Andybump

Jerry, the context of his question was the case where the overfill did cause an issue. The clue to the context was the reference to causing limp mode. In the case cited, there was apparently no damage, and no visible CEL on the dash, but a sensor was impinged with spray, falsely causing an overheat condition and a slow down (I do not know if that was technically limp mode, as the car could still go pretty fast). That might mean there was an internal DTC set (although a code was never mentioned); Not all DTCs result in a CEL on the dash. His question is did an overfill condition ever result in CEL on the dash. Given the context (that an overfill did cause an issue) its a reasonable question. It there was no DTC, then its interesting that the car will sense an overheat condition (albeit false) and then "limit torque" anyway.

Here is the case which prompted his question:

"A Solution To A Long Term High Speed Problem From Corvette's Chief EngineerI drive my 2022 C8 Z51very fast in the open road races several times a year. This is the fourth Corvette I have used in these races. The C8 is by far the best above 150 mph. But my car has a problem that has shown up three times and cost me finishing well. No DTC codes ever show up. All the fluid and air temperatures are well within limits.

After 30+ miles of 150 mph driving on a warm day, the car slows down. Foot to the floor is 155, then 150, then 145. For the next 30 miles the maximum speed wanders around between 135 and 145 mph. No gear changing or mode changing makes any difference. It just won’t go fast. My dealer and service advisor are very good but they can’t find anything. This is a CND -Can Not Duplicate.



With Jeremy Welborn’s help (thank you very much), I managed to contact Corvette’s Chief Engineer, Josh Holder and Lane Rezek, Corvette Brand Quality Manager. Through several email conversations we tried to isolate the problem and eliminate false paths. I sent them PDR files and other diagnostic files from the road rallies. I use Cosworth’s PI Toolbox and already knew there was nothing in the normal OBD II at the ALDL that would help this problem. Josh and his staff concluded the same thing.

Before my last high-speed event in October, Josh had a field engineer meet me at the dealership. I left the car with Lee Williams for several hours. He installed a custom-made data recorder on the ALDL (OBD socket) and mounted it securely behind my seat. I had a button mounted by my right knee to push when the car started acting up.

Event day was cool and I was afraid that nothing would happen. I drive this car as fast as I can until I reach a finish solution, then I slow down as required. Well, the car decided to slow down first. I was in the middle of nowhere with no cell service or anything else. I had no idea if the recorder captured the slow down event data and whether it was able to upload it.

A few days later Josh emailed that the needed data had been received and his engineers were working on a solution. Today I got an email with the summary of his investigation and a simple solution. All this preamble to the solution is needed. There are going to be some people very surprised by his answer. But remember where this came from and his position. Here is his answer.

On October 27, 2023 Josh Holder wrote:

When you can schedule a visit to your dealer to return the data logger, please ask them to REMOVE 2L of oil from your transmission. The +2L fill was intended for “track” use as in “closed road course tracks” with sustained high G loading. You aren’t doing that in this event. Frankly most people would never see pressure drop outs even on a road course track at the factory fill level.

When the transmission has the extra 2L of oil, the sump level allows 6th gear (which you are in a lot) to spray oil directly onto a temperature sensor. When subjected to high load, like wide open throttle for long durations, the oil spray from 6th gear gets hot enough to cause the sensor to report to the transmission control module that it should begin to limit torque to protect itself. That is exactly what is happening to you. It’s a localized spray of hot oil. The sump average temperature is still quite low.

For the Z06 and all Corvettes built after July of 2023. The case and lube system have been revised so that the extra 2L of oil is no longer required for any situation.

That you very much for your willingness to help us out. We could not recreate the problem in our own vehicles because they were not track prepped for high-speed run (It does not meet our definition of track use), but I can completely understand why it would seem logical to add the 2L for your event. It just was not intended for that use case.

Drain 2L and you should be good to go."

Red Mist Rulz

I think most dealers have a set charge for each of those services, and are going to charge you the full price even if they do them together. Maximizing profit is the name of the game.

Red Mist Rulz

Yes, the change transmission fluid message is mileage based only. It won't come on until 45,000 miles, even it if takes you ten years to get there. And at 45000 miles the DCT filter also needs to be changed. The filter does NOT need to be changed at 3 years, unless you're also hitting 7500, 22,500, or 45,000 miles.

Andybump

Agree. I thought I was making that point when I said those were mileage based, and there is no equivalent statement to change the filter if the fluid is being changed because of the three year requirement.

at7000ft

Thanks for mentioning the Costco discount thing, didn't know it was available.

Avanti

Welcome to the lofty world of Corvettes. Pay-up... or, find a competent and knowledgeable private shop or learn how to do it yourself. All the best, in any event.

JerryU

I answered your question where you quoted my statement:
"Has anyone reported a CEL due to overfilling you related to my statement"?

I was indicating IF you did not add the 2 quarts OVERFILL and were going down the steep turn (like the Laguna Seca Corkscrew) at a high lateral "g" then it might trip a CEL because one of the pressure sensors would detect fluid leaving the pick-up at the bottom of the case.

So your question "has anyone reported a CEL from overfilling" would not happen. The issue with OVERFILL if you are not Tracking is the extra Drag (causing a slight decrease in mpg, quoted by Tadge) and possible foam that can occur with higher fill than needed in gears. Neither would cause a CEL! Foam causes inferior lubrication that could be a longevity issue BUT would not cause a CEL.

Lots of info on the lubricating issues with oil foam. In fact, my early 2014 C7 Z51 (got September 2013) did not warn of possible oil foam until a bulletin November 2014. That said GM would pay for an oil change at 500 miles in dry sum engines only because "Curing engine seals might cause silicone entering the oil to deplete the antifoam additives in the BG installed oil." All lubricating fluids have antifoam additives and silicone is a known product that causes depletion.

I avoided pics but Banks clearly shows the issue with foam in a dif.

EvanD

Damn, really? I guess I can be happy you waited a couple hours with your rambling, repeated, non answer.

Red Mist Rulz

If foaming were an issue with the 2 quart overfill, I don't think GM would say it's OK to leave it in the transaxle for street use. There's no reason to assume what happens in a traditional dif with too much gear oil is going on inside the DCT with a completely different construction and fluid. And the C7 dry sump foaming issue is even less relevant, as it had nothing to do with fill level, and the DCT doesn't use silicone adhesive on its seals. Might as well say that putting too much lubricant in a GE9X Turbofan airplane engine is relevant to the C8 DCT.

JerryU

Just got home was having my E-Ray treated for some PPF by the Shop Owner with about 5 of his ~10 employees helping! Making a Doc as a PDF to post.

Appears you need a max 280-character answer and don't want to digest the technology.

Here is the answer: Never said adding 2 quarts OVERFILL would trip a CEL. Never would as I understand the technology.

SIDEBAR
Sorry I often post answers for others (particularly for the large Silent Majority) some want to understand the technology. In this case about <25 of the Vocal Minority Posted on this Thread versus ~1000 Silent Majority who visited but won't/don't post. At Cars & Coffee asked the ~40 Vette Owner's (out of ~400 cars last month) if they use the Forum. Some said they look BUT won't post as to many negative comments they won't tolerate. Lucky I'm not one! Get PM's thanking me for my posts!

JerryU

In My Opinion: GM and Tremec probably considered the issue. If they thought a possible problem (may not be, tests would show) the tradeoff was no doubt felt worth it by GM for the 5% of folks who Track. Could be the reason Tremec, who designs and sell thousands of transmissions, did not put an extra check level/fill plug higher so you did not have to take the car apart to add AND so you can check the level. Which after you add the 2 quarts OVERFILL you can't (I use the word because that is what Aaron Link GM Exec used when he said NOT needed in the 2024 case.) Tremec did redesign the DCT case around end year 1 to eliminate the area where casting porosity was the cause for weeping fluid. Would have been a perfect time to add the higher EXTRA fill plug. Versus what GM found at the last minute when Track Testing and the OVERFILL 2 quarts was their quick Band-Aid solution. If as Tadge said only 5% of Vette Owner's Track not statistically an issue IF it is a possible problem (may not be.) I pleased Tremec waited and solved the issue the right way for my E-Ray case!

I'll put in a Pic just to show what fluid level is needed for gears. I have not said FOAM IS an issue just that it might be. I'll leave the answer as Don't Add If Not Tracking to the GM Tech's video where he says that several times.


Folks can and will do what they wish, their car. BUT don't add thinking if some is good, more must be better!
It's a Forum and hope folks don't want us all to agree! I spent a lot of time investigating oil foam when 13 months AFTER I got my 2014 C7 Z51 GM issued a bulletin that said because of possible oil foam they were giving a free oil change after 500 miles on dry sump engines. Was well past that mileage by then! Oil foam has nothing to do with silicone depletion of antifoam additives except in the GM and similar instances instance. It occurs pumping lubricating due to many factors. Aerating was the cause in the Banks case I referenced.
I do drive aggressively occasionally hitting a high lateral "g." But we're flat as a pancake in NE SC. So my 1.3 peak "g" turn was not a concern to me and no CEL with the standard fill. My choice after reviewing available data not to add,

cabanamac

Still expensive at $800, but Henna Chevy in Austin wants almost $1200. Few good videos on Youtube of completing if you want to do on your own and don't require pulling the trunk liner.

JerryU

IF you are adding the OVERFILL 2 quarts you add whatever amount (including the ~10 quarts when replacing all fluid (minimum every 3 years) in the check level/fill plug. No need to add any other way.

Red Mist Rulz

You're still trying to conflate gear oil in a differential with FFL-4 ATF fluid in a DCT. And with the C7 oil tank sealant issue with a car that has no plastic oil tank or silicone based sealant for the DCT nor remotely the same oil. Totally different technologies in both the unit and the oil. Unless you can come up with ANY evidence of foaming in the DCT, why don't you give it a rest.

JerryU

^^^
Never said silicone has anything to do with the DCT possible oil foaming! The silicone was an issue with the C7. That GM Bulletin saying change at 500 miles to avoid possible oil foaming came out 13 months AFTER I got my 2014 C7 Z51. It caused me to investigate oil foam at the time. There is an extensive technical info on oil foaming and it's negative effects on lubrication! Very little related to silicone depleting antifoam additives. There are many reasons for oil foam, one is in pumps, another is gears spinning at high rpm.

As Banks showed, the oil foam they encountered had nothing to do with silicone. All I have said is it might be a problem. The additional drag and the possibility of oil foam is what I have said, not that it did occur. I also said GM and Tremec probably looked at the tradeoffs and with test data felt the OVERFILL was worth it.

Could that be a reason Tremec, who has a financial responsibility for failures for a period of the warranty (typical automotive supplier contract) not want to put another check fluid level/fill plug above the existing one?? That would have been easy when they made the case casting changes end 2020 to eliminate the high fluid seepage area caused by porosity in aluminum casting.

I'm glad they fixed the issue the right way for my E-Ray rather than the GM Band-Aid. I don't Track and therefore didn't OVERFILL. No need and there are known downsides and possibly others!

The GM Tech who took ~50 DCT apart and in his video showed the DCT is well protected with >100 CEL possibilities. It has sensors that would catch low pressure etc. He stated several times if not Tracking, Don't add! extra fluid