Does the 2025 C8 trans need to be serviced after three years or this a thing of the past, I’m confused. Thank you

 

Per 2025 owners manual l "The transmission fluid must be changed at least every three years and the Fluid Life System must be reset."
See pages 331 & 332 in this manual it should address your confusion.
2025CorvetteOwnersManual.pdf

 

Don't forget the DCT filter at 7500 too.

 

Should you change your oil annually? I bought a new HTC in August of 2023 and had the oil changed in August of 2024. If I don't have 7500 miles by August of 2025, should I still get the oil changed or can I wait until I get to 7500 to get the oil, DCT filter and transmission fluid changed?

 

You have a two year clock to get your free oil and DCT filter service. It would be wise to get to at least 7000 miles before the clock runs out and do everything at that point. It will be expensive if you don't.

 

The engine oil and filter, DCT filter and DCT fluid are all on different cycles. Refer to your owners manual for each one and remember some are by time, some by miles and some by both, whichever occurs first.

This has nothing to do with the timing of free services, which are on their own time period.

But an easy answer to your, I assume you are talking engine, oil annually. Yes it is required at least annually. Your engine oil monitor will take into account miles and time so go by what it says.

Your car is just over a year old and Aug '25 will be two years old so not due for the DCT fluid change.
You don't have 7000-8000 miles on your car now but when you get in that window you need to change the DCT filter. If it coincides with the free get it done, the DCT filter costs more than a single oil change. If both can be done just before Aug '25 do them together. The DCT won't be due and they won't change it for free.

 

Yep a real shame that GM dropped the Maintenance Table from the Owner's Manual! My E-Ray is the 1st Vette of my 7 that you had to hunt for what Maintenace is required. My 2020 (and thru 2022 as I recall) Owner's Manual had it. First page I went to when I looked at the Owner's Manual. That Table and the page with footnotes made it clear what was needed when, beit miles or time. From my observation those who look at anything will probably see it! Foolish to drop.

Here is the DCT maintenance requirement from the 2025 Owner's Manual:
The initial transmission external canister filter change must be performed at 12 000  km (7,500 mi). If the canister filter is replaced more than 800 km (500 mi) prior to the initial 12 000 km (7,500 mi) break in period, the filter still needs to be replaced again within 800 km (500 mi) +/- the 12 000 km (7,500  mi) service interval..... Check the transmission fluid life percentage. If the percentage is less than 10%, replace the fluid and external canister filter. ... Or when the CHANGE TRANSMISSION FLUID SOON message displays, change the fluid and external canister filter within the next 1 000 km (620 mi). ...The transmission fluid must be changed at least every three years and the Fluid Life System must be reset.

Yep buried in the long paragraph is the key for many Vette Owners who don't put on a lot of miles/year--the DCT Filter must be changed at 7500 miles +/- 500 miles (even if you changed it at 6900 miles!)

Engine Oil/Filter Charge is foolishly confounded with mileage requirements. Was not in my C6, two C7s which simply said as it does here with many foolish words, change when the OLM says!
It only says to CHECK the ENGINE OIL LIFE Percentage (at 7500 miles.) Make's folks you think Mileages as it was in the 1988 and 1993 Vettes before the Oil Life Monitor. BUT my 1993 Vette Owner's Manual stated if most drives are less than 4 miles or mostly stop and go riving change oil at 3000 miles OR 3 MONTHS WHICHEVER OCCURES 1ST. That is because miles is a poor indicator of when to change! Are they GOOD Highway miles OR POOR City miles, lost of start stops, many cold starts. NOTE the ONLY thing that defined when to actually change oil in the OLM! Period.

Every 12 000 km (7,500 mi) • Check engine oil level and oil life percentage. If needed, change engine oil and filter, and reset oil life system. Or when the CHANGE ENGINE OIL SOON message displays, have the engine oil and filter changed within the next 1 000 km (600 mi). If driven under the best conditions, the engine oil life system may not indicate the need for vehicle service for up to a year. The engine oil and filter must be changed at least once a year and the oil life system must be reset.... Reset the oil life system when the oil is changed.

Yep Engine oil/filter is ONLY dependent on the OLM. It considers, total engine revolutions, miles, and things like the oil temp after cold starts. If it doesn't get hot enough long enough to evaporate much of the water of combustion it will form things like sulfuric acid that eats metal when parked it will shorten the 12 month max time it allows to a lower number.

Yep foolish it makes you hunt thru pages and pargrapghs to find the requirements. Then did you miss something! My 2020 C8 had the same maintance table as in my prior 5 Vettes. That s what i read 1st. One page and another of notes! IMO GM< was foolish to eliminate those pages and make you hunt and winder sis I miss something!


BTW, this is from my 1993 Vette Owner's Manual before the Oil Life Monitor. Under conditions some Grage Queens are used it says change oil every 3 months or 3000 miles. And some wonder why they are required to change in 12 months or less. The OLM will put a message on your dash at ~10% life left. Can't miss it in any C8 as every time you start the car the message appears AND YOU MUST PRESS OK TO DISMISS! Yep your changing NOT that that oil is worn out it's for contamination and additive depletion.

 

DCT external canister filter replacement: Must be replaced between 7000-8000 miles on the odometer even if done earlier, then at 22,500 miles on the odometer, then every 22,500 miles after that, or every 24 hours of track use, or when the change transmission filter soon message, whichever is first. It is not required to change the fluid at the same time , unless the conditions for changing the fluid are met. Other than the 24 hours of track use, there are no time requirements on changing the DCT external canister filter.

Transmission Fluid Replacement: Must be replaced when the change transmission fluid soon message appears, or every 45000 miles, or at least every three years (regardless of miles) or every 24 hours of track use, whichever is first. The fluid life monitor does not include the three year requirement, so the owner must observe that requirement. It is not necessary to change the filter at the same time unless the conditions for changing filter are met.

Engine OIl and Oil Filter: Change it when the Change Engine Oil Soon message appears, or at least once a year (regardless of mileage). The one year requirement is built into the Engine Oil Life System. Never go beyond 7,500 miles or one years from the last engine oil change.

 

I agree. I will admit that I rarely looked at my Corvette owner's manuals before I bought the C8. Since it was a mid-engine car with the DCT transmission I spent a portion of two days after I picked up my C8 reading through the manual and was very happy to see that maintenance table. Maybe Chevy sent out the clarification letter on this very topic because they realized people weren't reading the manual?

 

I took my 2022 in at 36 months/13,000 miles for DCT fluid change and the Corvette specialist at Reeder Chev in Knoxville sent me away. His reading of the latest GM letter says was due at 22,000 mi, no calendar limit. Sorry to beat that dead horse again but…

 

he is wrong. Find another dealer or just tell them to do it. You’ll own the warranty issue if one comes up.

 

My DCT filter was changed at 5,400 miles and the fluid and filter were both changed at 16,000 / 3 years. My car hasn't turned into a pumpkin yet.

 

So, the "Corvette Specialist" read the letter, including the attached statement in the letter, and concluded that the fluid need to be changed at 22000 miles? Wow [insert twilight zone theme song here].! And, nowhere in the letter does it say change fluid at 22,500 miles. That's just stunning!

In this case, the "dead horse" isn't so much about the required maintenance, but simply an additional data point regarding the fact that many dealer reps do not interpret the letter (and apparently not the Owner's Manuals either) correctly.

 

Based on my made up assumptions about filter loading - you could probably go to 18300 miles if the first change was at 5400. I'm not recommending that.

While its not compliant with the stated maintenance schedule, my conservative analysis of filter loading, which is based on the specified first and second replacement intervals (7500, then 15000 to the next change at 22,500), says that if the you change the filter early, during the 7500 mile break in period, the second filter change needs to be at an odometer reading of

Miles (2nd change)=(2*Miles (1rst change))+7500miles

This is only for an early change, and you can see if its changed at 0 miles, it says the next change is 7500 miles. If changed at 7500 miles, the second change is at 22500, as expected. So, for a 5400 mile change, from a filter loading point of view, it says 18300.

This is still conservative, and based on the break-in filter loading rate falling off in a linear way between 0 and 22,500 miles on the odometer. In reality, it probably falls off exponentially - but we do not have enough information to model that. My recommendation and personal plan is to follow the schedule.

 

READ THE OWNERS MANUAL!

The answers to all of these questions can be found there.

 

Find a new dealer. Just do it. Then send a letter to the dealership's owner telling him his incompetent service department just lost him a customer.