I have a htc 2022 l2 and noticed some interesting things on changeing fluids..
There are 3 things to watch....
1. oil and filter change...thats straight forward..millage or 1 year
2.dct filter change at 7500 miles...some are getting their first oil change and pay themselves and do the free service which changes the trans filter as close to 7500 miles or 2 years..Since you now have 2 years to get your free 1st service.l.
3. The trans fluid...at 3 years or 45000 miles..
Now the issue for me since I drive very little, like 5000 miles a year and my filter change will not match up to that millage.or time for the fluid change..;so my question is do I need to change the filter when I change the trans fluid or wait till the filter is due?? ..
The way I read the manual is to change filter if you are close to that but you could wait..so you might change fluids and not filter until it reaches the correct millage..They want you to get as close to 7500 miles as you can. I saw a vid that says they might have an update soon that not only follows oil life, trans life and TRANS FILTER...
Your thoughts..

 

^^^
My decision was simple as IMO your's could be. Last August when my 2020 with ~3500 miles had 5% life left on OLM. Did I wait for Year 2, then year 3 change 11 quarts of DCT fluid and leave the 1 year old filter in and ~8 oz of dirty fluid? Nope had engine oil & DCT filter AND DCT flush (per GM requirement when changing filter) done all on GM's dime. Year 3 will have the DCT fluid changed as required AND a new filter (with ~7000 miles on my current ~1 year filter) and no dirty fluid left in filter holder.

SIDEBAR
My other reasons were:

1. Many forum posts re DCT CELs where a flush was recommended and solved the CEL issue.
2. My observation that for the first ~800 miles when crawling below ~4 mph and 1st gear clutch slipping it was slighlty rough. Now smooth as silk so the multiplate clutch wore in! Keep in mind every time you stop at a red light etc that 1st gear clutch is slipping.
3. I made that decision last August BUT recently at a Bash a forum member attended a C8 maintenance seminar, and the GM Rep said change the DCT filter at the 1st engine OLM required change. Yep with DCT issues I good precautionary move.

From a cost standpoint changing the 11 quarts of DCT Fluid labor is removing the 20+ bolts from the rear aluminum aero panel and some on the panel in front. Once done the extra labor to remove the 4 filter bolts is trivial. Can buy a filter kit on the Net for ~$125 wholesale IF YOUR CHEAP!

 

First things first.
The word is mileage.
I think the 2023 C8's have a gauge for a DCT filter notice.

I would not change the Trans fluid without a filter change. Does anyone know if GM has a requirement for the transmission flush at each filter change?

 

THmm, reminded of some folk's decision making. Think for now and forget you'll be forced to do something FOOLISH in year 3!!

Nope changing the DCT fluid year 3 is a requirement based on time NOT mileage! Yep, my 2020 has a DCT fluid life indicator like the 2023. It's unlike the engine OLM, does not consider time. How do I know? It's almost year 2 and with 6500 miles it shows 78% life left. But next August my 2020 and the 2023 Owner's Manual say ALL DCT fluid must be changed no later than every 3 years!

 

My thoughts: The manuals, both the 2021 and 2023, list multiple triggers for checking and/or changing engine and transmission fluids and filters, both in the Oil Life Monitor sections and the Maintenance section. I think the 2022 manual is the same as the 2021 manual for recommended service, but did not check that. The 2021 manuals shows the service required in a chart, with notes. The 2023 manual omits the chart and notes, and has text instead. The 2021 manual has separate charts for "normal" and "severe" service, but they are identical. The 2023 manual specifically says the severe service is the same as the normal service requirement. The 2023 model adds a transmission fluid filter life monitor that the prior model years do not have. I believe that requirements are mostly the same, but there are a couple of differences. Also, there is some controversy over whether the external transmission canister filter must be changed whenever the transmission fluid is changed. Both manuals currently say that when you get the "change transmission fluid soon' message to change both the fluid and the canister filter. But there is some speculation that this may be an error, because there is other wording the manuals that seems to imply that the intent was to allow the fluid to be changed without changing the canister filter. I have attempted to summarize what the manuals say about the fluid checks and changes in a table - attached below. In this table, I have represented it the way the manuals say it - which includes changing the trans fluid canister filter when the "change transmission fluid soon" message is received. I understand it appears needlessly complex, but it just illustrates what the manuals say. It could, and should be simplified, and clarified, by GM. Please advise if there is an error, where the table does not correctly reflect what the manuals say.

 

I agree the DCT fluid and filter change information is very confusing and needs to be clarified.

1) My 2020 manual has multiple places where it calls out the canister filter change is strictly related to mileage and no time element is mentioned. However, there is one place under the transmission fluid change heading that says to change the canister filter when the transmission fluid monitor says to change the fluid. If you go by the number of times the canister change based strictly on mileage is referenced in the manual then mileage wins.

2) There is also a filter inside the DCT. Does a fluid change require the pan to be dropped and the internal filter changed also?

3) The requirement to perform an internal DCT hydraulic system flush prior to the canister filter removal was instituted after delivered cars were having DCT problems. The direction to do this is only visible in the online instructions the tech sees when performing a DCT canister filter change. Is this now required anytime the DCT canister filter is replaced? Or is it only necessary for the first canister filter change at 7500 miles to remove residual contamination and bread-in debris?

 

There was a more in-depth discussion of this on the other forum. The context of the statement was to not skip the DCT canister filter change at 7500 miles. Some people were changing the canister filter very early. The recommendation was to replace the canister filter again at 7500 miles if the canister filter was changed early.

Here is the post that started a long thread. Note that this was prior to GM announcing that they would extend the compensation for the first service to 2 years:

I was at Corvettes at Carlisle today, and there were a couple of presentations by GM personnel that provided some useful information, and cleared up some confusion or misconceptions.

First was a presentation by two people introduced as the program manager for the DCT project and another identified as the Assistant Chief Engineer for the DCT. Both are GM employees, not Tremec. They emphasized the importance of doing the DCT filter change at about 7500 miles to ensure all the break-in wear products are removed. Wear products that continue through those first 7500 miles, no matter how long it takes to get there. The key point was that if you put few miles on your C8, and take advantage of the "free" filter change in the first year with only a few thousand miles on the car, you should change it again at 7500 miles to remove the wear products that accumulate after the early change.

They also emphasized the importance of adding the extra 2 quarts (yes, I know it's actually liters, but even they said quarts) if you "are tracking the car." They said in something like a fast down hill turn, the oil can actually be lifted into the top of the transaxle, causing the oil pick up to suck air. I asked them to define "tracking." Does that include a few lead / follow laps at NCM, or HPDEs, or only if you're near racing speeds?

Their answer was two-fold: First, that they think GM is changing the wording of the recommendation to "tracking or spirited driving," and second, that they would define track use as anytime the car is on a track, even lead-follow laps. I think there's been a general consensus that a few laps at far lower than racing speeds doesn't really need the extra oil. This advice seems to contradict that.

(Don't argue with me - I'm just the messenger.)

They also said a replacement DCT, out of warranty, costs $20,000!

Next was a gentleman named Paul (forgot his last name - sorry) who is the manager who deals with customers or dealers when someone is seeking an accommodation for a problem / repair that is outside the warranty. The bulk of his presentation amounted to "follow the recommended maintenance and the OLMs." He also recommended letting the dealer do the DCT filter change, because the dealer tech will (a) first do the DCT flush procedure to remove as much wear material from the oil as possible. Also, after the filter is replaced, the tech will do a pressure test to ensure there are no leaks. Neither of which can be done at home without the GM software.

I think this eliminates any question about whether the flush is part of the filter change procedure or not.

 

I did an intial engine oil and filter change at 1500 miles.

I just had the first free maintainence after 14 months of ownership and 6200 miles which incluced the engine oil and filter, DCT filter and DCT fluid top off.

My next engine oil change will be 1 year or when the oil life has less than 10%, whichever comes first.

My next DCT filter change will be in 22,500 miles from now or at 3 years of ownership I will have both the DCT oil and DCT filter changed or when the DCT fluid life is less than 10%, whichever comes first.

 

The OM has this footnote for DCT fluid changes:


That implies to me that if the filter is not due for replacement, you don't need to change it. BUT, it will be cheaper to replace it when they already have the lower panel off and the car on a lift than to do it later, so you might consider that.

Also, would you change your engine oil and leave a dirty filter, with dirty oil in it, installed?

 

For me, my fluid replacement interval will be based time, not mileage. I will be able to make it to the 2nd fluid change before mileage dictates that I replace my canister filter again.

It used to be a common requirement that an engine oil filter only needed to be changed every other oil change. But since engine oil filters are so cheap it made sense to go ahead and change them both while you were there. This isn't the case with the DCT canister filter. If the intent of the DCT canister filter change is strictly based on mileage then the engineers have already considered the residual dirty fluid in the canister. And that fluid is only about 2% of the total fluid volume. And the 3 year fluid change is probably conservative to begin with.

 

And the potential conflict with the other instruction - to change your trans oil and external canister filter when you get the "change trans fluid soon" message may not arise. No one has reported actually getting that message at the three year mark based on time, and JerryU reported that the decrease in percentage, at least so far, does not appear to include a time factor. And, you do reset that when you change the fluid.

I should add that the "Change Transmission Fluid Soon" message is mentioned 3 time in each manual. In two of the three, it says only to change the fluid. Only one says change fluid and filter. This along with the notes (like note 4 mentioned above) that say when changing the fluid at the 3 year mark, change the filter if the mileage is near the canister filter replacement interval then change it, strongly suggests that the latter version of the statement is a mistake.

Here are the different statements:
2021 Manual page 93:


2021 Manual page 242:


2021 Manual, page 292


2023 Manual, page 94


2023 Manual page 249

2023 Manual, page 307

 

One thing I noticed above though, in the 2023 manual, in the statement in the 2023 manual that includes the fluid and filter, its actually a little different from the one in the 2021 manual - instead of filter it specifically says "external canister filter". So, it still may be an error, but not exactly a cut and past error. Someone intentionally modified it without realizing it was wrong (if it is wrong).

 

45,000 miles or 3 years....so millage is a factor like the filter at 7500 miles for dct and oil filters

 

That is a great point, and it is also where the 2021 Manual (and probably 2022) differ from the 2023 manual. The 2021 Manual says change the fluid "if needed" at the 45000 mile mark while the 2023 Manual say explicitly change the fluid and external canister transmission fluid filter. In the 2021 manual it looks like "if needed" means if the fluid life is less than 10% because at 45000 miles, you also change the filter, and in the chart the note 5 for the filter change says to check the fluid life and change it if less than 10%.

 

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It appears to me the 7500, 22,500, 45,000 miles are check points for a dealer tech. For example, the 2020 thru 2022 owner's manual maintanence tables AND the 2023 owner's manuals (no table) in words still say change all DCT fluid a minimum of every three years, regardless of miles. Just like when the engine OLM says change regardless of miles. So can't confound other time statements with miles as being confusing.

Agree at those dealer tech check mileage it says "check fluid life and if 10% life left change." Would be foolish to come back to the dealer a short time after.

 

Yes. It says all those things in the 2023 manual: 1) Change fluid and external canister filter Every 45000 miles (without caveat), 2) change fluid at least every three years (does not say filter too), 3) change fluid& filter when you get the message, 4) at every 22500 mile check, change fluid and filter if life is less than 10%. Again, I note, that at 45000 miles, and when "the change transmission fluid soon message", and "when the transmission fluid life is less than 10%" is mentioned, all say change the transmission fluid and external canister filter. I have not found where the three year requirement ever says anything about changing the filter - just the fluid. Following are all from the 2023 Manual:

Every 45000 miles:



When Change Transmission Fluid Soon message is received:



Change Every Three Years(nothing about the filter here):




Every 22500 Miles:

 

^^
I would agree with others that if you changed the DCT filter year 2 and had only 3 or 4000 miles more year 3 it may be a waste to change filter again. Although new filter and draining ALL dirty fluid when changing all other is preferred IMO.

That is why (in addition to GM now telling folks that at the last Bash) I suggest to have the engine oil/filter AND the DCT filter with flush done the 1st time the engine OLM says change needed ALL ON GM's DIME.

THEN if you want to change your own engine oil OR PAY a Dealer, do that year 2. In year 3 have all DCT fluid changed with a new filter!

 

The DCT filter change discussion has my head spinning a little, I'd like to see if we are on the same page. Let's say I only put 4500 miles a year on my car.
Year 1 and 4500 miles I get the DCT canister filter changed.
Year 3 and 13,500 miles I change the DCT fluid without changing canister filter.
Year 6 and 27,000 miles (22,500 miles on the canister filter) I change both the DCT fluid and canister filter.

The above would be in compliance with the intent of the manual, correct?

 

^^^
Yep think so. Only issue that has been raised is some GM folks have said MUST change filter with 7500 miles and some believe some extra material is still wearing. So year 3 you will have 9000 miles (13.500 - 4500) on that filter changed at year 1. Would not be a bad idea to do another with the fluid replacement. BUT after only when mileage dictates.

 

Yea, that was a concern of mine when I had my filter changed at 4600 miles. But GM folks said their concern was with people changing their filter after a "few" thousand miles and then not changing it again at 7500 miles. I'm considering 4600 miles more than a few thousand.

And GM hasn't specifically stated why the filter needs to be changed at 7500 miles. The only logical reason is they are concerned about the filter being overwhelmed with particulates and bypassing before the regularly scheduled change. A properly designed and operating filter won't pass more particulates as it captures more contamination. I feel secure that changing the filter 2900 miles short of 7500 miles won't cause bypassing to happen in the subsequent filter.