NHTSA opens preliminary probe into more than 870,000 GM vehicles

[Jay P Wy]

Oh I have no doubts there is some contribution from low octane fuel. Pinging / Rod bearing taking a beating ? All of that makes sense.

Does the fuel door on these 6.2L vehicles have a warning not to use below 91 ? My 2014 challenger manual had a specific warning on the gas cap saying 91 or higher had to be used. GM ought to know some of the consumers are clueless on what fuel octane is so hopefully they made it fool proof.

The two I had had didn't and the owners manual says it's recommended but if you run 87 oct you will loose performance. It's even worse if you live at higher elevation where regular is 85 octane.

 

[jfoj]

Fuel door has a sticker on the inside that states "Premium Fuel Recommended", it does not indicate the "recommended" octane rating.

L87 spec info from GM Power Solutions indicates Fuel Type Regular Gasoline (87 Octane), with 11.5:1 compression ratio!!

L87 Spec Info

Seems the owners manual for the 2024 indicates that "Premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating (R+M)/2 of 91 or greater is recommended." Not sure what earlier versions listed.

With how the 6.2l is configured to be a Low RPM Torque monster on the highway with 11.5:1 compression, I would never dare to run anything other than 93 Octane.

 

[Scarey]

I don’t think I’ve ever seen 93 at the pump only 91. I’m west coast, is it readily available in other geographic areas?

 

[jfoj]

Yea, the problem with "Premium" fuels is they vary in Octane based on region from what I have seen. West Coast seems that 91 tends to be the typical for Premium. Some higher altitude areas may vary and then Winter blends are also different in colder climates. Winter blends are not supposed to be lower in octane, they tend to be more volitile (lower RVP) to make them easier to "ignite" in colder temps, wonder how this all plays into LSPI in the real world?

 

[KMeloney]

I don’t think I’ve ever seen 93 at the pump only 91. I’m west coast, is it readily available in other geographic areas?

Three's plenty of 93 here on the east coast.

 

[Vladimir2306]

I don’t think I’ve ever seen 93 at the pump only 91. I’m west coast, is it readily available in other geographic areas?

Are there such problems with Premium fuel in the USA? I never would have thought.
In Russia we have 95 grade gasoline, which is 91 in the USA. It’s available everywhere. We have brand 98, it’s about the same as 93-94 in the USA, there’s a lot of it too. And we have grade 100 fuel, which is approximately the same as US standards 95-96. And there is a lot of it, here is a screenshot near my place of work. Of course, we don’t use grade 100 fuel at GM, but I actively use it for my jet ski.

 

[Vladimir2306]

@viven44

Trust me, your 10 speed is getting into 10th gear a lot quicker and easier than you realize. Not in "city" driving will you typically get into 10th gear, but I drive a lot of "rural, suburban" area where the speed limits are 45 MPH on 2 lane roads without much traffic or traffic lights and I will see my Yukon get into 10th gear more often than I would have expected. On the highway or above 50 MPH with a lot of throttle movement, 10th gear is almost always enabled. I watch this all the time when monitoring and pulling data.

I will touch briefly on your fuel economy concern, while the 2018 5.3l 2 WD Suburban indicated it could get 23 MPG on the highway, I really doubt you were much bettering that by 3-4 MPG. I could see it maybe besting this a bit if you could cruise unobstructed at 50-55 MPH for long periods on flat terrain, but besting by 3-4 MPG, doubt it. If you were going strictly but the Fuel Economy read out, this might be part of the issue? This is a whole different conversation I really do not want to get into.

While many of the 6.2l engines are failing before their first oil change, I still believe with many of the bearing related problems it is more oil related than defect related. Sure there can be defects, but the punishment these engines could undergo with 11.5:1 compression ration running Regular fuel and the ridiculous 0W20 engine oil that can easily and quickly loose viscosity when fuel diluted it really not ideal. Assuming people are not running Premium fuel in these 6.2l I really wonder what may be going on.

You should read this post: https://www.tahoeyukonforum.com/thr...-class-action-suit.150688/page-3#post-1951170

It was the same in previous generations. Top gear was engaged at about 50 mph. so it doesn’t matter whether it’s a 10-speed automatic transmission or a 6-speed one, on the highway they drove about the same, 6.2 on the previous generation and 6.2 on the current generation.

 

[blanchard7684]

Are there such problems with Premium fuel in the USA? I never would have thought.
In Russia we have 95 grade gasoline, which is 91 in the USA. It’s available everywhere. We have brand 98, it’s about the same as 93-94 in the USA, there’s a lot of it too. And we have grade 100 fuel, which is approximately the same as US standards 95-96. And there is a lot of it, here is a screenshot near my place of work. Of course, we don’t use grade 100 fuel at GM, but I actively use it for my jet ski.

There are places I travel frequently here that have 86 and 85 octane. These are higher elevation places in southwest.

 

[Vladimir2306]

There are places I travel frequently here that have 86 and 85 octane. These are higher elevation places in southwest.

In principle, our minimum fuel type is 92; according to American standards, this is 87. There is no fuel lower than this octane number at all.

 

[blanchard7684]

In principle, our minimum fuel type is 92; according to American standards, this is 87. There is no fuel lower than this octane number at all.

You mean in Russia?

 

[Vladimir2306]

You mean in Russia?

Yes

 

[Sean Michael]

I really enjoy my 6.2L RST, but after the FPCM left me stranded on the 6th day of ownership at only 320 miles, and now the reports of bearing failures, I'm beginning to lose confidence in the vehicle. I started kicking tires on other vehicles just to see what else I would drive if not a Tahoe. I've owned three Tahoes and love them, but this one is stressing me out. I might return to my sports car roots. I test drove a 2025 Cadillac CT5-V yesterday and it brought back memories of how much I used to enjoy sporty vehicles, I seriously might make the switch. It's world's apart from something like a Tahoe, but my wife said she'd be happy to get a larger SUV for family hauling, maybe a BMW X5, I hear great things about their B58 engine, besides, I bought the 6.2L RST version of Tahoe for speed and fun, it was a compromise between utility and thrill and I don't tow or go off-road or anything that really requires a truck-based SUV, so I might just go all in on a sports sedan that does 0-60 in 4.6 and handles like it's on rails. If I do, I'll miss the 6.2L rumble, especially since I have the GM performance exhaust on mine, but that CT5-V was a blast to drive, and I'm a spirited driver in general. Am I crazy?

 

[LegalBrief]

@Sean Michael hi, I think your over reacting… st 320 miles any “bad part” is shoeing itself, once replaced you should be fine, a vehicle is the sum of its parts.

 

[Sean Michael]

I'm trying not to be neurotic about it, but the fuel pump control module leaving me stranded wasn't a rare fluke, it's a common issue and there's even a thread on this forum about buying and keeping a spare one in the vehicle. I'm not too concerned about the lifter issues everyone talks about, because I've owned three Tahoes with AFM/DFM and never personally had that issue, but the bearing failures have me concerned because not only is it a potentially catastrophic failure to lose power on a busy highway, especially being I frequently have my wife and son in the vehicle, but even if it doesn't create a dangerous situation there's a backlog from all the failures taking months to replace, and some people report the replacement engines doing the same thing a few thousand miles later, and then there's Chevy not being consistent about loaners or reimbursing rentals fully. I really enjoy my 6.2L Tahoe, but every time I drive it, especially with my family, the thought is in the back of my head and it dampens my enjoyment of the vehicle.

 

[blanchard7684]

I'm trying not to be neurotic about it, but the fuel pump control module leaving me stranded wasn't a rare fluke, it's a common issue and there's even a thread on this forum about buying and keeping a spare one in the vehicle. I'm not too concerned about the lifter issues everyone talks about, because I've owned three Tahoes with AFM/DFM and never personally had that issue, but the bearing failures have me concerned because not only is it a potentially catastrophic failure to lose power on a busy highway, especially being I frequently have my wife and son in the vehicle, but even if it doesn't create a dangerous situation there's a backlog from all the failures taking months to replace, and some people report the replacement engines doing the same thing a few thousand miles later, and then there's Chevy not being consistent about loaners or reimbursing rentals fully. I really enjoy my 6.2L Tahoe, but every time I drive it, especially with my family, the thought is in the back of my head and it dampens my enjoyment of the vehicle.

@Sean Michael what year do you have? sorry if you posted this before...

 

[jfoj]

Easy solution for the fuel pump problem. Search my username. I have two spare fuel pump control modules that carry in the truck. And if you haven't locked your engine up yet, change the oil immediately. Don't use 0W-20 oil starting to think 0w40 might be the best option. I just finished a 2-hour run oil temps are up to 226F for quite a while that was only with the 60° F ambient temp. Drive the truck in L9 and/or get a range DFM disabler.

 

[jfoj]

6.2l Range Anxiety

 

[Sean Michael]

@blanchard7684 2024 Tahoe RST 6.2L purchased new last September.​

 

[jfoj]

@Sean Michael

How many miles on the truck? Has the oil been changed yet?

 

[Sean Michael]

@Sean Michael

How many miles on the truck? Has the oil been changed yet?

Approximately 5,000 miles with one oil change at 3,000.