gdb069

Note: I am not discussing the break-in issues just regular maintenance.
DCT Fluid change is at 45,000 miles and about average when I look at other DCT transmissions, although 911 is 120,000 miles or 12 years. However; the maintenance schedule for DCT fluid also indicates : Note (4) Or every three years, whichever comes first.
Many of us who don't track and have low mileage are coming up on three years. For me, changing DCT fluid (3 years) will occur at just 10,000 miles and seems like an unnecessary expense especially since the recommended mileage for someone who drives a lot and tracks may be 4 times what mine will be. Is the three year DCT fluid change far too conservative?

spireland

Three year interval for a fluid doesn't sound that aggressive to me, especially for a fluid doing something as important as keeping the transmission lubricated. Sure, it a daily it would seem excessive though not in a performance car.

JerryU

Thought someone said the Porsche DCT has separate fluid for the clutches. That could explain a reason for the difference. With the C8 DCT issues (although most minor) whatever the reason for change, depletion of additives (which can be time dependent) etc, would not skip that 3-year change that would be a good reason not to honor the warranty.

Andybump

I don't know. What I do know is there are additives in the fluid that apparently can separate over time. The instruction in the Service Manual say that quart/Liters containers of fluid "must be shaken to stir up the additives before pouring" into the transmission. Additives can deteriorate over time and that may be the reason for the change. I prefer to change fluids before there is any significant degradation, not when there is. That means that fluid (and engine oil too) will still be good when I change it. I will have 7500 miles a the three year mark, and will be changing fluid and the DCT filter at that time.

BIG Dave

My C8 will be three years old this November, right around when I expect my E-Ray to arrive. Therefore, I hope the next owner of my C8 (most likely the dealer) will have to deal with it, not me.

RKCRLR

The Tremec DCT in the GT500 allows 40K miles with no time limit and uses the same fluid. However, the transaxle is a different environment. We don't know why the 3 year interval is there but I'm going to assume there is a reason. Additionally, my understanding is the fluid containers have an expiration date.

Red Mist Rulz

I don't think anyone outside of GM can really answer that question. There simply aren't a bunch of older C8s on the road for anyone to experience what happens if you leave the fluid in there. GM does a lot of testing, though, including accelerated aging tests. Given the relatively high rate of problems with the DCT, I don't think I'd cheap out and risk voiding the warranty on the DCT in the event of a problem in the next 2 years.

JerryU

One difference from the 7 speed GT500 DCT is the ring/pinion loads. Is a pretty low viscosity fluid typically used for dif loads. Perhaps additives to handle that may have a limited life.

Red Mist Rulz

Tremec (via a Road & Track article) says the 2 DCTs have very little in common.

https://www.roadandtrack.com/news/a4...ission-issues/

RKCRLR

I agree the design details are different (the GT500 has to handle more HP) but I suspect the gear loadings, materials, bearings, syncronizers, friction materials, etc are similar. And I wouldn't be surprised if the clutch design is very similar. They are similar enough to specify the same fluid. The main difference is that the C8 has hypoid gears and LSD as part of the DCT. I suspect the difference in maintenace requirements is due more to the different engineering approach of the teams (Ford vs Chevy) than actual fluid/filtration requirements. What is curious is the time requirement on the C8 DCT fluid (same fluid as the GT500) and not on the GT500.

hawk02

I'm in the same boat as the OP. I will have roughly 10,000 miles on my C8 when it turns three years old in February. Assuming I continue with the approximate mileage every three years, my car will have four transmission fluid changes by the time the odometer reaches 45,000 miles. All on my dime.

Between the number of reported transmission failures and the cost of maintenance, I'm really learning to hate the DCT in my C8. It certainly isn't my favorite feature of the car, that's for sure.

C8gman

My 3 year mark comes up on 7/3/23. 8200 miles on the ODO. I just did a full fluid flush and filter yesterday. For me it's just wanting to make sure things keep running right and to avoid a possible denials of warranty if issues do arise in the next few years. Is it overkill? Maybe so. But with so many transmission issues out there I splurged for my own mental health.

jagtoes

My kids Audi A4 which has a DCT transmission requires a fluid change at 40,000 miles and no year requirement. This is a 2021 A4 Quttro. It will be interesting to see what the price is . The car just turned 32K miles so we'll find out early next year .

Kenny94945

I don't know concerning about 10K mileage in 3 years.

I could say that heat and running hours might be better indicators than time.

Then I'd ask, is the oil hygroscopic like brake fluid?
If so, time would be valid.
If the oil is immune to water, what about the case (above the oil level)?
Yes, the transmission is precise with many small/fine/ detailed parts in it.
Changing and flushing the fluid every 10K could be a good thing.

FWIW Good luck with your decision.

Andybump

Do you mean the hydraulic system flush? That procedure is part of the DCT filter change procedure. It is a computer manipulation of the solenoid actuated valves in the transmission, with the engine idling and wheel on the ground, with a goal of moving debris trapped in the lines and valve to the filter before the filter is replaced. That procedure does not involve draining and replacing fluid - except for topping off what was in the filter that was replaced.

No such thing as a fluid flush procedure for this transmission in the context of draining and replacing the fluid at three years - or anytime. (see attached clip from tech-link article).
And here is the link to that article:

https://gm-techlink.com/?p=12881

gdb069

Thanks for the responses. I would not worry about the "every three years" but the cost for 1Q is between $30 and $40 and it requires 11Q so possibly $400 parts and then a few hours labour. Still bothering me that there is a "date" base replacement of this fluid. Date base would imply some additive that breaks down, however a search of the DCT fluid brought me to here:
TR-9080 DCT 8-speed dual clutch transmission (tremec.com)
and that brought me to
TITAN FFL-4 | Automotive lubricants | FUCHS
and none of those applications using the same fluid have a date based expiry.
The only logical conclusion is that the Tremec TR-9080 has some weird component that requires an additive that breaks down faster or ...

JerryU

Hmm, doubt it's just a weird component!

I started investigating antifoam oil additives when the GM bulletin to change oil in dry sump C7s at 500 miles "because of silicone from curing engine seals depleting the antifoam additives in the engine oil causing oil foam" came out 13 months AFTER I got my early C7 Z51 in September 2013.

This is an extensive discussion of what additives do and that they deplete over time.
I was a bit surprised when I had my DCT filter changed in 2021 and the Tech was shaking the Liter bottle for quite a while before he filled what was removed from the filter and filter housing. I asked if that was commonly needed. He said yes with some transmission fluids and it warned it was needed to mix the additives in the DCT Fluid. This great Tech does everything by the book.
Lubricant Additives - A Practical Guide (machinerylubrication.com)

Being a "Techie" I read it all but know most are not so this is about 10% of what is presented (without pics) with some words in Bold I thought might be important for the C8 DCT:

Additives have three basic roles:

• Enhance existing base oil properties with antioxidants, corrosion inhibitors, anti-foam agents and demulsifying agents.
• Suppress undesirable base oil properties with pour-point depressants and viscosity index (VI) improvers.
• Impart new properties to base oils with extreme pressure (EP) additives, detergents, metal deactivators and tackiness agents.

It’s important to note that additives are also sacrificial. Once they are gone, they’re gone.

Particle enveloping means that the additive will cling to the particle surface and envelop it. These additives are metal deactivators, detergents and dispersants.

Metal wetting is when additives anchor to metal surfaces, which is what they are supposed to do. They attach to the interior of the gear casing, gear teeth, bearings, shafts, etc.

Additives that perform this function are rust inhibitors, anti-wear (AW) and EP additives, oiliness agents and corrosion inhibitors.

Whether they are enhancing, suppressing or imparting new properties to the base oil, additives play an important role in the lubrication of machinery. Remember, when the additives are gone, they’re gone, so don’t forget to check your additive package.

Types of Lubricant Additives: There are many types of chemical additives mixed into base oils to enhance the properties of the base oil, to suppress some undesirable properties of the base oil and possibly to impart some new properties.

Additives typically make up to 30 percent of the finished lubricating oil, depending upon the target application of the lubricant.

Lubricant additives are expensive chemicals, and creating the proper mix or formulation of additives is a very complicated science. It is the choice of additives that differentiates an oil from a hydraulic oil, a gear oil and an engine oil.

Some additives perform their function within the body of the oil (e.g., anti-oxidants), while others do their work on the surface of the metal (e.g., anti-wear additives and rust inhibitors).

Anti-oxidants: Oxidation is the general attack of the weakest components of the base oil by oxygen in the air. It occurs at all temperatures all of the time but is accelerated at higher temperatures and by the presence of water, wear metals and other contaminants.

They are sacrificial additives that are consumed while performing their duty of delaying the onset of oxidation, thus protecting the base oil. They are present in almost every lubricating oil and grease.

Anti-wear (AW) Agents: These additives are typically used to protect machine parts from wear and loss of metal during boundary lubrication conditions. They are polar additives that attach to frictional metal surfaces.

They react chemically with the metal surfaces when metal-to-metal contact occurs in conditions of mixed and boundary lubrication.

These additives become “used up” by performing their function, after which adhesive wear damage will increase.

Extreme Pressure (EP) Additives: These additives are more chemically aggressive than AW additives. They react chemically with metal (iron) surfaces to form a sacrificial surface film that prevents the welding and seizure of opposing asperities caused by metal-to-metal contact (adhesive wear).

They are activated at high loads and by the high contact temperatures that are created. They are typically used in gear oils.

Anti-wear additives and extreme pressure agents form a large group of chemical additives that carry out their function of protecting metal surfaces during boundary lubrication by forming a protective film or barrier on the wear surfaces.

Detergents: Detergents perform two functions. They help to keep hot metal components free of deposits (clean) and neutralize acids that form in the oil. Detergents are primarily used in engine oils and are alkaline or basic in nature.

Anti-foaming Agents: The chemicals in this additive group possess low interfacial tension, which weakens the oil bubble wall and allows the foam bubbles to burst more readily. They have an indirect effect on oxidation by reducing the amount of air-oil contact.

Some of these additives are oil-insoluble silicone materials that are not dissolved but rather dispersed finely in the lubricating oil. Very low concentrations are usually required. If too much anti-foaming additive is added, it can have a reverse effect and promote further foaming and air entrainment. (My Note: The reason I 1st investigated Anti-Foam Additives was my early C7 Z51 I got September 2013, 13 months BEFORE the GM bulletin that said change oil at 500 miles to prevent "silicon from curing engine seals under high-speed operation from depleting the antifoam additives and cause oil foam to go from the dry sump tank to the air intake and drip on the ground.' Note had nothing to do with debris AND was only for dry sumps NOT wet sumps that had no dry sump tank or hose going to the air intake.)

Friction Modifiers: Friction modifiers are typically used in engine oils and automatic transmission fluids to alter the friction between engine and transmission components. In engines, the emphasis is on lowering friction.

In transmissions, the focus is on improving the engagement of the clutch materials. Friction modifiers can be thought of as anti-wear additives for lower loads that are not activated by contact temperatures.

Tackifiers: Tackifiers are stringy materials used in some oils and greases to prevent the lubricant from flinging off the metal surface during rotational movement.

How Oil Additives Get Depleted: It is very important to understand that most of these additives get consumed and depleted by:

1. “decomposition” or breakdown,
2. “adsorption” onto metal, particle and water surfaces, and
3. “separation” due to settling or filtration.

For many additives, the longer the oil remains in service, the less effective the remaining additive package is in protecting the equipment.

AORoads

Jerry, thanks for the above. I doubt if everyone knows most of what's been written. I'll assume this is a first-rate tech paper on additives for cars. For that reason, you've highlighted by using both bold and italics on some sentences. I also think those sentence deserve an underline since they are "definitive statements" that anyone who reads this should know.

And lastly, I think the paragraph beginning with, "Lubricant additives are expensive...a hydraulic oil, a gear oil and an engine oil." should be highlighted the same way, italics, bold and underlined.

Maybe it's my own lack of knowledge but I think this was a valuable piece of work to read and understand. Thanks for taking the time!

JerryU

Thanks.
Yep put the link if anyone wants to read the whole article. As I said I probably abstracted 10 to 15% and no pics. I recall another article I found in 2014 when I had my 2014 C7 Z51 and that GM bulletin 13 months came out after I got my early car and subsequently GM required and gave a free 500 mile oil change! No such requirement when I had mine! That article said silicon can deplete the antifoam additives that are in most oil. This article added that silicon is used as an antifoam additive BUT too much can cause foam!

GM did say the oil foam was not a durability issue BUT under high speed driving could cause the foam to go though the hose (it was the burped air hose) from the tank to the air intake and flow down, soak the air filter and drip on the ground.

I added an aFe low restriction air intake and looked carefully for any signs of oil. Had none.

Kracka

Engine oil is date based, coolant is date based, brake fluid is date based. Why wouldn't transmission fluid be?