How To Improve 6.0 Gas Mileage?

390pi · August 7, 2008

It is funny:

The 6.0's mileage is not much better than my 8.1 w/ 3.73s: 10/town; 16hwy at 65mph.

I do nothing special to get that mileage.

Towing 10,000 gets me 7.0-7.2mpg.

cramer28 · August 7, 2008

ok I hope someone here can help me, I just bought a 2008 silverado 2500 hd cc 6.0L, three days after buying it I went to Les shwab and looked at tires they talked me into getting a 4 inch lift with 20 inch wheels 33 inch tires. so of course i went for it, truck looks good but i have lost a huge amount of mileage. I screwed up and put cheap am pm gas in it for three weeks i was only getting 7.4 mpg and towing a 27' trailer i got 6.9 mpg, i changed to chevron gas and got 9.6-10 mpg towing the trailer, and in town i get 8.2 driving with out the trailer. Les shwab told me which i asked them several times how many mpg i would loose they said 1-2 and thats it. We also bought a pro comp to adjust for the tires being bigger. But today im only getting 8.2 does anyone have any ideas of what to do...should les shwab be at fault for lying to me about the major loss of mpg?

2000DV4.8 · August 7, 2008

ok I hope someone here can help me, I just bought a 2008 silverado 2500 hd cc 6.0L, three days after buying it I went to Les shwab and looked at tires they talked me into getting a 4 inch lift with 20 inch wheels 33 inch tires. so of course i went for it, truck looks good but i have lost a huge amount of mileage. I screwed up and put cheap am pm gas in it for three weeks i was only getting 7.4 mpg and towing a 27' trailer i got 6.9 mpg, i changed to chevron gas and got 9.6-10 mpg towing the trailer, and in town i get 8.2 driving with out the trailer. Les shwab told me which i asked them several times how many mpg i would loose they said 1-2 and thats it. We also bought a pro comp to adjust for the tires being bigger. But today im only getting 8.2 does anyone have any ideas of what to do...should les shwab be at fault for lying to me about the major loss of mpg?

What size tires did you get?

Your speedo/odometer could be way off.

Griffin86 · August 7, 2008

ok I hope someone here can help me, I just bought a 2008 silverado 2500 hd cc 6.0L, three days after buying it I went to Les shwab and looked at tires they talked me into getting a 4 inch lift with 20 inch wheels 33 inch tires. so of course i went for it, truck looks good but i have lost a huge amount of mileage. I screwed up and put cheap am pm gas in it for three weeks i was only getting 7.4 mpg and towing a 27' trailer i got 6.9 mpg, i changed to chevron gas and got 9.6-10 mpg towing the trailer, and in town i get 8.2 driving with out the trailer. Les shwab told me which i asked them several times how many mpg i would loose they said 1-2 and thats it. We also bought a pro comp to adjust for the tires being bigger. But today im only getting 8.2 does anyone have any ideas of what to do...should les shwab be at fault for lying to me about the major loss of mpg?

What size tires did you get?

Your speedo/odometer could be way off.

+1 My tires were out by 10% even after my dealership bumped them up to the largest size. Now I get 17 mpg*

*Imperial Gallons

HDdave · August 9, 2008

I have a diablo sport tuner, true duals, and a cold air with 4:10's and 285's and I have been getting right around 13 average city or highway. My best advice is ditch the 6.0 and go with an lb7 d-max. My dad has a hypertech in his and hes getting 20 city and 24-26 highway hand calculated ( its a 4wd ccsb).

Billy-Jean · August 9, 2008

Alright guys help me out here. I have an 04 GMC Sierra 2500HD, Ext cab, 4wd,285 tires, 6.0/4.10 and I am getting 10-12 mpg. I know they don't get good but I was hoping for 14. I am not what I would consider a lead foot, so what can I do? I don't want to spend a ton of money, before I do that I will just trade it in on a new 5.3. Thanks in advance.

GM lost 25% of its stock shares then recovered. They did so by being greedy.

Didn't spend any money on Research and Development.

If GM makes a truck that gets 25 mpg, then i'll buy it, for now i wait

elcaminoman · August 29, 2008

I have a 69 ElCamino SS with a 6.5 (396) that gets a whopping 6 MPG and I am thinking of installing the new 6.0L in it just to get 13MPG. But that's why I have my 07 2500 HD for a daily driver. 13-16 is better than 6 anyday.

We need pics of both the ElCamino, and the truck. What exactly did you to to the ElCo?

The Elcamino is .060 over , so running about 408 cubes right now. Dyno at 425 h/p with 515 ft/lbs torque. Not a daily driver by any means, but with 40 series flowmasters you can here it coming. Setting off rice burner car alarm cruising through the parking lots. Pictures will be coming up when I get back to the states. Deployed for the military right now to a place where the sun shines everyday and a joyous 116 degrees during the day. But the gas is cheap here!

Billdog350 · September 8, 2008

Back to what the original thread was about, there are a few things you can do to increase fuel economy. Firstly, a tall, narrow highway rib tire with proper inflation pressure and a K&N or similar air filter.

Secondly, a custom PCM tune which: recalibrates your speedometer for the taller tires, optimizes your part throttle fueling (clean up the long term fuel trims to +-3%) for the air filter, increases your spark to an optimal level for fuel economy (as much as 20 deg over stock!), and drops your "normal" shift speeds a few mph as well as engaging your torque converter lock in lower gears and holding gears longer before downshifting. I keep my tow haul mode closer to stock settings so when I need to tow trailers or drive aggressively, the truck responds.

I use EFI Live for custom tuning on my 2003 6.0L 2500HD 4x4 ecsb which usually has about 1200lbs of tools and fluids in the bed and I was able to get 18+mpg on back roads (50mph) in VT with my tune. Highway economy is around 15-16mpg at 62mph (DIC indicated and verified) but drops to 14-15mpg at 70mph and 13-14mpg at 75mph!

So, in closing, keeping your speeds down on the highway (below 65 is optimal even though many of us hate to go that slow), get a custom "hands on" tune, and get rid of those aggressive mud-snow tires and get some highway rib style ones with lower rolling resistance.

Poker · December 20, 2009

Well guys I own a 2003 GMC 2500HD 6.0L and get 13-14mpg on the hiway

I drive a company truck which is a 2003 F250 superduty 5.4L does 10-12mpg

Got a few coments to make GMC rides better is more comfortable has unbelieveble amounts of power compaired to the Ford and better fuel milage. Driving both of these vehicles being as close to compairing apples to apples as it gets my GMC wins hands down as if it were a rigged compitition from the word go.

road_dog · January 5, 2010

There is nothing wrong with complaining about the fuel economy of a vehicle or at least discussing it if there is a large discrepancy between what the manufacturer states to be the estimated fuel economy range, or when the fuel economies of similar vehicles rank significantly better. In the case of the 2500hd, I'm not sure if the manufacture's ratings are inline with what the "street performance" is. Besides with all the tire modifications that people are doing to their trucks these days it becomes a very confusing topic.

It would seem that 14mpg is about the going rate on the 6L 2500hd with regular tires on the highway (unloaded). Loaded it will get closer to 10.

And so... with the current cost of gas I thought that it would be more economical to buy a second vehicle that I use for times when I don't need to haul anything. I thought that it might be a good idea. It divides the mileage I would normally put on the truck and puts some of it over to my new car. I figured that over the course of a year I would save myself around $3000.00 in fuel costs with having a car that is ultra efficient ~40mpg.

However add the cost of insuring another vehicle ($1000.00), the depreciation on the new car (around $2500.00/year), the $1000.00 in getting winter tires for it and I'm beginning to realize that it really wasn't that much cheaper at all. Besides my driveway is now full and I have the extra $ tied up owning another vehicle!

There is a silver lining of course and that is I don't feel as bad anymore about driving the truck everywhere I go and I have cut my fuel consumption by some 500+ gallons of gas/year!

Keepontrying · January 6, 2010

not sure this helps, but on my new 09 with 3.73s, i got 14.1 milking it at about 65 mph. I soon as i get in town it drops like a rock. I had an 06 mega cab with the hemi and 4.11s. started at about 14 and after 10,000 miles or so, could get 17 on a flat high way. Loved the truck, hated the service.

I am hoping that after this one breaks in I can get up to in th e16 on the highway. i can say it does run like a beast!!!!!!!!! I plan on changing to mobil 1 around 5000 miles. I like to run dino for the first change to let the valves and rings seat.

davzog · January 6, 2010

ok I hope someone here can help me, I just bought a 2008 silverado 2500 hd cc 6.0L, three days after buying it I went to Les shwab and looked at tires they talked me into getting a 4 inch lift with 20 inch wheels 33 inch tires. so of course i went for it, truck looks good but i have lost a huge amount of mileage. I screwed up and put cheap am pm gas in it for three weeks i was only getting 7.4 mpg and towing a 27' trailer i got 6.9 mpg, i changed to chevron gas and got 9.6-10 mpg towing the trailer, and in town i get 8.2 driving with out the trailer. Les shwab told me which i asked them several times how many mpg i would loose they said 1-2 and thats it. We also bought a pro comp to adjust for the tires being bigger. But today im only getting 8.2 does anyone have any ideas of what to do...should les shwab be at fault for lying to me about the major loss of mpg?

Anytime you go to a larger tire, you will give up a little mpg for two reasons....you have added a little unsprung weight which is the worst kind, and you have increased your rolling resistance, effective raising your final drive ratio....if you had a 4.10 rear end you probably are running somewhere around 3.80 or so with the 33s. I am sure you have noticed that you lost some performance with the tire change as well as the mpg.

I doubt that Les Shwab is "at fault" (I have no idea who he is), he really did not lie, but he was probably a little optimistic...plus it depends on your driving style. He told you there would be a decrease in mpg, but without a crystal ball there is no way to know for sure....actually, I am surprised you lost as much as you did....most of us don't drop 4+ mpg with 33s. In fact, I have a friend running 37s and he swears he get 10 mpg on the city and almost 12 on the hiway.

A couple of guys in our car club changed rear end gears when they went to larger tires and they got back their performance and even some of the lost mpg, sind they gained back some of the lost mechanical advantage from the larger tires.

I have 265x70x17s which are about 30" and lost mpg and power. I plan on lifting it in the spring and going to 33s also....I fully intend to change the 4.10 gears to 4.56 or so for the exact reason you are having these issues. I switched fron the factory 245x75x16s an lost about 1 mpg....going to 33s I expect to lose another 1-1.5 mpg...so 2-3 total loss.

Putting it into perspective, uf your truck originally got 25 mpg, a 4 mpg loss is nothing....but when you have a 6.0 liter HD truck at 6000+ pounds, everything costs mpg. A friend put on a massive front grill guard and lost 2 mpg due to the weight. Another guy loses 4-5 mpg every winter when he puts on his snow plow.

Are you calculating your mpg correctly with the new tires? My increased tire diameter was 4% larger than stock...so, I check mpg by dividing the miles driven by the gallons used and multiply the result by 1.04....compensates for the larger tires...

It costs to play....but if the truck looks super and runs super, enjoy it.....post a few photos so we can all enjoy it!!

Rat4go · January 6, 2010

Lots of you have touched on it, but IF YOU HAVE TIRES THAT ARE NOT STOCK SIZE AND HAVE NOT RECALIBRATED YOUR SPEEDO/ODO, your MPG calculations and/or your DIC are WRONG and likely calculating lower than they should. Taller tires go further per rotation than shorter tires. Changing from stock 245's to 285's means you go about 7% further per rev. or said a different way, tires turn less revolutions for a given 'real' distance. Since the odo and speedo are basically rev counters, they will read LOWER with bigger tires. Less miles shown on odo than reality =less miles per gallon than reality.

Even if the tire rolling resistance was the same, the tire diameter alone would make a truck that got 13 mpg calculate out at ~12.15 due to the odo error.

If you don't have a GPS that has MPH on it, you can check your speedo by driving 60 mph (as indicated on the speedo) on the highway and use the mile markers and a stop watch to time how long it takes to go a mile. It should take exactly 60 seconds. If it takes less, you have bigger tires and have not had your speedo compensated properly.

As some have mentioned, wider tires usually have greater rolling resistance, too. Yes, bigger tires is a way of effectively lowering your axle ratio (if you have a 4.1 with 285/75-16's, it's almost like having a 3.73 with 245/75-16's), except that the 285's have more rolling resistance, especially if you went from stock highway rib tires to an on/off road tread.

Want better fuel economy when driving your 2500 gas motor truck? Don't carry 1000 lb of unnecessary crap in your truck, launch like there's an egg between your foot and the gas pedal, and don't go over about 60 mph.

Newer 6-speed trucks are better thanks to the gear ratios and other things...probably worth 2-3 mph for both city and highway, but I'm not sure anyone with a truck they own wants to take on a big payment only for 2-3 mpg.

davzog · January 6, 2010

What he said................

VortecMax · January 16, 2010

Maybe Im on crack here but my 6.0L with my camper on , gets 16mpg. I have a programer, cold air intake, exhaust, and MSD ignition. I never get any better than 17 mpg when its empty, worst I had was 12 mpg pulling hills with the camper in the box.