Hi C8 Friends,

Posting on behalf of one of our club members, so please bear with me...

Just bought a 2023 C8 with 5,500 with no record of transmission service, and when we called the local dealer today, the freebie expired this past March. Was quoted $1,300 for a full trans fluid/filter service.

Should we do the service now or wait for 7,500 miles?

 

The filter must be changed between 7000-8000 mile regardless if you do it early. The fluid needs to be change at least every three years regardless of mileage (or when the fluid life monitor says, or 45000 miles or every 24 hours of track use whichever is first). At this point, you do not need to do anything yet - unless you wish to do it more often than the manual says. But no matter how often you change the filter before 7000 miles, it still needs to be changed in that 7000-8000 mile window to comply with the requirements in the manual.

 

Do the DCT external filter change between 7000-8000 miles. No less, no more to keep warranty intact. If that mileage happens next year, do the filter and fluid change. The owners manual has the details on mileage and times for service.

 

Does the $1300 include ALL the fluid or just the replacement/top off when they replace the DCT filter?

 

Depending on the date of manufacture, his 3-year DCT fluid change may occur in 2025, not next year. I have a MY2023 that was built in October of 2022, so my 3-year fluid change is coming up THIS year (2025).

 

I could be mistaken but I believe the clock starts when you take delivery. In my case it was only a couple of weeks difference. I can’t imagine an issue with GM saying it starts when the car was finished. When was the DCT filled? I suspect a good amount of weeks before GM put it in a car. But your point is well taken.

 

Well, the wording the Warranty Manual makes it look like, for all the world, that the warranty clock starts when the car was delivered. But I can tell you that in my case,the warranty clock started a week or so before that when it rolled off the line and was invoiced to the dealer. I can tell this from the date recorded in my on line chevy account. Yes, maybe if I had an issue in that short period it would get it covered. Does the fluid life clock start when the warranty clock starts? I don't know - but am sure there are lots of opinions. I just made sure my fluid was changed three years or less from the warranty start date to avoid having to deal with even the possibility of an issue. Its only a matter of a week or so.

There is some evidence (strong evidence actually) that the engine oil life system "clock" will not start in this bulletin that describes, at a high level, the factors considered in the engine oil life calculation:
https://static.nhtsa.gov/odi/tsbs/20...02441-0001.pdf
which says
"The OLM starts its calculation for all pathways after the first 50 miles (80 km) to account
for marshalling and time before sale. Subsequently, calculations begin immediately after
each reset."

In other words, it would appear that GMs intent is not to start the clock until after the sale for engine oil life.

The transmission fluid life system does not even account for time or the three year requirement, so the owner has to observe that.

 

And what about a new C8 that has sat on a dealer lot unsold for 12 months? Would the DCT fluid need replacement two years after that?

 

That would be a big ask for anyone buying the car. What if was 2 years on the lot? Is the DCT really going to have a problem with "unused" DCT fluid in the case for an "extra year"? I'll bet not and the risk would be extremely low. If the DCT is that sensitive to unused fluid breakdown for a year there are bigger issues with the trans design.

 

According to Josh Holder when asked about the reason for the three year change, its not just "breakdown" of the additive package it moisture absorption:

".... "The fluid needs to be changed after 3 years because the anti-foaming agents will break down and the fluid will absorb some moisture. All service recommendations are for good reason ."

Right or wrong, and I'm not going to debate that, the statement is from a GM rep and might represent GMs position on it - meaning they might assert that it needs to be changed.

To be clear, I am not saying it would or would not be harmful to the transmission, whether or not the transmission is sensitive, or whether the risk to the transmission is extremely low or not. In my opinion, that's not the point. The point is whether or not GM would deny a claim if have a transmission issue and the fluid was not changed for longer than three years from the day it rolled off the assembly line (or even if you took delivery and stored it for three years without driving it).

I think if I were buying a car that sat on the dealer lot for two years, I would want to have the engine oil and the fluid changed out - and I would have a lot more questions about why it was there for two years, and where it sat. Cars that sit a long time tend to collect critters etc. - so the question is bit hypothetical anyway.

 

OP FWIW
$1300 is average for the cost, and would include a new filter.
(Perhaps $400 of that cost is the under panel Remove and Replace LOL)
The filter is about $200.
If you don't have the required 7500 miles, at a minimum at would change the trans oil at the 3 year mark.
Then again at 7500.
I would do the filter and oil now, and then again.

 

The fluid is hygroscopic?

 

Assuming that means that will absorb moisture, here is what Josh Holder said when asked about why it must be changed at least every three years:

.... "The fluid needs to be changed after 3 years because the anti-foaming agents will break down and the fluid will absorb some moisture. All service recommendations are for good reason ."

Here is a link to discussion that claims transmission fluid is hygroscopic:

https://wheelsbyjason.com/is-automat...d-hygroscopic/

 

When I took my (new to me) '23 to the dealership for the recall of the OBD interface system, the tech printed out a sheet of mandatory service intervals.
He made sure I saw the DCT service, and said that it was NOT a DIY item. Corvette Connection in Denver said the same. It MUST be performed on time,
and at a Dealership to be logged into the vehicle service record, or you're on your own for any future problems.

 

That requirement would be a violation of the Magnuson-Moss act unless they do it for free.

 

Sounds like the dealer trying to put the fear of non warrantied repair into you!

 

- the owner's manual is clear a that you can perform your own service if you document it, and Josh Holder said that the DCT filter can be done DIY without the dealer performing the Hydraulic Flush Procedure. The dealer is just trying to do what many of them are good at - take advantage of owner's ignorance.

 

Agree, both the Owner's Manual and Warranty Manual make it clear that one can perform their own maintenance. Agree that Josh said that a DIYer can skip the HSF. That said, I do have mine done by the dealer, and I do expect the dealer to perform the Hydraulic System Flush per the DCT external canister filter change procedure. DIYers that wish to do the HSF (and many do per all the threads about scan tools that can support the HSF) will need to obtain a scan tool with that capability.

Josh's description (included below) of the HSF differs a bit from the Service Manual description (attached). Josh made it sound like all it does is "force more fluid through the filter". He did not mention the actuation of the solenoids in a specific manner to flush debris from the system. Note that he says that during normal highway driving a routine runs to force more fluid through the filter, but he does not say it is the Hydraulic System Flush routine (and earlier models did not even have the built in software to do the HSF). I do not believe that same HSF process can happen during normal or highway driving.

"Josh Hoder: The hydraulic system flush does kind’a the way its described. It forces transmission fluid through the fine filter that you replace. So, at a dealership they can hook up the dealer service tool to the and run a routine that will tell the trans control module to do this fluid filter flush. And because the car is already hoisted on the rack, the technician’s already got the panels off, there’s some other work he’s doing, this kinda happens in parallel in the background. So we’re doing it at a dealer visit because we can. And we can take the last bit whatever contamination might be in the oil and get it into the filter before the technician replaces it. Do it yourselfers have become nervous that hey now I can’t do it myself, I don’t have a service tool, I can’t force this routine. You don’t have to do the routine. Like I said we do it because we can, but the fine filtering routine happens during normal driving anyway. In fact, when you’re driving steady state like say down the highway, we run a routine in the transmission that will force more of that fluid through the fine filter. So normal driving is doing this. If you are a do-it-yourselfer, you don’t want anyone else touching your car, you can change the trans filter without running this routine."

 

Clock starts on Build Date. I have a 2023 HTC and received a notice on Trans Fluid change to be done by 9/10/2025 car built 9/10/2022 also just purchased 3 yr 60k miles GM Warranty starts 9/10/2025

 

Where did the notice come from? I never received one. While I would assume that it does start on the build date, just to be conservative, I have never seen anything that says exactly when the clock starts. My warranty start date appears to have been when the car was invoiced to the dealer - neither the build date nor the delivery date (not that it proves anything about the start date for the transmission - it just illustrates inconsistency). Others have seen different start dates for their warranty.

Also, according to a GM bulletin about the oil life system (not the transmission fluid), the oil life system has a built in 50 mile delay before the countdown starts. So, at least for oil life it would seem that the clock starts after 50 miles which will typically be after delivery, rather than build date.

I found no similar documentation about the clock start for the transmission fluid replacement.