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

[viven44]

@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.

Finally got to this after 3 months. Lo and behold my scanner did the software update for GM in 2 mins, ha ha

I was watching it get up to 8th gear as low as 38mph in city driving, but dropped down to 4 when the throttle was pressed any.

See below graph on how it shifts on the highway.

On the highway, merging to about 60mph was in 6th gear and I drove it really gently at ~55-60mph to see if it would get up to 10th gear, it actually did to my surprise. it slowly got up to 10th gear and stayed there but the slightest bump in the throttle got it down to 8/9.

I didn't get the chance to drive over 70mph, but I'm fairly confident we don't see it holding 10 long if/when that happens

 

[jfoj]

6.2l Recall With Lake Speed Jr and other YouTube Automotive folks

GM 6.2l Recall

 

[Polo08816]

https://gmauthority.com/blog/2025/05/6-2l-v8-l87-recall-heres-how-many-engines-gm-expects-to-replace/

"Affected vehicles may be equipped with a defective engine that could fail, leading to a loss of propulsion and posing a potential safety hazard. According to recall documents, GM estimates that roughly three percent of the L87 engines impacted by this recall will need to be replaced."

At least 3% is a pretty high failure rate.

 

[jfoj]

YouTube Video With Some GM Inside Info

 

[viven44]

Looks like the Corvette cranks are made in the NY plant and it sounds like the truck/SUV crank production was moved Mid-2024 to the NY plant.

 

[jfoj]

I was aware of the 6.2l cranks being made in Mexico and assumed GM moved production back to the US.

Not sure the video has a lot of solid smoking gun stuff at the moment, but usually inside sources need to feel out the presenter to make sure they are comfortable what info they provide. Hopefully there may be some follow up with more meat and potatoes.

 

[viven44]

Yep, just relaying my "glass half full" view of that video. "glass half empty" view is that the video didn't tell us too much than we already knew or could have guessed, except to expect more in the future.. good to have an insider

 

[jfoj]

Need to vet your source(s) and the source(s) need to have confidence in the presenter. Tip toe around a bit until both parties are comfortable. Hopefully there will be more to come.

 

[jfoj]

Interesting links regarding final crankshaft polishing requirements and procedures. The thinner or lower the viscosity the oil, the smoother the crankshaft bearing journal finish needs to be. Additionally heavily loaded engines also need an extremely smooth final crankshaft finish. Most articles reference Diesel engines as heavily loaded engines, but the way the 6.2l engine is loaded at highway speeds, it effectively sees loading similar to a Diesel engine. Rougher crankshaft final polishing does not do well with lower viscosity oils. Additionally the wider the bearing clearances the higher the oil viscosity needs to be.

Based on the 6.2l Recall info and other info available, it appears that the main culprit of the 6.2l engine bearing failures had to do with final crankshaft finishing being too coarse and therefore causing problems with the 0W20 engine oil. It seems the majority of the 6.2l engine failures were under high loading conditions, Low RPM/High Torque situations at highway speeds for longer periods.

The crankshaft surface finish being too coarse along with possible increased bearing oil clearances is why GM is changing to 0W40 engine oil for Recalled engines that "Pass" the noise and knock test using the knock sensor mounted to the engine block for the Pass/Fail inspection test.

Is the change to 0W40 engine oil on the 6.2l engines that pass inspection good enough to keep these engines alive for many miles? It seems to fall in line with what a rougher surface finish on a crankshaft would require, but has some damage already been done on these engines? I guess only time and mileage will tell, hopefully the GM Pass/Fail test and the 0W40 oil viscosity change will keep the 6.2l's that "Pass" the noise and knock test alive for many miles to come.

Mahle Crank Polishing

Grish Crank Polishing

Grish Why Crankshafts Need Polishing

Crankshaft Journal Finish

Modatek

 

[RG23RST]

Finally got to this after 3 months. Lo and behold my scanner did the software update for GM in 2 mins, ha ha

I was watching it get up to 8th gear as low as 38mph in city driving, but dropped down to 4 when the throttle was pressed any.

See below graph on how it shifts on the highway.

On the highway, merging to about 60mph was in 6th gear and I drove it really gently at ~55-60mph to see if it would get up to 10th gear, it actually did to my surprise. it slowly got up to 10th gear and stayed there but the slightest bump in the throttle got it down to 8/9.

I didn't get the chance to drive over 70mph, but I'm fairly confident we don't see it holding 10 long if/when that happens

View attachment 457062

SPS says strategy code for 5.3/6.2 TCM is the same so there won't be any difference in shifting. 10th is your prime highway gear and either configuration will stay there at steady speed up to 80mph or higher when not trailering. Lugging the engine is bad for emissions so that's why you see any modern automatic downshift if you breathe on it at all.

It's quite funny to see some members on here talk about the 5.3 like it's a 2.5L 4-banger. Torque demand is torque demand and the 5.3/6.2 aren't much different at all in VE mapping. Sure the 6.2 has more headroom but on the highway both are wheezing through a mostly closed throttle valve.

Know what engine also has no trouble maintaining 10th gear from 58mph up to 80+? The mighty 3.3L V6 with 265lb ft of torque used in newer F150s that got paired with the 10R80.