Besides cost and a little less gas mileage does adding the 2 extra quarts on a Z51 only used on the street

1. have any benefit, ie, better shifting etc?

2. have any negatives

 

Depends who you ask, so get ready! Those who have it added are typically glad they did, and those that don't will bounce up & down telling those that did what idiots they are and how they're wasting money. I personally had it added by my delivery dealer and my transmission has given me no issues in 2 years/16k miles. At the 3-year mark when I'm due for the DCT fluid/filter change I'll be adding the 2 qts again. Because why not? To answer #2, its not hurting anything and can only help. GM opted to cut costs and save a few bucks because it "should be good enough..." but I'd rather not take that approach, personally.

Similar to how an axle/differential manufacturer (DANA) will call for one fluid weight in their spec, while the vehicle manufacturer (JEEP) will call for a lighterweight fluid in the factory spec. Why? The vehicle manufacturer cares about EPA ratings and getting the vehicle through the warranty period. The component manufacturer cares about neither and wants their product to be as durable & robust as possible.

 

Lower fuel economy. ... As I understand it, (that's very limited knowledge as a given) the reason for adding the extra is that without it, under sustained cornering, the tranny won't be completely lubricated.

 

I did it.

Zero benefit for daily driving

It's possible you could get a half mile less per gallon. I'd have no inclination to try and measure that

 

I haven't experienced any loss in gas mileage, but low speed shifting in traffic did improve. I like to drive hard on windy back roads and plan on tracking soon it just made sense for me.

 

Tadge said they don't add the extra 2 liters to all cars because it has a small impact on fuel economy, and to a manufacturer small differences can mean a lot. Other than that, the only negative I've seen is the cost of having it done the official "GM" way. if you can do it yourself by jacking up the drivers side of the car, then the cost s pretty minimal.

Any advantages? If you drive hard on the street, or do any kind of track driving, even just lead - follow laps, I think it's cheap insurance. A couple of GM guys from the DCT program were at Carlisle a couple of years in a row, and they said they would recommend it for cars driven hard on fast, twisty roads. GM officially says not needed.

I put it in mine using the tilt method before going to NCM to do some lead-follow laps on the track there. My DCT is still fine at 18,000 miles. It would probably still be fine if I hadn't added the extra, but like I said, it's cheap insurance and gives peace of mind.

I'm not sure I would have paid $500 or so to have a dealer do it, however.

 

The solution to pollution is dilution. I'll be adding 2 liters when I change the motor oil at 2500 miles. I like to change oil at 5K intervals and this should get me on that schedule with the 7500 mile free fluid change and DCT filter replacement. I'm inclined to dump the DCT fluid at 2500 miles as well and most likely will. For me it's just time and the cost of the fluids. Peace of mind.

 

I only drive on the street albeit occasionally aggressively like hitting high "g" turns. Never have seen any evidence I should add and some good reasons I shouldn't.

The best we have is a semi formal comment with reason from a GM person at seminar in Carlisle PA. He said it's needed if Tracking and going downhill and turning. That could cause the fluid to go toward the top of the case. Assume that means the fluid could leave the bottom of the case where the oil pick-up is located. So IF Tracking at Laguna Seca Corkscrew Turn OR is Jumping your C8 might be an issue.

Also it's obviously an after thought OR Teemec would have:

• Not put the fill/check level plug where it's useless after two quarts are added. Could have put 2 plugs IF it was thought needed.
• They would have put the fill plug where you add a foot back where it could be accessed by simply removing a plastic plug in the truck bottom. (NOT taking 2+ hours and many parts off!)

Also gear trains DON'T operate as well with more fluid. It just creates drag and possible oil foam.

See no logic for adding for street driving. Believing it runs better is not supported technically. Recent proof is the C8 Z06 with a slight mod on the lower pan DOES NOT REQUIRE ADDING THE TWO EXTRA QUARTS EVEN WHEN TRACKING. THAT IS EVEN WITH CUP 2R TIRES THAT CREATE A HIGHER MAX LATERAL "g" FORCE.

Here are some pics to help understand the issue:

May have been some last minute testing at Laguna Seca where they found creating the hill before the Corkscrew where you make a shape downhill turn caused an issue. So if Tracking add.


Chuck, Conti dealer Tech during his video of 2 to 3 hour effort adding the 2 quarts shows where they could have put the fill plug, under the truck! Have to take a lot apart to add!


Gears don't need high level for lubrication. Just creates drag. Lubrication is created by Lub being sprayed all over the case. Pic from doc showing level needed for various gears.


Banks engineer showed in a video what lubrication looks like at moderate speeds. They found foam forming and air bubbles in fluid REDUCE lubrication ability.

Perhaps the most compelling reason is this Tech who has torn 50 DCT apart. He states a number of times in the video NOT to add if NOT TRACKING

 

The Z06 has “essentially” the same DCT and it comes with the 2 extra liters. I don’t believe the foaming or drag issues within the DCT are an issue with our DCTs. I truly believe that the extra almost 20% more fluid will help in keeping the debris spread out within total volume of fluid within the DCT. Very cheap insurance for the prices of 2 liters. Easy to do yourself. Your car, your choice

 

Yes there should be no discussion about foaming as this extra 2 liters is actually specified by the manufacturer for track use. The manufacturer would absolutely never specify an overfill condition that would cause foaming and subsequent failure... particularly not for track use.

 

Do you have the DCT fluid fill capacity for the Z06 DCT? I've looked but haven't found it. I have seen statements that the Z06 pan baffles have been redesigned so that the additional two quarts isn't necessary for track use.

 

I don't and can't find the specific amount of DCT fluid for the Z06. The owners manual says it's not required to add an additional 2 liters for the Z06. Same with the Track Prep Guide. I believe you are correct with respect to the redesigned pan. I'm under the impression (perhaps erroneously) that the DCT in the Z06 has the additional 2 liters. If the fluid issue with the Stingray could be addressed with a pan design change one would think that they would have incorporated that into the Stingray's pan.

 

I've heard rumors that the 2024 Stingray won't requrie the additional 2 quarts of fluid. It's possible that the pan baffle redesign requires a different case casting and they didn't want to roll in a different case into the Stingray until it was convienient.

 

1. Opinions aside GM (and we even heard Tadge) say to add two quarts if tracking the car. They didn’t say to also add two quarts to improve non-track performance or improve street driving experience.

2. Negative is to pay for something that’s not required or needed unless it simply makes you feel better.

 

Not what Harlan Charles said in a Video. IT DOES NOT COME WITH THE TWO EXTRA QUARTS. Yep you can actually use the fill/check level plug and don't have to take the car apart to add two quarts every time you drain fluid.

Proves that the ONLY reason for the extra two quarts was a last minute find before the car was released. It's as the fellow in Carlisle seminar said (see my prior post.) They changed the Z06 bottom trans pad so if creating the hill in the Corkscrew at Laguna Seca and turning the fluid will stay under the oil pick-up! It's not and probably never was for high lateral "g" force as the two quarts are NOT NEEDED for the Z06 even with Cup 2R tires!

Having more fluid to keep debris disbursed?? Debris is to be caught in the filter.

Quoting another GM Person:
In the Z06 reveal, Aaron Link (Global Vehicle Performance Manager) speaking w blogger Speed Phenom, who asked:
“do we still have to add 2 extra quarts of trans fluid?”
Link replies: ‘No, there is no need to “overfill the transmission”. ‘On every track we have run the transmission performed well and confident no need for additional oil.’

My note: His word OVERFILL. That is what is happening if you add two quarts to a C8 and are not Tracking!

Sorry But reminds me of this graphic I use when discussing MIG shielding gas flow with engineers and fabricating managers.

 

The words "over fill" should be taken into context. If the trans was considered truly over filled with the 2 extra liters, GM would have said to remove those 2 liters after tracking for everyday driving. GM says no need so it's not "over filled" in the negative context being described. Again, your car, your choice. I'll be adding the 2 extra (because of the occasional track events) but mostly for what I perceive as the benefits of having the additional fluid.

 

I've seen this idea posted before, and I am having trouble pulling the thread on how this would work. I believe that within a very short time, every drop of transmission fluid gets pumped through the filter regardless of the volume. The only debris that should be left to be "diluted" would be something small enough to pass through the filter. Is that what you are thinking about? Also, every drop of fluid from the pan that goes through the valves, goes through the filter first. Again, the only thing that should get to the valves from the transmission pan would be something that can pass through the filter. Seems like the only debris that can clog the lines and valves would be something that originates downstream from the filter - unless there is flaw in the filtration flow.

 

The logic of not removing after Track Events is because it's unlike racing brake fluid that GM recommends for Tracking and say remove after for standard fluid has to do with it being more Hygroscopic- (it picks up water more readily.) Brake fluid can tolerate some water but after an excess (relatively low percentage) the excess water causes water vapor (steam) when braking hard. Water vapor is compressible and oops foot goes to the floor!

The extra DCT fluid is not dangerous, more drag and other possible issues but safe. IF you Track you should add as GM says to in the Owner's Manual.

BTW, bet they tested at the Corkscrew in Lagina Seca! Climbed that hill many times to watch my friend crest the hill in his ~1600 lb Maserati Birdcage!

Aaron Link replies to question of extra 2 quarts in C8 Z06: ‘No, there is no need to “overfill the transmission”.‘On every track we have run the transmission performed well and confident no need for additional oil.’

Have this Pic I took of friend Tom in his Maserati Birdcage (one of 40 vintage -mostly old race cars- he owned) in the Corscrew at Lagunes Seca. Tom was born same year as I, 1942. September will be 13 years since his untimely death. Pic is on my Man Cave wall.

 

We don't know what's causing solenoids to get fouled or the other issues that are causing early DCT issues so I am only speculating that there is debris (from the clutches) that is getting to places it shouldn't even with the external DCT filter. But we've seen some DCT fixes via the flushing of solenoids via the GM process which seems to confirm contamination. If the filtration system were adequate there wouldn't be debris in places it shouldn't be. Can we assume that the fluid coming away from the clutches see the filter before seeing the valve body and solenoids? If it doesn't Tremec screwed up in my opinion. I don't know what the micron rating is for the sump filter but suspect that that filter is not the one that's trying to keep clutch debris out of places it shouldn't be. I'm more concerned about the stuff that's smaller than the micron rating. With more fluid in the DCT, the percentage of contaminate to volume of fluid is lower (we've got 15K miles post first filter change where the clutches will continue their normal wear. Those wear particulates will end up somewhere). Will the rate of contamination "build up" be lessened with this lower percentage? I don't know. But my supposition is that once debris starts to collect in places it shouldn't, more debris will end up there (dirt attracting dirt). Cleaner surfaces and passages tend to stay cleaner than ones that have build up. Very true with dead end passages and such. Again, without seeing the tear down of failed transmissions and the actual causes of failures it's unknowable to the community. I'm also curious to see if the DCT fluid temps are lower with the extra fluid. It'll take longer for the fluid to get to temp, just don't know if that temp will be lower vs with the original fill volume. When I dump my fluid at around 2500 miles I'll attempt to check for silt in the fluid by running it through a filter. If there's no silt seen I'll have more confidence in the external filter. Will be a learning experience in the next few years. I will share what I find. Or don't.

 

I wouldn't expect stabilized fluid temperatures to be lower and it is possible they could go higher. A gear bath transmission is designed with an optimal fluid level which is a compromise between competing requirements. A high performance design would have a dry sump system similar to an engine dry sump system to keep the gears out of the fluid. The higher the fluid level the higher the loads on the gears and bearings which can cause increased fluid temperature and parasitic HP loss which is likely the reason the fuel mileage goes down.

Early in my career I was the manufacturing engineer responsible for the overhaul and testing of gearboxes capable of transmitting power from a 5K HP turbine turning at 25K RPM. These gearboxes had a dry sump lubrication system with a filter, cooler, and pump pressurized lubrication system delivering fluid to the bearings and nozzles spraying fluid on the gears as they came out of mesh. Occasionally during testing we would encounter "flooding" where the scavenge system got overwhelmed allowing the fluid level to reach the gears. We monitored bearing temperatures during testing and the flooding was evidenced by a sharp increase in bearing temperature caused by the additional load from the gears.

When the C8 engineers discovered the fluid starvation problem during high G events they likely determined that adding additional fluid was the least of the evils at that point. More isn't always better.