[CeeSeven]

It appears that the auto trans overheating issue is not a new one on auto Corvettes from other posts. But many thought it might be addressed in the C7, being a new ground up (almost) car. Well, it does not appear to be the case.

I've had the problem every track day from the get go (November '13). The manual says, "First time on track do not run the car as long or as hard or overheating could occur which may damage the trans and not be covered under warranty." Well, I took it easy (lead and follow, novice stuff) the first time on track and it acted fine for all 20 min sessions (ambient air temp 50°). 2nd time on track: by session 3 (air temp: 50-70° - AM to PM) when I was beginning to get the hang of track line and increased speed (passed all the Porsches) trans got to 250° and with no DIC codes started up-shifting on its own (about the 15 min point). I got off track and idled to cool it down with trans fan running on high. Next session, same thing. No fun, so went home, took car to dealer, no codes, "Can't help you. Will open an issue with GM." No further word. (Nice, huh?) Changed trans and rear end fluids to eliminate them from equation. Next HDPE, warmer weather but basically the same trans behavior. By session 2 at 15 min point same behavior but at about 275° this time: No codes, or DIC messages, up-shifting on its own, got off track and idled the engine to keep trans cooler fan running until it shut off at about 240°. Car sat for another hour. Back on track, 15 minute mark, same problem. Got back off track. Cooled trans. Went home early. Half way home, check engine light came on. Two minutes later, heard clanking noise from rear. Pulled over. Stuck head under rear. Heard loud rhythmic clanking in "Park" that let me think something was going to fly through the trans case at any moment. Shut it off and had it towed to dealer. After sitting an hour waiting for the tow truck I could start it and drive it onto the flat bed truck and off again at the dealer without noise. Trans temp was at 240° when clanking first heard. It's at the dealer now.

Anyone else with similar issues or solutions like bigger aftermarket coolers/fans that will fit in the same space as original, etc ?

 

[Chip]

CeeSeven; Yours is the first track overheating post I have seen. Are you sure that your tranny cooling fan is running? What sort of ambient air temps. were you running in? From the noise you describe perhaps that sound might be related to the E-Diff rather than the tranny? If the CEL came on, there should be a fault code for your service dept. to check out. Please keep us posted and good luck.

Edit: I double checked my first sentence and did find others with this same complaint.

 

[SwisStingray]

This problem is not new at all.

I have read discussions about the same subject in another forum and this over heating problem with auto gearbox is just cooling (good word for this case ) my willing to choose an A8 for my next Z51 !!!
It's just unacceptable to see a such stupid problem which is still the same in previous Corvette and in this C7 praised as to be a top of the art car...also in the Bowling Green video with Tadge Juechter discussing about the top cooling system.

This problem is absolutely not impossible to solve with simple vents plates, there are possibilities on the rear arms and placed on the crossing part under the gearbox oil cooling fins... But first of all: is there really a cooling fan for the oil transmission ?
I have read that but I doubt it's present, otherwise it is badly placed and have no efficiency. Beside that, placing the exhaust pipes without good heat shields just along the gearbox doesn't help to maintain a decent temp !

Unfortunately along some posts I read, a part of my enthusiasm to own a C7 in January 2015 is just erasing.

 

[Chip]

Yes, the Z-51 has two cooling fans in the back. One for the e-diff & one for the tranny.

 

[SwisStingray]

OK I trust in you, I would like to know where they are.

This over heating problem concerns only the Auto trans, not the M7, so it seems that the cooling was developed for the Manual transmission in head. Perhaps the Corvettes with auto trans are not supposed to be used on the track

 

[Chip]

(From an older thread) Here: http://www.stingrayforums.com/forum/stingray-corvette-discussions/1349-z-51-rear-radiators.html

Here too, talk about the cooling starts @ 5:10 into this video:

 

[SwisStingray]

Thanks Chip, I don't remind this video, I think I have seen another one in which Tadge shown the cooling fins on the underside.

After seeing this part of the video, I'm more in the trouble as the oil radiator for the transmission is not helping to maintain the Auto trans at the right temp. level.
Searching for a reason: it could be because the air which is running in the duct is only used by the radiators, all unnecessary flow is vented directly to the rear side of the car and go outside. If the transmission body is too hot, cooling the oil which is returning to the A6 seems to not be sufficient to cool it as the temps exchange is not big enough to lower the transmission case temp.

CeeSeven is not the only owner who encounters this problem on a Z51...Should be a good thing if other owners over here who have used their A6 on the track with a Z51 could let us know if all was running perfectly.

 

[CeeSeven]

(From an older thread) Here: http://www.stingrayforums.com/forum/stingray-corvette-discussions/1349-z-51-rear-radiators.html

Here too, talk about the cooling starts @ 5:10 into this video

That's exactly what I saw on that assembly line when I picked up my car. Thanks for that video. It's worth 1000 words. The only thing I didn't hear him say was whether the diff cooler also has a fan. I ask because if it exists it was definitely not working on my car: loud fan noise from the tranny cooler on high speed, nothing from the other side. Even though it was the tranny that overheated while not bothering to display a DIC message like other people have gotten 5 min before trans goes into safe mode and upshifts on its own, if it was not cooling well on the diff side it could exacerbate the tranny since they are hooked together physically, but not fluid wise. I'll get a look under there later today or tomorrow while the dealer has it on the lift to see how badly it destroyed itself on track and hopefully see if there is room for a bigger cooler under there. The video, however, shows pitifully little "extra" room there. So the answer may lie in forcing more air with a big honky home made air scoop for track use or something.

 

[SwisStingray]

(From an older thread) Here: http://www.stingrayforums.com/forum/stingray-corvette-discussions/1349-z-51-rear-radiators.html

The only thing I didn't hear him say was whether the diff cooler also has a fan. I ask because if it exists it was definitely not working on my car: loud fan noise from the tranny cooler on high speed, nothing from the other side.

There is NO fan on the right side cooler Seeing carefully the picture shown in the other post show that the oil radiator chassis don't have any possibility to receive a fan like on the other side, so this right side oil cooler probably stays as it is shown on the picture.

 

[CeeSeven]

There is NO fan on the right side cooler Seeing carefully the picture shown in the other post show that the oil radiator chassis don't have any possibility to receive a fan like on the other side, so this right side oil cooler probably stays as it is shown on the picture.

OK, thanks. Just made a contact at GM at the factory and told him [by email] of my (and others') woes. We'll see if I get ignored to death or it goes somewhere.

 

[Chip]

SwisStingray; You may be right about the lack of a fan on the tranny cooler. I have been unable to find proof of its existence, but did find some more on both brake cooling and tranny cooling. (Brake cooling @ 7:50 and tranny cooling @ 8:35) Here:

 

[smajicek]

CeeSeven
Your reported problem is the first I have heard of since joining this forum last October. I would think but I may be wrong that if other forum users that track their cars with A6 and they experienced overheating that they would post it here? I am hoping I am right and you are a rare case that has a problem that needs to be looked at by your dealer. Please keep us posted on your progress/results/resolution

 

[CeeSeven]

CeeSeven
Your reported problem is the first I have heard of since joining this forum last October. I would think but I may be wrong that if other forum users that track their cars with A6 and they experienced overheating that they would post it here? I am hoping I am right and you are a rare case that has a problem that needs to be looked at by your dealer. Please keep us posted on your progress/results/resolution

I started this thread on another forum; there are lots of folks who track their cars, if not all, who know A6's overheat.

 

[SwisStingray]

SwisStingray; You may be right about the lack of a fan on the tranny cooler. I have been unable to find proof of its existence, but did find some more on both brake cooling and tranny cooling. (Brake cooling @ 7:50 and tranny cooling @ 8:35)

For the brakes, that could be fine but for the tranny oil cooling, the fins on the metal lines are just badly situated (at the rear of the tranny and in a "blind" place, facing the rear of the car, without good ventilation) and even if Tadge speaks about a blade to re-direct some air to this piece, it seems that it's efficiency is poor, knowing the too high temperature reached.

I have a long career in the Do It Yourself cooling with my track cars, I think the C7 will be the next one to modify... I know that this sort of mod is quite difficult to achieve with success but nothing is impossible.
Now I don't know if my expectation to choose the A8 will stay alive ! The time to make my choices will arrive certainly sooner than any good test of the Z51 with A8 on the track and that will probably redirect me to the M7 choice...I was expecting a real efficiency of this A8 but having it only on the road is not enough.

The main question now is : Will the A8 be able to suppress those too high temperature problems ? Fitting it in a Z06 could be a successful challenge or a crazy nightmare as more HP = more temperature problems to solve.

 

[SwisStingray]

Copy of one part of a reply in another forum, it does concern the future A8:
"Tadge commented in a session last week at Sebring that they would be doing a lot of engineering to get the cooling on the new A8 in the Z06 to allow it to survive in a track environment. To use his words he called it "Track certified". If they are having to do that much work on a new design with external pumps and valves I'd say this it's quite likely the A6 is not track certified. if it was I wouldn't expect it would need a cool down after 5 laps''

Hope this will also concern the A8 in Z51 !!

 

[slatt C7]

I ran myZ51 auto trans at PBIR in March and had it in manual mode most of the day in 3rd gear most of the time (first time on a track) - no problems.
Then a month later I was at Sebring for the NCM HPDE event and had no problems on the first day. I had trans in automatic mode Sport most of the time - heated up to about 240-250. Then on the second day I played around with the modes more as I was moved to the blue group (they wanted to see how I would handle it if someone was to pass me). I say that so you understand that I was really driving the car - not babying it at all. About the 4th run of the day I put it in Track/Sport2 and the trans did overheat on the 4th or 5th lap (warning bells and DIC message to pull over and stop). And yes the fan was running in the LR trans cooler area.
I pulled into the pit with great apprehension and found the Chevy reps. They called a Trans pro at Chevy. He said it is a known issue and that I should 'let it cool for a while and it would be fine'. I did so and had it back out on the track an hour later. No problem on that run, but I didn't really drive it as hard. I took it to the dealer when I got back home and they said fluid is fine and all is ok. It's been three weeks now and it seems fine, but I do not think this should be happening on a performance sports car that Chevy claims is "track ready" and drive-train is 'covered for 100k miles - even if all are track miles'.
Btw - brake rotor warped mildly also. Dealer turned it and issue resolved.
Car is great but not as durable as I was led to expect.
Also worth noting is that while the performance shift mode is great there is a considerable amount of hesitation when accelerating out of a sharp turn. Well over a second between the time you hit the accelerator and the engine responds. Doesn't sound like much time but it feels like forever when you are on the track and someone is right behind you!

Sent from my iPad using Corvette Stingray Forum

 

[SwisStingray]

They called a Trans pro at Chevy. He said it is a known issue and that I should let it cool for a while and it would be fine.

OK, now we have the official confirmation that the A6 is not to use on the track... or only is used in "tourist mode" driving
It would be, at least, more honest to inform the customers clearly of this "particularity", so they could be able to choose the transmission with full knowledge of the facts.

Some things are very difficult to understand... Sorry for you and the others concerned owners.

 

[urrtoast]

I'm gonna guess the the 8 speed auto will exhibit this issue as well.
Makes sticking with the bullet proof 7-speed that much easier.

 

[mjw930]

I'm gonna guess the the 8 speed auto will exhibit this issue as well.
Makes sticking with the bullet proof 7-speed that much easier.

According to the engineers working the project your guess is probably wrong. The 8 speed is a new design which, if executed correctly should be able to mitigate the heat built up in the clutches. Obviously time will tell but if GM is willing to "track certify" the A8, something they never did with the A6 I would bet the heat issue has been dealt with, at least for the heat generated in HPDE type track events. I doubt it would ever be certified for competition use.


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[rdslon01]

Well, they are planning on using the A8 in the Z06. It had better have resolved the overheating issues...