Denalis stopping while driving- class action suit?

[WalleyeMikeIII]

As far as Premium fuel, nothing in the owners manual that I can find, probably because the owners manual are more generic these days and often there are different engine options.

It is actually in there, at least in the 2022 model, see below.
I did note that from 2021 --> 2022 the recommended octane was dropped from 93 to 91, probably a marketing thing, since some states only require "premium" to be a minimum of 91 (perhaps elevation related), Minnesota, where I live, is one. I have found 2 stations in town that have 93 and Costco is 92 here. I have been running from Sinclar's 93, unless I am in a pinch on the road, where sometimes all I can find is 91, then I go with that, since it is all there is.

Note the advice is pretty "loose" in the OM. Says 91 is "recommended" but then says if you can't find premium, use 87 mininum. Then, under "prohibited fuels" it says any fuel that is not the recommended octane. Great documentation.

Net, I have never run less than 91, and mostlly 93 in mine..have shared this w/ friends, and they too have only run premium. Not sure if this will mitigate all the issues, but anything that eliminates knock has to help.

 

[jfoj]

@j91z28d1

The 6.2l is not Flex Fuel E85, the 5.3l used to be as I recall, the L84 5.3l is not showing as E85.

 

[jfoj]

@WalleyeMikeIII

I knew the 2024 owners manual was a bit skinny, it is over 100 pages less than what you posted, 142 pages and nothing other than how to put fuel in the tank.

 

[WalleyeMikeIII]

@WalleyeMikeIII

I knew the 2024 owners manual was a bit skinny, it is over 100 pages less than what you posted, 142 pages and nothing other than how to put fuel in the tank.

Full Manual available for download here

 

[tagexpcom]

I've used "Regular" (87 octane) in my 2021 Yukon Denali 6.2L a couple of times. First couple were before I read about the higher compression / engineering that makes "Premium" (90+ octane) strongly advised for proper running. I also found that I could not make it towing a trailer from Lakeview OR to Winnemucca NV (where there's only 1 gas station with "Regular" only) along the way without carrying 5gal of "Premium"!

The couple of times I used Regular I didn't have noticeable issues except a loss of power accelerating up a long 6% grade while towing... the rig topped out at ~60-65mph and wouldn't accelerate any more with foot-peddle all the way to the floor - which surprised me as this doesn't happen with Premium.

The engineering, higher compression ratio explanation + towing experience has pushed me into taking "Premium" recommendation seriously enough to carry that 5gal can to span the long distances without gas stations in the high dessert.

 

[jfoj]

Full Manual available for download here

Hey, I looked at what was included with the vehicle, never really worried about online manuals when I have the printed one!

Will be interested to see if the online manual is double the pages as the one included in the vehicle. Must have been another fuel saving idea?

Online manual is 288 pages more than the printed manual in the truck, go figure.

 

[jfoj]

@tagexpcom

Scary about the 6.2l WOT and topping out at 60-65 MPH. May be a factor of weight, wind resistance, elevation and grade?

But look back a bit earlier in this thread where I have the Load and Timing where the timing was retarded by like 30 degrees, this probably equates to like a 100 HP loss, unsure in Torque, I wonder if you were pushing into having the timing pulling 30 degrees like what I found. This would clearly be a reason the engine is topping out on top of all the other variables.

 

[WalleyeMikeIII]

Hey, I looked at what was included with the vehicle, never really worried about online manuals when I have the printed one!

Will be interested to see if the online manual is double the pages as the one included in the vehicle. Must have been another fuel saving idea?

Online manual is 288 pages more than the printed manual in the truck, go figure.

FWIW, the digital copy of the manual is also available on the infotainment screen in the MyGMC App...so, in a way they did give you a copy...it is 2025, after all The main reason I know about the electronic version is I ordered my vehicle, it was back when it was a long wait to get one...so in the meantime, I downloaded the online version and read it, while I was waiting on my vehicle to be built and arrive. I do like the electronic version, as you can search it, and it is hyperlinked...so makes navigating it a bit easier.

 

[tagexpcom]

@tagexpcom

Scary about the 6.2l WOT and topping out at 60-65 MPH. May be a factor of weight, wind resistance, elevation and grade?

But look back a bit earlier in this thread where I have the Load and Timing where the timing was retarded by like 30 degrees, this probably equates to like a 100 HP loss, unsure in Torque, I wonder if you were pushing into having the timing pulling 30 degrees like what I found. This would clearly be a reason the engine is topping out on top of all the other variables.

You're right - there was a significant (20?mph) headwind and it's a 5400lb cargo trailer - basically a square box and the drag greatly increases as the wind flow speeds up - so maybe 65mps + 20mph headwind is like trying to do 85mph and still accelerate? Was a steep (at least 6% grade), many mile uphill mountain road, likely 5000-6000ft elevation. In this area of Eastern Oregon....


I was surprised as I hadn't had this happen before with Premium - so I'm guessing it might have been the 87 Octane along with the wind and full 65mph and 6% grade tipping things over the edge? but I don't know for sure and don't plan to experiment.

 

[jfoj]

@tagexpcom

You were testing out the 6.2l for sure. It is crazy how a trailer is like pulling a sail down the road. Even on my 2005 6.0l pulling an small, empty enclosed trailer it killed the fuel economy on my 6.0l, was down to 10 MPG! I bet with 87 the thing was knocking up a storm and pulling timing.

I hope your 6.2l holds up. I would not be running 0W20 towing with one of these engines.

Would have been interesting to see what the engine oil temps were running.