mileage out of the newer truck. I'm being thoroughly disappointed with the 10-11mpg that I am getting. I'm considering trying to trade down to a 1500 or to an older model truck to get better mileage. BUT, if I can do some things to this truck to get it to 14mpg or better I would rather do that and keep this truck. Probably cheaper than getting another truck too! At the mileage I'm putting on this truck at current gas prices even 13mpg will pay for $400 worth of mods within 6 months. So, is anyone getting 14+ and if so what did it take to get there?

Before you start doing modifications (which almost never equal better MPG) and since you don't know the history of this truck, start off with a good round of maintainence. Change the air filter, fuel filter, new spark plugs, drop transmission pan and replace internal filter and get the transmission flushed, drain and refill transfer case as well. Also change front and rear diff fluid.

Take a look at your tire pressures, make sure they are correct and not low. See what you are hauling around and the truck with you and remove what you don't need.

This being a newer truck does not equal better MPG. Your 2500HD is significantly heavier than your 1500. You have a truck meant to work with a relatively low rear gear (4.10).

Performing the above mentoned items and perhaps a change in driving style if you drive more on the aggressive side, will yield you better results than any modifications and changes ever would, guaranteed.

cghbuilder86 · March 29, 2011

If you don't really need the 2500 I say trade for a 1500. Lots of nice ones around for sale I'm seeing. I know of a few people letting go of nice trucks just for gas.

hockeypro1411 · March 29, 2011

You're not going to see that great of mileage out of a 6.0. 12.5 is about average across the board, which isn't really that bad considering the weight of the truck. Your old 350 may have gotten better mileage, but it was also in a half-ton truck and a smaller motor. Being a newer motor means nothing. It's still ~13 ci bigger and makes SUBSTANTIALLY more power/torque.

Prokopchuk_9 · March 30, 2011

right now mine says 10.4 MPG average LOL

frdfandc · March 30, 2011

If you have an exhaust leak, that will affect fuel economy as well. Repair what is broken.

Also, replace the fuel filter, air filter and plugs. You can also do drive train fluids as well. Switching to high quality full synthetic oils in the differentials and transmission/t-case can yield a small improvement. Everything helps.

And considering IIRC, that the 2500HD trucks came originally equipped with 245 series tires, and yours has 265's on them, your calculations would be off.

A custom tune would help out as well with power, fuel economy, and if the tire programming is incorrect, this can be corrected as well.

lcorrell · March 30, 2011

Thanks for the input everyone.

First thing I do whenever I buy a new vehicle is go over everything and tune up what's needed. I had to rebuild the transfer case and the rearend on this one. It has new fuel and air filters, spark plugs look good, all new fluids. Right now, I can't go over 60mph because of a bad driveshaft vibration - that's not a big problem since the "highways" around here have a speed limit of 45. But I am trying to come up with a way to get it fixed - it seems no one does 5" diameter shafts and 1410 u-joints around here.

Actually the 350 in my old truck did make more power and torque than this 6.0 does. My understanding is that the 2003 6.0 was rated at 300hp and 360tq. The 350 in my old truck was based on the ZZ4 crate engine which was rated at like 330hp and 380tq! In the lighter 1500 truck that had a lot more get up and go than this truck and like I said before - better fuel mileage to boot. But the power level isn't my complaint on this truck - it's the fuel mileage. I don't currently have a NEED for the 2500HD, but I have a family of 6 and we like to do quite a bit of camping. It takes a pretty large camper to sleep 6 people confortably and we passed on some pretty good deals before because I didn't feel that I had enough truck to haul it around. So getting the HD truck opens up the possibility some day. Also been thinking about getting into a side business of rebuilding repairable vehicles and would like to have enough truck to haul a car hauler around comfortably. So, like I said, I would like to keep this truck, but 10-11 mpg just isn't acceptable.

The other problem I run into with the 1500 trucks is that it's really hard to find a long bed extended cab. It seems like they are all short beds and I really want the full bed. Then the fact that everybody seems to think their truck is gold plated right now based on the prices I keep finding!

I don't think my driving style is causing the poor fuel mileage on this truck. I tend to be one of those drivers that seems to get better mileage out of my vehicles than others. Like I said before I got 14/17 out of my old truck. I also get 15/19mpg out of our 1997 1500 suburban 4x4 (also a 5.7, but it's bone stock - much less power) and that's typically loaded with 6 people. I also get 13mpg out of my 450hp 1967 Pontiac Lemans and that's with my foot in the gas all the time!

[email protected] · March 30, 2011

right now mine says 10.4 MPG average LOL

Good lord man, you gotta stop doing those burnouts! Mine says 15.8mpg right now, but's that's because I quit using acetone and the weathers been cold and rainy lately.

V8MSY · March 31, 2011

right now mine says 10.4 MPG average LOL

Good lord man, you gotta stop doing those burnouts! Mine says 15.8mpg right now, but's that's because I quit using acetone and the weathers been cold and rainy lately.

Mine says 9.4mpg.

I've got new upstream O2 sensors being fitted tomorrow to see if that helps.