Various Fuels in our 2007 6.2L L92

[donjetman]

I'll start by saying "I don't hot rod or tow". Stock factory tune.


The first yr we owned our 07 Denali (2019) we ran 87 octane and got a DIC knock sensor warning once. Then I ran 89 octane, and 91/93 on many hwy trips and determined gas mileage was:

15.5 on 87
16.5 on 89
17.5 on 91+

In July 2020 Swathdiver made this post: https://www.tahoeyukonforum.com/thr...eceonomy-5-3l-only.120104/page-3#post-1468328

about running mixes of unleaded with e85. I think e85 cleans. So for 6 mths I ran a 25% mix of 87 with E85 for 6 months. Ran great. No issues. Cost per mile was reduced. But the place I buy e85 at is 20 miles away and I don't get by there very often. Today, at this location, e85 cost about $3.00/gal, premium about $4.00/gal. These days, if I happen to be driving by this e85 location, I put 4 gals of e85 in then fill it the rest of the way with 87.

In April 2020 I Installed new 180* thermostat – Motorad# 523-180

From early 2021 until now I have been running premium unleaded.

In April 2022, at 174k miles, I changed all 4 O2 sensors and started running 0w-20 oil. Now I'm getting 19.0 mpg hwy and 16.0 mpg locally.

 

[gooffeyguy]

Lighter weight oil, easier to pump through the engine, less resistance

 

[Joseph Garcia]

I've used only Sunoco 93 octane in my 07 Yukon XL Denali. There is no E85 that I am aware of in my area, though I have not looked hard for it.

I got a Black Bear Performance tune shortly after purchasing the truck used, so I did not track my gas mileage prior to the tune. I don't tow to speak of (one 500 mile trip per year with a 1000 lb. trailer), but I do have a heavy foot during most of my driving.

City: 10-12 mpg
Highway: 15-16 mpg
Highway with my wife onboard: 18mpg (no heavy foot activity)

 

[jdwood1111]

I just posted in one of two threads but I had the exact same experience and almost mileage on my trip down and back to Florida! 15.5 on 89 and 17 on 91+. I have been looking for E85 but not readily available so haven’t tried that. I am running the Range AFM device though which lost me about 1mpg. I would love to leave the truck without the device but this forum has be too nervous to go back now!! I am exploring local options for tuning it out.

 

[B-train]

I have run everything from 85 octane (western USA), 87, 88, 91 (ethanol blend and eth free), and E85.

85 octane seems just fine in the mountains for some odd reason and I never saw a change between that and 87. Running 91 the motor seems more responsive, but not enough mpg improvement to justify the added cost per tank.

87, 91 (both types) pretty much the same mpg, premium is better on long trips after the engine relearns the fuel curve. Again, though the cost doesn't equal mpg increase benefit.

E85- truck not designed for it from the factory (I thought 2008 was.....oops) but I figured I'd try it since it was $1 less per gallon than 87 at the time. This thing ran like a freaking champ on E85!! Mileage was about 3 mpg less than what I got with 87, but man did it like the high octane fuel. I did end up having to clear lean bank codes because the injectors couldn't squirt enough fuel to keep the desired richness for the cats, but not really a big issue as far as I'm concerned.

Switched back to 87 and it ran great. It definitely cleaned up the cylinders with its cleaning properties. It was a fun little accidental test.

Regular 88 (15% eth) is my latest experiment to see what the cost value is by using more ethanol for higher octane, but less regular gas in the blend. Time will tell, but as of now it seems to like it just fine.

 

[Geotrash]

I have run everything from 85 octane (western USA), 87, 88, 91 (ethanol blend and eth free), and E85.

85 octane seems just fine in the mountains for some odd reason and I never saw a change between that and 87. Running 91 the motor seems more responsive, but not enough mpg improvement to justify the added cost per tank.

87, 91 (both types) pretty much the same mpg, premium is better on long trips after the engine relearns the fuel curve. Again, though the cost doesn't equal mpg increase benefit.

E85- truck not designed for it from the factory (I thought 2008 was.....oops) but I figured I'd try it since it was $1 less per gallon than 87 at the time. This thing ran like a freaking champ on E85!! Mileage was about 3 mpg less than what I got with 87, but man did it like the high octane fuel. I did end up having to clear lean bank codes because the injectors couldn't squirt enough fuel to keep the desired richness for the cats, but not really a big issue as far as I'm concerned.

Switched back to 87 and it ran great. It definitely cleaned up the cylinders with its cleaning properties. It was a fun little accidental test.

Regular 88 (15% eth) is my latest experiment to see what the cost value is by using more ethanol for higher octane, but less regular gas in the blend. Time will tell, but as of now it seems to like it just fine.

On the 6.2 it's not about the cost/benefit per gallon of fuel, but about the durability of the engine - especially under load. There have been numerous discussions here about this, and ample video evidence from engine teardowns on YouTube to support the case for premium on these. One of them, called 'I do Cars', says that he sees a ton of GM 6.2L engines with failed pistons from people running regular octane fuel in them. He said it's the leading cause of death for that engine, in his experience.

Now is about the time that all of the "But it has knock sensors to protect the engine!!!" people chime in. Yes, but it's not a perfect system, and there is only so much that it can do. So, the engine will still experience high levels of detonation of short to moderate duration. Detonation = exceptionally high internal cylinder pressures (ICP's). And like hitting an object with a sledge, you won't break it the first time, but keep it up and it will fail - especially aluminum because it accumulates fatigue.

 

[gooffeyguy]

The key thing to remember, knock sensors have to detect the problem before they can act on it, so the damage, even very minor, has already happened before corrective action has been taken.