Gas Mileage

sic lsx · August 5, 2011

Just did stop non stop trip on a full tank. 2010 4x4 z71 3.42 gears on stock tires and stock tune. Only mods factory replacement k&n and ddynomax vt muffler. Going 70-75 we got 20.2mpg best I've seen. It was cruise most of the time unless someone was slowing me down

Next thing for The truck is a best cover

Carder09 · August 6, 2011

15 if im lucky and maybe 11-12 normal driving

Yeah, im with you there, ever since I moved to SC I've gotten horrible gas mileage. Was the same way in tn when cruising through to go to Texas, all the damn hilly terrain

Austin83 · August 18, 2011

2008 5.3 AFM 4WD 3:73. I can average over 20 mpg on the highway at 65 mph. I have spent a few years learning how to conserve the max amount of fuel while driving. I do a lot of coasting while going down hills, approaching lights/stop signs, and while cruising through parking lots. I practice what is called "egg driving". I pretend that there is an egg under my gas pedal. It was hard to break some bad habits, but it also becomes a game to see what kind of fuel mileage I can get. If I can coast enough I can help take the edge off of decreased fuel mileage while driving in the city.

MikeNH · August 28, 2011

I decided to top off my truck yesterday in case this storm knocks out power long term (seems like it won't now). I downloaded an app for my phone to log fuel mileage with the last fillup and though I only put 140 miles on before buying more gas, MPG for that period was 17. Mostly highway but the truck was driven hard those miles. Once I have some hard data I'll post it up in a couple months.

jfsedlacek · September 12, 2011

I've gotten 19.5 MPG average according to the DIC over 30k miles. Over the road I manually record tank fulls at 22+ MPG in flat states and 18 MPG in the mountains. And yes, wind matters. I lose about 2 MPG headed West versus East depending on wind and vehicle speed. Generally, I drive +5 over the speed limit until the CB warns me not to.

I got a 2010 GMC 1500 extended cab 6.5' bed with power everything, 5.3L, Z71 option, 3.08 diffs, 6 speed, factory All Terrain 18" wheels w/Brigs DATs, K&N air element and oil filter, dual batteries, 110VAC inverter, Linex spray on liner, hard tonnau, CB and long antenna. Usually carry 600-800 lbs in the bed including a winch that mounts front or back.

Surprisingly, 4WD operation didn't kill mileage. I've used it for 1,000's of miles from Prudoe Bay to the Rio Grande through snow, gravel, mud and low range off road crawling. Love the Eaton locking diff. I live in North East Ohio but don't plow with it, this is not the right vehicle for it.

Something else that matters is the engine oil. I measured, not guessed, 8% less mileage using conventional oil (dealer oil change, hey I had coupons) versus synthetic (Royal Purple). Surprised the heck out of me but the test period was 10k miles for conventional oil and 20k for synthetic. Syn costs more but lasts longer and if you buy in 5 gallon pails like I do it's just a small premium.

Tire pressure matters a lot as I keep them at 42 lbs, well within the tire mfg specs. Factory says 35 but I think that's to keep the ride softer. After 30k miles my tires are about 50% worn and nice and evenly. TPMS is a godsend.

As you can guess I'm impressed by the truck.

One fun fact, my 2004 GMC work truck regular cab long bed with 4.3L, 4 speed, 3.42 RWD, and no power anything gets about the same mileage unloaded. That's over 122k miles. And as anyone with a 4.3L truck can testify, it's a dog. Technology marches on.

robkleinpeter · September 15, 2011

Hello. I have a 2006 GMC K1500 Crew Cab, 48,500 miles, 5.3L Gas/E85, 3.73, original tires. Ever since I can remember it averaged 15.6 MPG but after resetting the DIC several weeks and around 200 miles ago it's around 12.8 with 75% city -30% hwy. What's odd is just this morning the average was dropping wile idling at a red light incrementally to 12.1 and then increased to about 13 during acceleration. No noticeable engine problems and the only part I've changed was the EVAP vent valve solenoid. Does this sound right?

Wolfmansbrudda · September 15, 2011

I have an '07, K1500 Extended Cab 5.3L 4WD and average about 19.2 mpgs overall. On my commute (which makes up 90% of my overall driving), 20% is full expressway, and the other 80% is double-yellow-line regular highway with a few stoplights here and there. I also drive like your great grandfather. Very happy with my truck. My previous post on page was made just after I got the truck and was inaccurate.

jfsedlacek · September 15, 2011

Hello. I have a 2006 GMC K1500 Crew Cab, 48,500 miles, 5.3L Gas/E85, 3.73, original tires. Ever since I can remember it averaged 15.6 MPG but after resetting the DIC several weeks and around 200 miles ago it's around 12.8 with 75% city -30% hwy. What's odd is just this morning the average was dropping wile idling at a red light incrementally to 12.1 and then increased to about 13 during acceleration. No noticeable engine problems and the only part I've changed was the EVAP vent valve solenoid. Does this sound right?

Rob, I'm sure it has to do with the algorithm used to compute the average mileage. When mine was new it did vary a lot until it had a couple of thousand on the odometer. I don't recall looking at the average that often early on but I do remember it fluctuating. Measure it manually the next fill up to confirm it's in the 15MPG ballpark and not something else wrong. If it's OK, then give some time to get enough data to compute a better average.

I found the DIC average mileage figure to be close over time but no substitute for manual tracking.

possin08 · September 20, 2011

I have and 07 Silverado Crew Cab LTZ and I get 14-15 mpg in the city and 20-21 on the highway going 70-75. I only use shell 93 octane (no ethanol) and that gas seems to give me the best mileage. Mods done to the truck include K&N cold air intake, Hypertech max energy tuner and Corsa exhaust. If i fill up with 87 from mobile or BP my gas mileage drops to 12 city 18 highway.

robkleinpeter · September 23, 2011

Thanks for the reply Jim. Possin08's post brought up something I have been wondering. Since my truck supports running E85, does the ECM make similar adjustments (like increase the amount of fuel) if I use E10 or does it see it as pure gasoline?

jfsedlacek · September 23, 2011

Thanks for the reply Jim. Possin08's post brought up something I have been wondering. Since my truck supports running E85, does the ECM make similar adjustments (like increase the amount of fuel) if I use E10 or does it see it as pure gasoline?

Yup, the ECM controls fuel/air mixture, spark timing and, in my truck, throttle position based on what you're burning. It does take a bit of time for the ECM to get used to a new fuel so give it a couple of tanks before drawing any conclusion.

I did notice a small drop in MPG and a significant drop in performance when using 84 octane gas in the Southwest this last winter. Everywhere else in the US, Alaska and Canada, 87 octane was just fine.

It's been noted in this forum that more alcohol, in the fuel, gets worse MPG. Alcohol can make more power in a motor but it takes a lot more fuel to do it. So unless E10/E85 is way cheaper the cost per mile is higher than gas.

One of the first computer programs I wrote in the 70's calculated the MPG and cost per mile. It turned out that got better cost per mile burning 93-96 octane in my '69 Chevelle with a 327 I built having 11.5:1 compression, Isky cam, Holley, Eldelbrock, Mallory, big heads, headers..... I was getting 8-13 MPG but they were really, really fun miles.

The current truck gets 16 to 20 cents per mile. The '69 Chevelle was 5 to 7 cents per mile but adjusted for 40 years of inflation it's about the same cost as the truck.

MikeNH · September 24, 2011

My data is not quite complete as I didn't fill up before leaving for this trip but I started using an app on my phone about a month ago and between 8/21 and 9/16 I drove 999 miles, fed the truck 79.031 gallons at an average price of $3.82/gallon (premium) netting me an average of 16.5 MPG (agrees with DIC for a total of $302.28. Or about $20 more than if I ran 87, assuming my average MPG was unchanged. That's a lot of gas.

PH-Wolf · October 4, 2011

I'm getting between 19.2-20.8mpg is my average. I drive mostly freeway an country roads, not much stop an go. I also drive with a very light foot, keeping the RPM at or under 2,000 when the transmission shifts. Dash display shows I average of 19.8mpg. Current mileage is 17,300, an I run Mobil 1 5w30. 2011 reg. Cab. Long bed, 4.3L V6(auto) with 3.23 gearing. I know the 4.8l and even the 5.3 with the right gearing/drive style can get the same as my 4.3L 6 Cylinder.

The great deal I got for this truck made this engine worth purchasing. Got it for $15.700.81 out the door, I just paid cash for it. The 4.8L wasn't going for less than $20,000 then all the fees an taxes, etc. Added on. That's why I chose the 4.3L v6, I saved thousands. Plus I no longer tow.

Had a 2006 Chevy 2500HD Crew cab, short bed 4x4 LT. A averaged mid 19's , roughly the same as my current truck, LOL.

Mizz · October 18, 2011

12.223mpg 60%highway/40%city in my new to me 2500hd extended cab with a 6.0L 4:10 gears 4wd 106k miles. Terrain here is extremely hilly and curvy, 900ft elevation. I am hoping for better, just changed the oil, fuel filter, air filter and cleaned the MAF sensor. A buddy of mine has the same truck except with the 8.1L and he swears he gets 13-15 city.

rdnkcpa · October 19, 2011

2004 Silvy 1500 4X4 5.3L V8, 4 Speed Auto, 3.73 Rear. 123,000 Miles on truck, replaced heads at 119.

I get 16.2 to 16.8. The best the truck ever got was 18. When I switched from the factory Goodyear tires to Bridgestone Revo's MPG dropped 1MPG immediately.