Quinlan

iTrader: (1)

I put over 100k miles on the exact truck, Long bed CC 4x4 about every 4th tank I would run 91 just for kicks. Never noticed any diff in milage. Always 10 mpg Towing 8mpg
Maybe I got 11 ONCE!! lol

pullmytrigger

I just checked the manual....

"Use regular unleaded gasoline rated at 87 octane or higher.............In addition , gasolines containing oxygenates, such as ethers and ethanol, and reformulated gasolines may be available in your area to contribute to clean air. General Motors recommends that you use these gasolines.

Sydwayz

iTrader: (1)

Wasting your money. Only run 87 in it; put 50K on mine and never anything higher. I was running a Hypertech and Predator tuner as well, changing tire size and torque curve; but left timing setting alone to stay with 87 octane. If you want, you could invest in an aftermarket tuner to retime the ignition for high octane rocket fuel.

wannabe

I use 87 in my Avalanche 2500 with the same 8.1. I have a Hypertech tune set for 87 octane, it gave me about 0.5 mpg and better throttle and more power above 4000 rpm. When towing my Chris Cat (11,000lb incl the trailer) I use 89 octane, just to give my self some extra oomph- the timing cuts back faster with a big load on 87.

Use the 87 for a while. Throw some Chevron Techron fuel injector cleanor in once and a while too.

Wannabe

Gimme Fuel

I have an 03 Avalanche 2500 with the 8.1L. Great engine. I have since re-tuned on chassis dyno using HP Tuners Software. Eliminated converters, 4" exhaust, 4" flowmaster muffler, cold air intake. I am tuned for 93 octane. Gained 2 mpg average and 60 hp.

If your engine is stock, you are fine. But if you are running a stock tune and have cold air and better exhaust, get it retuned! My truck on stock program for baseline was running a 15.7 AFR at WOT pull. That is waaaay lean. We did my friends HD with 8100 too, he was at 15.6 AFR on stock tune. I have a feeling that the motor he burned up at 60k after a heavy long distance tow was because of this lean condition. Rings were shot. Mine was using quite a bit of oil before my re-tune also. I have since sealed it up a bit better with break in additives and thicker oil. Running the thicker oil made it a lot happier and reduced temps. Mine could use a rebuild in the near future. Previous owner towed large enclosed trailers between MI and FL for 108k miles of its life. I rag the heck out of that engine and it keeps asking for more.....Next year it will see new rings, bearings, and 496 HO cam.

I have 4.10 gears and the 4L80E trans. If I keep it under 65 mph I can get between 15-17 mpg......towing around 8k 11-13 mpg. It all stinks above 65 mph with those gears...time for taller tires too I guess! I rarely drive big highways though.

wannabe

Under 65 I can get 14-15 mpg. But that makes me feel like I am being passed by the old ladies- LOL.

I get 13 mpg at 75 mph. Thats 2500 rpm with the 4.10 axle.

I have had my tuner since 2005, so I have most of the miles with it.

I get 8 mpg towing the Chris Cat.

I also use Mobil 1 Synthetic 10-30 in summer, 5-30 in winter.

Wannabe

Quinlan

iTrader: (1)

Dont forget a QT of Oil every 1500 miles.

blue99fbody

thats horrible advice if it calls for premium it needs premium. all my vehicals call for premium and thats what they get. knock sensors detect knock/detonation after it is already happening and trys to stop it. they dont prevent it. with that said im sure the 8.1 dont call for premium.

Gimme Fuel

I run 20-50 Mobil One. Motor sealed right up, nice oil pressures (had fluctuations when 10-30 syn got warm above 4k rpm). Power doesn' fall off as bad once it gets up to running temp (210*) like it did with the 10-30 syn. I still need a 170-180* thermostat in it. It makes a huge difference in mine and that is not part of the temperature dependent fuel curves wither. When I was doing sanctioned 300' timed sand drags with it, it was interesting how much my ET's dropped off once it got up to temp. Killed my bracket placements...haha.

Sydwayz

iTrader: (1)

Silly conversation to be having about fuel mileage on an 8.1L gas engine my friends!

There are dozens of variables which affect mileage. Heck, a bug deflector and oversized mirrors can cost you 1mpg; not to mention ratios, tire sizes, wheel sizes, and weights of each; stick vs. auto, 2wd vs. 4wd, lifted or lowered, mud flaps, running boards/nerf bars, bed cover, how much crap you carry daily; as well as individual driving style.

Say you magically pick up 2mpg. On truck with an 18 gallon tank... woohoo; you picked up 36 miles. Most tanks sizes are designed so the vehicle goes ~300 miles or so.