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?