Hello, I have a question about my C8 DCT and come July it will have 3 years on it but I'm thinking come next month I will be at 7,500 miles so I'm planning on changing the engine oil & filter and the DCT oil and filter. There is so much talk about the DCT service that I'm trying to get a better plan together. Should I go ahead and change both now and save a little time & money or do the DCT filter now and again at the 3 year mark????

 

If it was me I would ask your dealer if they are going to charge you full price for both the DCT filter service and the drain and fill if you do them at the same time. The reason is that 95% of what they need to do during the DCT filter is what they will do for the drain and fill so they should severely discount them done together.

If they will discount them together I would then wait until you have closer to 8000 which will be closer to the July 3 year point.

If they won't then other than not having to go in twice it really doesn't matter.

When is your engine oil and filter due? Is that now or closer to July?

 

@C8CorvetteZ51

Per the service bulletin recently sent to C8 owners, GM wants all transmission oil filters replaced between 7,000-8,000 miles. The owner’s manual states 7,500 miles, but GM gives a leeway of 500 miles before or after that mark.

The next change comes at 22,500 miles and then every additional 22,500 miles afterwards.

As far as the years, it should be done at 3 years regardless of mileage.

Given what you said in your OP, you should just get the service done now and not worry about the time interval since you are already at the mileage point.

A key point here is if you had your transmission filter replaced prior to 7,500 miles, it still needs to be done again between 7,000-8,000 miles.

 

Both if you can.

The fluid can be changed at three years or less. The filter can be changed between 7000-8000 miles. Make sure you don't go more than 3 years past the in-service date. In my case I checked the start date for the warranty and it was a couple of days earlier then the date I paid for and took delivery of the car - so I made sure I changed the fluid less than three years from the recorded warranty start date. Once you have verified the three year mark, change both in the 7000-8000 mile window, but before three years. In my case, I got to the three year mark and did not have the minimum 7000 miles, so I changed the fluid only.

 

I know you know this but what you wrote could be misinterpreted. You said "all filters". There are two filters in the DCT, and internal pan filter and an external cartridge filter. The internal one is considered lifetime and not a maintenance item. The external cartridge filter is the on that gets changed per the maintenance schedule.

You said "as far as years..." this is not for the DCT cartridge filter it is for the drain and fill of the DCT fluid.

Again, I think both people, you and the OP, understand this but it could confuse others that read the post.

 

Since you’ll need an oil change and the DCT filter needs changed at 7500 miles that obviously will need to be done next month. If you want to make another visit to the dealer in July for the transmission fluid that would be your decision. I’d personally just get it all done at once next month. Then you wouldn’t need another trip to the dealer until next years oil change.

 

Thank you. But “all transmission oil filters” is a direct quote from the bulletin and only refers to the external filter. The fluid and filter are changed at 7000-8000 miles or three years.

I understand your point of clarification, but most owners know that the filter in question is the external filter. Those that don’t know that are likely not the type to do the work themselves and the service department will already know which filter is the one that requires changing.

 

No, the DCT filter and fluid are on separate schedules. Filter is not three years and fluid is not 7-8000 miles.

 

From personal experience, when they change the filter, the fluid usually also gets changed as it is usually close enough to have to do both. Not saying you are wrong because you are not, but it almost always works out that way. Especially if you actually drive the car (my Vettes are daily drivers).

 

Okay, but again, putting out info contradicting the manual and the paper GM sent out does nothing but confuse people. And as you know there are a lot of confused people.

 

The paper is pretty clear as is the manual. Thank you.

 

I agree. Get the trans filter replaced between 7000 and 8000 miles and the fluid replaced every 3 years. If the filter mileage and 3-year fluid change happen to intersect, get them both done at the same time. Sounds pretty simple to me.

 

My point to the other member is that changing the filter and the fluid simultaneously is how things tend to line up without regard to the interval difference. I know that there is an interval difference between the DCT filter and the fluid needing to be changed, but if you daily drive this car and/or do a lot of long road trips, the likelihood that you will be changing the filter and the fluid at the same time goes up. I know this because that was my experience with my 2022. The oil life monitor for the transmission fluid is your proper guide for changing the fluid. With regular use, you will wind up changing the fluid and filter simultaneously in most cases.

 

While the motor oil life accounts for time, the 1 year requirement the DCT fluid life does not. My manual says to check the DCT fluid life percentage every 45k miles and change if needed. The note says or every 3 years.

My 2020 also happened to need the DCT filter and fluid at the same time but we have to be careful what we say as there will be people that said "but the experts on the forum said..." Bottom line, different services with different time/ mileage requirements.

 

Bottom line up front:

The miles per year where it is possible for the DCT filter and fluid replacement events to be coincident at the three year mark is between 7167 miles per year, and 7833 miles per year. Outside of that, with a lower miles per year the three year event will happen before the filter needs to be changed, and above 7833 miles per year, the filter will need to be changed before three years. This considers a +/-500 mile tolerance on the first and second filter change.

The nominal odometer readings for the filter changes are 7500, 22,500, then every 22,500 miles after. The first interval is 7500 miles, the second interval is 15000, all subsequent intervals are 22,500 miles. The tolerance on the first change interval is +/- 500 miles. I am going to assume that the tolerance on the second change is +/-500. For subsequent changes the tolerance on the interval is one side – less than 22,500 miles and not more.

The nominal intervals for fluid changes are at least every three years or at least every 45000 miles. I am going to assume that the tolerance is one sided – less than or equal to three years or 45000 miles and not more.

With these conditions and assumptions, what miles driven per year would result in the filter change and fluid change being aligned (or coincident)?

Certainly 7500 miles per year would result in perfect alignment. At year one the filter is changed. At year three, with 22,500 miles, the filter and fluid can be changed.

What about less or more miles per year? To figure that, the tolerances need to be considered (in my view). Compare three cases – the most frequent filter changes, nominal filter changes, and least frequent changes like this:
So, this table shows that if the filter is changed at 7000 miles and then 14500 miles later the mileage at the second filter change will be 21500. If the filter is changed at 8000 miles, and then 15500 miles later, the mileage will be 23500. To coincide with the three year event, the corresponding miles per year must be between 21500/3=7167 and 23500/3=7833.

So the miles per year window where its possible for the 2nd filter change to coincide with the three year event is 7167 to 7833. Pretty narrow. If the mileage exceeds that, the filter will need to be changed before the three year mark. In those cases, its acceptable to change the fluid too, if one wants to do that, so yes with higher mileage the filter and fluid can be changed at the same time, but will result in early changes of the fluid - sooner than three years. If the mileage is less than 7167, then the three year will be reached and the fluid must be changed before the filter change is required. Can the second filter change be early? Maybe. But the service intervals do not align.

 

The bolded is what I have been saying all along.
My real-world experience with my recently traded 2022, which had a tad below 30k miles on the odometer, aligned where it was prudent to change the filter and the fluid together. Yes, I had the fluid changed early, but the OLM was in the teens, so I thought it prudent to have the tech change them both.

As to your question, I preface my answer as an unofficial opinion based on the letter GM sent; it seems changing the filter is the more concerning part of this from GM's perspective. It is why the letter states, "If you had your transmission filter replaced prior to 7,500 miles, it still needs to be done again between 7,000-8,000 miles.

It seems that some folks are trying to avoid having to pay to have the fluid and the filter changed simultaneously. I get not changing the fluid unnecessarily, but I let the OLM dictate when I need to make a change, and the mileage GM set is my cue to change the filter. If I hit the mileage for the filter and I am close (30% or less) on the fluid, I will have the tech change both. YMMV.

 

Thanks! At first, I did not know what question I had asked - but I see it was what I intended to be rhetorical. " I said "can the filter be changed early" Maybe." But the context was the 2nd filter change, not the first one (or the first required one anyway). The first required one must be between 7000-8000 miles. The question was meant to be with respect to the second filter change at 22,500 miles. If it was changed at 7,500 miles, and again at, say 15000 miles, is it ok to go a full 22,500 miles before the third change? We know that when the filter is changed at 7,500, the next change is a mere 15000 miles later, whereas all the later ones are 22,5000 miles. It has been suggested, by me and others, and purely speculation, that the second interval is still short because there is still some extra break-in debris being shed between 7,500 and 22,500 miles. If that is true, then changing it sooner, say at 15000 instead of 22,500 miles and going a full 22,500 miles for the third change might be a problem, if there was additional debris still being generated. So, the "maybe" is because I do not know. And, since I don't know...........

My own plan is to make sure I change it near 22,500 miles, so I don't have to give it further thought. I have already changed the fluid, but still dont quite have the minimum 7000 miles for the filter. But I will change it between 7000 and 8000 miles, the again near 22,500 miles, making sure its no more than 15000 miles (give or take a little) from the previous change. The next one, and everyone after that will be 22,500 miles or less from previous one.

 

@Andybump

In the close to three years I had my 2022, the filter was changed three times and the fluid twice.

The first time the filter was changed was just after I brought the car home from Bowling Green due to a CEL. The second time was when the valve body was the replaced after the dreaded “idle creep disabled” CEL happened. The fluid was changed along with the filter. The third time was when I hit 7330 miles. My transmission fluid was at 19%, so I had them change the fluid as well, added the two extra quarts for track prep, that the 2024s and newer models no longer need.

For the good of the group and not you:

To directly address the interval for changing the filter after the first change at 7000-8000 miles, the next change comes at 22,500 miles and then every additional 22,500 miles afterwards. This is per GM’s letter/bulletin.