Well, I have almost 30,000 miles on my 2021 Stingray, have done the maintenance pretty much by the book (first filter change was at 6500, and I think before GM came up with the flush procedure and definitely before the requirement to change it again by 8,000 miles) Second filter at about 22,000 miles, with the flush procedure. Fluid was changed just before 3 years. Haven't had a single issue with the DCT. I haven't seen a single bit of evidence that changing filter and fluids twice as often as GM requires benefits anything but the sellers of those products. Unless you're tracking the car - then follow those specific requirements.

 

good info, thanks

 

Sure it does. The manufacturer error was GM made the idiotic recommendation to use 0w-20 motor oil to help with the NHTSA CAFE ratings……a highly ill advised route to eek out a couple of additional decimal points in fuel economy. The crankshaft supplier made in-spec crankshafts assuming GM had used normal 30 or 40 weight motor oil and bearing clearances for a thicker viscosity oil…..but they didn’t. They gambled and lost, and hanging their supplier out on the line as a result……same ol GM as when I worked there 30 years ago.

Hot 20w oil requires a very round and very smooth journal finish on the crankshaft to maintain the proper hydrodynamic oil wedge given the tight journal clearances……a VERY unrealistic expectation given typical mass production variances and volumes. We used custom blended 0w-15 on Cosworth and ILmore IndyCar engines back in the 90’s looking for every HP we could get……but those billet cranks had journals that looked like mirrors.

I’ve had several vehicles that recommended 0w-20 oil, and ignored it without another thought. If L87 owners had done the same and used 30 or 40 weight oils, many of those engines would not have problems.

 

I sent a email to Foxwell to confirm that the NT510 can do the flush procedure for the 2025 corvette. They wrote me back and advised it CAN NOT do the 2025 model year.

Here is their response:
"NT510 elite can NOT do the C8 transmission flush procedure on a 2025 Corvette. The vehicle model is too new, no equipment can be recommended.

If you have any questions, please feel free to contact us."

Has anyone tried the NT510 on a 2025? Not sure why it works on a 2024, but not on a 2025.

 

I agree with your statement - it won't make the defect go away. But it might lengthen the time/mileage until failure beyond the expiration of the Special Coverage which expires in 10 years or 150,000 miles. And I am not suggesting that's a good thing.

The L87 engine issue is little off topic, but came up because it was used as an example of the alleged "fallacy" of following GMs maintenance procedures.According to “Safety Recall N252494001 L87 Engine Loss of Propulsion”, the issue is “The connecting rod and/or crankshaft engine components in these vehicles may have manufacturing defects that can lead to engine damage and engine failure. If the engine fails during vehicle operation, the vehicle will lose propulsion, increasing the risk of a crash.” There is no further clarification of the nature of the “defect(s)” in that bulletin and no indication of which engines in the listed groups have the defect – such as engine numbers, or specific manufacturing dates.

The original announcement

https://static.nhtsa.gov/odi/rcl/202...5V274-6343.pdf

appears to identify engines that already manifest the issue with a very simple inspection – check for DTC P0016. That code indicates a discrepancy between the crankshaft position sensor and the intake camshaft position sensor. One could speculate on the connection between a defect in connecting rod or crankshaft and a resulting discrepancy between the crankshaft and camshaft positions. Regardless, engines (in inventory) that have that code are quarantined pending further instructions. If the engines do not have that code set, then they get new 0W-40 oil, a new oil cap, and new page in the owner’s manual. But, does that mean those engine don’t have the defect, or does it just mean that the issue has not manifested itself? I think the latter, given that they extended coverage for this defect out to 10 years or 150,000 miles.

Some additional instructions “Special Coverage N252494003 L87 Engine Loss of Propulsion were released in May 2025” and apply to customer vehicles that develop an issue.

https://static.nhtsa.gov/odi/tsbs/20...18541-0001.pdf

The Special Coverage for this issue in the additional instructions extends to 10 years and 150,000 miles. To me this implies that engines that do not have this P0016 set and have not developed an issue may develop the issue later on. In other words, absence of P0016 does not establish absence of the defect.

Engines with the code set will be replaced. The instructions include, among other things, the following statement, applicable to customer vehicles brought in with an issue: “If the vehicle is not showing any obvious signs of neglect and has a seized engine or a P0016 code, replace the engine. Refer to Engine Replacement in SI.”

Engines that “pass” the simple inspection for P0016 get sent on their way with new 0W-40. Does this simply mask the defect or prolong the time to failure?

In any case, if the defect is present, no amount of maintenance or switching to the 0W-40 oil is going to remove the defect – but it might lengthen the time until the failure occurs- perhaps after the period of special coverage expires.

 

I did my 2025 Z06 just this past Monday with the Foxwell NT510 elite, no problem.

 

There is no manufacturing defect per se. As gsvette outlined, the recommended oil spec'd by GM was too low thin.

I've said this before - a friend who worked at Ford as a powetrain developmental engineer responsible for engine development told me not to use the 5W-20 oil in my father's 2003 Marauder. He tore down engines after running endurance tests on Ford's dynamometer and they showed excessive wear.

If GM wanted to use 0W-20 in their heavier vehicles which imposes heavy loads on their engines - at low engine speeds, then their machining process would have had to be much finer. And you won't find that kind of prep in a mass production vehicle.

 

excellent, thanks for the input.

 

Occam’s Razor: Between two competing theories, the simplest is probably more accurate.

Theory 1 - A GM supplier using state-of-the-art 5-axis cnc machines manufactures hundreds of thousands of crankshafts with a “defect” that somehow slips by their QC for several years.

Theory 2 - GM’s recommended oil is too thin because bean counters wanted higher CAFE numbers.

Critical thinking would therefore ask, “which of these is more likely”?

For myself, I have an additional data point. I know two farmers that between them have over 10,000 acres, at least a dozen GM trucks and SUV’s with L87 engines in the recall range, and not a single engine problem with any of them including some with high-mileage. Lucky? What’s different about these vehicles? Like most farmers they maintain their own equipment and use bulk lubricants. One of them buy's 55-gallon drums of Shell Rotella T6 5W-40 synthetic oil, and the other buys 55-gallon drums of Farm and Fleet branded 5W-40 synthetic oil, and in either case the bulk lube gets used in EVERYTHING…..tractors, combines, cars/trucks, 4-wheelers, zero-turn mowers, etc. Again, several recall vehicles between them and not a single problem.

It seems reasonable to conclude that GM’s water thin oil recommendation is the likely root-cause of spun bearings and L87 engine failures. That GM then revised the oil spec for these engines to a thicker viscosity after the fact is further confirmation, and typical “lipstick-on-a-pig” GM mentality that I fled many years ago.

Critical thinking is not blind allegiance to so called “Experts” as your previous posts advocate, nor in many cases are these so called “Experts” the engineers referenced below and in others posts. In the same post below, Blindspot literally illustrates his chosen user name by criticizing those who “outthink the factory engineers” (ie questioning their recommendations) and then in the next sentence suggest that those who do so are under the spell of marketing. This is the literal definition of typical group-think and a "blind spot” created by corporate marketing that emphasizes compliance and obedience.

Many times, decisions and recommendations of vehicle engineers are over-rode by various corporate morons who couldn’t find their *** with two hands and a flashlight that are motivated primarily by their own bonuses and stock options. The level at which this occurs would be stunning to most people, and the Boeing 737 debacle is another example that cost the lives of hundreds of people. The advice of these so-called “experts” should always be taken with a grain of salt.

So yes, the GM L87 problems are VERY relevant to the topic of GM lubricant recommendations and service intervals on a unique and bespoke DCT design that is unlike any DCT used in other proven performance cars, has demonstrated recurring problems, and is unable to be serviced except by complete unit replacement. If the TR-9080 was a proven split-sump DCT design that used FFL-4 for clutches and 75w-90 hypoid gear oil for gears, I would be more inclined to follow GM’s fluid/service recommendations, and take problem reports with a grain of salt so-to-speak. But that is not the case, and I know how GM operates internally.

To potentially avoid some of the known issues with the Tremec TR-9080, I will not repeat the same GM fluid and servicing recommendations and expect a different result from those that have had problems, because the definition of insanity is repeating the same behavior and expecting a different result. Based on actual experience and success doing this with my previous 3LT-Z51, and now my ERay, I will continue to exceed GM’s C8 DCT service recommendations by doing a yearly DCT fluid/filter/flush service. I will use a high-quality DCT lubricant from a reputable brand that is not GM/Delco. I will not hesitate to recommend to others to do the same, along with facts and justifications to do so.

Thinking and doing for myself does not make me or my advice to other's dangerous or ill-advised. My ERay being my long term “keeper” C8, I will ignore GM “experts” on this topic, and group-think adherence to their advice.

 

GM is still recommending the use of 0W-20 oil in replacement engines. This can be seen in the bulletins addressing the issue. I’m not disagreeing (or agreeing) with the assertions that 0W-20 or 5W-20 are too thin – just observing, based on the published bulletins, that GM is only switching to 0W-40 oil for those engine that may have the defect, but have not manifested the issue in the form of seized engine, code P0016, or failed diagnostic test (in one of the bulletins).

If there is no defect, it suggests that the bulletins GM has released on this issue, stating that “The connecting rod and/or crankshaft engine components in these vehicles may have manufacturing defects that can lead to engine damage and engine failure” and the report submitted to the NHTSA with details of the defects and how it was addressed for future build are disingenuous. Suggesting GM would rather fabricate an elaborate story about defective engines, issue multiple bulletins with procedures and remedies, submit false reports to the NHTSA, than admit the specified oil is too thin. Perhaps a simpler explanation is to take the bulletins at face value – there is a defect.

There’s even some additional detail available on the exact nature of the defects – there are two - Rod-bearing damage from sediment on connecting rods and crankshaft-oil galleries” and “Out of specification crankshaft dimensions and surface finish”. These flaws were traced to supplier quality issues during the production of the L87 engine. This info is found here

https://lemberglaw.com/gm-v8-engine-recall/

and the official reports on the defect details can be found here:

https://lemberglaw.com/wp-content/up...5V274-1938.pdf

The report says, “A series of crankshaft and connecting rod manufacturing improvements implemented on or before June 1, 2024, addressed contamination and quality issues”.

It appears that GM’s switch to 0W-40 applies only to selected vehicles (certain VIN numbers or engine dates) that did not manifest the defect (P0016 or seized engine) and passed a fairly elaborate inspection. An example of this elaborate inspection appears in the attached bulletin (this one is much, much more than checking for a code).

If it passes it gets the new oil, oil cap, manual page, and the Special Coverage applies (there is a separate bulletin about the special coverage). If it fails, the engine is replaced and it says “transfer the engine oil cap from the original engine to the replacement engine and fill the engine with the oil grade that is indicated on the cap”, which is going to be 0W-20 cap. Again, not defending it, just observing its GM’s instructions.

Another example is this bulletin here:

https://static.nhtsa.gov/odi/rcl/202...5V274-5347.pdf

This one indicates (in case one was wondering about the apparent explosion of bulletins on the subject) that there are 3 bulletins and the applicable bulletin depends on the VIN number. “Remedy solutions for this recall are VIN-specific. VINs are assigned to one of three bulletins. Investigate Vehicle History (IVH) in the GM Global Warranty Management system MUST always be checked to confirm vehicle involvement and MUST be in OPEN status prior to beginning any required inspections and/or repairs.”

This appears to include replacement of certain engines in vehicles that are in inventory (essentially no miles) – apparently because they are known to have the defect. And it says, “Transfer the original 0W-20 Oil Cap to the NEW engine and fill the NEW engine with dexos 0W-20 oil”. It also indicates that if the vehicle has a replacement engine manufactured after a certain date – no action is required (No replacement 0W-40 cap, no change page, no oil change). Once again, not defending any of this – its just what GM has done.

Here is the link to the special coverage announcement, applicable to the set of engines that have or may the defect(s), but were not replaced.
https://static.nhtsa.gov/odi/tsbs/20...18541-0001.pdf

 

Lets just see moving forward how many vehicles still using 0W-20 ever throw a code P0016.

 

I know. Or, one of the other symptoms, which included a seized engine.

The bulletins apply to model years 2021-2024, but GM has been recommending 0W-20 in Chevrolet Suburbans since 2015.

Prior to that the recommendation was to use 5W-30, or for extreme cold 0W-30. And those manual prior to 2015 include this language as well :"Do not use other viscosity grade oils such as SAE 10W-30, 10W-40, or 20W-50." When it was changed to 0W-20 in the 2015 manual, the language about what not to use was dropped.

Again, not defending GMs requirements, and not agreeing or disagreeing that 0W-20 is too thin, just pointing out the situation.

 

No. The manufacturing error was building bad crankshafts that didn't meet spec and then not doing adequate QA on them. Don't know where you come up with the idea that the supplier mad in-spec parts, because they absolutely 100% didn't. GM spec'd parts for the recommended oil, and the manufacturer failed to meet those specs. Suppliers don't get to decide what oil the engine is going to use or what tolerances they build parts to. LOL.

If the parts had been built to spec, the recommended oil would have been fine.

Wrong, wrong, wrong. See above. The cranks weren't built to the required spec. Period.

You've produced not one bit of evidence that the supplier built the parts to GM's spec. All you have is your hatred of 0W--20 oil and speculation. There are literally millions of cars from many manufacturers on the road using 0W-20 oils without any problems at all. Using your logic, we should be running Harley Davidson straight 50W in hot weather for even better protection.

 

How did this DCT thread turn into a motor oil thread?

 

Agreed, anyone else use a Foxwell on their 2025 DCT flush?

 

Agreed, anyone else use a Foxwell NT510 ELITE for the DCT flush?

 

I have not suggested (yet) that GM has fabricated anything regarding the L87 situation, however, the company has a history of lies and deception. I saw it first hand when I worked there in the late 1990’s.

Perhaps you remember “The Cadillac of Lies” news stories in the 1990’s? How about “GM Lied People Died”? or the “pay back in full” BS on the government bailout 15 years ago? Have you ever googled: “GM submits false reports to the NHTSA” as you responded above? If you had you would find from just 7-months ago: "General Motors self-driving car unit, Cruise, admitted on Thursday to submitting a false NHTSA report to influence a federal investigation and will pay a $500,000 criminal fine as part of a deferred prosecution agreement, the Justice Department said. In addition, a $1.5m civil fine has been imposed along with requiring full co-operation with an ongoing SEC investigation"
GM’s Cruise admits submitting false report to robotaxi safety investigation

GM has the #2 largest vehicle recall in history, and that of the top 15 largest vehicle recalls, 5 of them were GM vehicles not including the current L87 situation? 52,000,000 GM vehicles recalled at a cost in the tens of billions of dollars. This is an average of more than a million GM vehicles recalled per year.

GM Lied and People Died

USA Today - GM bans employees from using certain words

My suggestion that the L87 issues are likely an oil viscosity problem is giving GM and it’s suppliers a HUGE benefit of the doubt. These engines have had problems going back to the L86 in 2014 when 0W-20 was first spec’d. GM has manufactured well over 100 million small block engines to date and they are legendary for power and reliability. Suddenly GM has forgotten how to machine crankshafts and 721,000 L87 engines over just four model years have machining defects of such severity that the engine experiences catastrophic failure?…..this would be incompetence and lack of process and quality control at such a staggering level that I find it difficult to believe.

Imho loyalty to “corporate experts” and inanimate consumer products is misguided at best. Loyalty belongs to family, friends, and people you trust….not machines and certainly not GM or any other large corporation that places profits above all else.

 

It was because someone else suggested that "blindly" following GM's required maintenance procedures can lead to issues, and cited the issue with the truck engine defects as an example, because part of GMs response was to switch the recommended oil from 0W-20 to 0W-40. This was supposed to be proof that using the oil recommended by GM leads to engine failures - with the implication that following GMs recommended maintenance for the DCT will also lead to failures. But the switch to the oil was only for a subset of vehicles between 2021 and 2024 with certain VIN numbers that may have the defect but, based on inspection, did not manifest evidence of the issue. 0W-20 has been recommended since 2015 (for Suburbans anyway), and for replacement engines and any engine made after a certain date, the recommendation remains 0W-20.

It may or may not be true that that recommended maintenance for the DCT (or engine oil in the truck engine) is not adequate - but a better way to prove that would be with actual analysis of fluid drained following the procedures compared with more frequent fluid or filter changes. Or, some correlation between failure rates and alternate maintenance procedures. Or an engine or transmission teardown and inspection for wear - though a single instance of that is merely anecdotal.

 

It’s not a motor oil thread. The L87 problems, and GM’s CYA pivot to thicker oil brings into question the validity of their recommendations…..and this is absolutely relevant to GM's C8 DCT servicing and lubricant guidelines that many here follow without question in spite of continued reported problems. I would like to avoid these problems, thus I provided details as to why and how.

Following the GM owners manual and running the DCT filter for 22k miles, and the Delco oil for 3 years/45K miles on the only shared sump wet-clutch DCT?…..well that's your choice……but it will not be mine.

 

….and that’s exactly what I (and several others) have done with my previous C8, and will continue to do on my ERay.

I’ve posted several threads on DCT servicing using Valvoline fluid, economical scan tools that do the flush/leak test, other related tools, and how reasonable it is to take 2-3 hours of time and $175 total cost to do it yourself yearly, avoid metallic/clutch buildup in the DCT that has proven to cause problems, and avoid the hassles of “dealer service"