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

[jfoj]

The one obvious difference between the 5.3l and 6.2l is they all have the same basic variable displacement oil pump, ALL but the newer L84 5.3l have a 2 stage oil pump that is controlled by a solenoid that is not serviceable, this is why there are different oil pump part numbers for the L84 5.3l, vs the L83 5.3l and the L86/L87 6.2l.

Please understand the variable displacement oil pump is the BASE for the 2 stage oil pump. The only difference on the 2 stage oil pump is the solenoid that boosts the oil pressure somehow. I beleive the default/failed/unplugged state of the 2 stage oil pump is high pressure.

I do not think there is enough known about the AFM/DFM behavior if the oil pressure is constanstly boosted. There would likely be a CEL/MIL/SES triggered as well.

Agree that there may be an oil starvation issue when all the DFM activity is happening.

#1 rod bearing is the absolute last bearing in the lubrication path, just behind the front crank bearing. Seeing probably more of these failures out of most bottem end failures, but there are also problems with the thrust bearing on the center main, have alse seen rod bearings #7 &#8 fail as well. Probably a number of different things going on here.

 

[viven44]

Unfortunately the 6.2l is a perfect storm for self destruction. Since the 10 speeds have showed up the problem has been even more prevalent due to the Low RPM/High Torque loading on the 6.2l.

10L80's final drive ratio (0.636) is honestly only slightly lower than even the 4L80s (0.696) and on our 2024, we are honestly never in the final drive gear ever. It takes too darn long to get there, so I've complained about poor fuel economy partly because of that. Can read here.

At a high level I share your sentiment on the poor engineering decisions by ALL manufacturers, not only GM, in the name of innovation. I work in a tech company and sadly when innovation is forced without a need, poor ideas do end up getting implemented often.

Very disappointing to see the 6.2L engine failures being reported everywhere (here, reddit) and we dodged a bullet buying wife's 2024 with the 5.3L. We strongly considered the 6.2L until we realized it needed premium fuel (yes that was the deciding factor!) ... I'm very skeptical even with the 5.3L DFM engine because I'm an old school carburetor/flat tappet guy and like to get into and out of my engine without the need for computers and technology and expensive replacement parts. Set of flat tappet cam and lifters is still affordable (But even that is under peril, more below).

Would be interesting to see what comes out of all this investigation. Premature to say what went wrong. Poor build, poor metallurgy ? Whatever it is, it is not a 6-sigma production. There is an eerie similarity to the flat tappet lifter/cam plague where the lifter and cam lobes flake off due to poor case hardening. Less prevalent but even the Ford 7.3L godzilla has some reportings of low-mileage roller cam/lifter failure due to flaking off.

All the suggestions on oil type, fuel dilution, oil temp can help ALL, but not the few that are sadly driving production outliers with the engines failing within 3000 miles???.. its a spectrum so the not so bad ones are still ticking timebombs... hopefully GM will do right by all and save themselves and everyone involved by getting to the root cause.

 

[jfoj]

@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

 

[viven44]

Trust me, your 10 speed is getting into 10th gear a lot quicker and easier than you realize.

No it isn’t. I’ve been driving automatic transmissions, all the way from 3 speeds to 10 speeds and I can tell what gear it is in based on RPMs. I’ve adjusted shift characteristics on old school vacuum modulators, TV cables you name it. Unfortunately newer transmissions are all computer controlled and only dialed in by software.

Our suburbans shift schedule is definitely geared NOT for mpg. We are not in final gear very long. Usually in 8 or 9.

If your 10 speed experience is solely based on your 24 year model vehicle, you should definitely take it to the dealer maybe consider getting the transmission shifting characteristics evaluated and adjusted if it’s not normal. It is definitely a bad idea to be lugging any engine for that matter.

Our vehicle doesn’t shift like yours and that much I can confirm confidently. I don’t know if GM has setup the 10 speed to lug more on the 6.2L because it is more capable or maybe they are trying to meet EPA rules for 1/2 ton trucks but your shifting into final drive definitely is different than ours.

 

[iboughtatahoe23]

What about AFM?! is this not related

 

[jfoj]

@viven44

You cannot easily tell if the transmission is shifting between 9th and 10th gear and vs versa. Between the TCC slip design and the very small gear ratio difference between 9th and 10th gear, you may not notice it much. The transmission progamming differences between the 5.3l and 6.2l are different, I have confirmed this. But if you are really located in Dallas the road a fairly flat and the 5.3l should be able to hold 10th for a bit before it may downshift into 9th gear. I can monitor and log what gear my transmission is in and I was watching it the other day in a rural setting where I would hit 10th gear at 45-50 MPH, usually below 45 MPH it would usually not shift out of 9h gear.

There is nothing wrong with the my truck as configured, this is the way GM has set them up. At 55 MPH my engine is turning 1200 RPM, at 65 MPH my engine is turning 1400 RPM. The 6.2l is behaving like a Diesel the way it is programmed. Now you might understand why so many of the 6.2l are suffering from bearing failures. The 6.2l has more lower end torque than the 5.3l, but the 5.3l will shift into 10th gear probably around 50 MPH, it just may shift out of 10th or even 9th gear earlier than the 6.2l.

 

[jfoj]

@iboughtatahoe23

I do believe AFM/DFM does not help matters with the 6.2l when running at such Low RPM/High Torque loading. But just think about the 0W20 oil even when fresh and new is probalby borderline for this level of Low RPM/High Torque loading.

Thin the oil out with fuel, run the engine a few quarts low on oil. As the engine gets low on oil and if you continure to operate the engine in situations where fuel dilution will occur, your fuel percentages just keep going up until you add fresh oil which will reduce the fuel percentage for a while, well you might see the writing on the wall.

Will be interesting to see if the 6.2l failures slow down as the weather warms up as well.

 

[viven44]

I can monitor and log what gear my transmission is in and I was watching it the other day in a rural setting where I would hit 10th gear at 45-50 MPH, usually below 45 MPH it would usually not shift out of 9h gear.

I can as well with my high level bidirectional scanner. If you’d like I can monitor gear vs speed and chart it. I’m fairly confident we are not getting past 8 until we are over 60. Ours doesn’t get into 10 unless the torque demand is really low and speed is over 65mph.

 

[jfoj]

@viven44,

The TCM is all about Torque Managment these days. The 5.3l is a different beast that has less Torque than the 6.2l and will have differnet Torque Management mapping for the transmission. I would like to have data to compare the 5.3l operation and Torque loading. I think the 5.3l relies more on RPM's than brute Torque and this may be why the 5.3l are living longer.

I think based on your comments about my truck needing to go to the dealer for transmission mapping changes, tells me you are just starting to understand why all the 6.2l engines are dropping like flies. It has to do with the fact they are configured to run at Low RPM/High Torque and they have absolutely no safety margin when it comes to oil and LSPI and if you are not running Premium fuel, god help you!!

 

[viven44]

and if you are not running Premium fuel, god help you!!

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 w/manual trans 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.