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Automatic C7 Trans Overheating on track

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Old 05-20-2014, 09:43 AM   #41
NSC5
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Hopefully the "new" version of GM will be more responsive and willing to address overheating concerns but since only a very small percentage of owners are going to drive the A6 equipped C7 hard enough to create the concern I wouldn't hold my breath. If the A8 better manages temperature on the track I expect it will be even more difficult to get A6 issues addressed since from GM's point of view the problem won't be getting any bigger (since the A6 production run will have stopped).

A lot of guys jumped through a lot of hoops with GM starting back in 2004 when the new LLY revision of their diesel was introduced to meet new EPA standards and people quickly started experiencing severe overheating issues with both the engine and transmission when towing well within the rated specifications. The only real solutions were after-market and GM didn't solve the problem until the introduction of the LBZ third generation diesel with revised cooling for both the engine and transmission. I am very happy I skipped from the first to third generation and avoided the frustration.

If you need to kill some quality time in front of your PC here is a thread that links to the various twists and turns owners went through. I think the lesson learned from this is an aftermarket solution may well be the least frustrating and best solution. Hopefully those aftermarket products appear soon for the guys tracking their A6 equipped Stingrays. http://www.dieselplace.com/forum/63-...-problems.html
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Old 05-20-2014, 11:42 AM   #42
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Got the car back and did a first effort mod on the air intake for the trans and diff. Here's the trans air scoop before sealing up the air leak at the inside rear. 1st opportunity to test it is next Sat and not a good one with a small track (.75 mile) at CAC and short lap count. Better test at Inde a week from Sat.


Did you ever test your duct scoops on the track? Those things look like they will really increase the air flow through the cooler. I'd have to believe that would make a significant difference in the trans temps. My only concern would be that the fan may not be able to keep up with that amount of flow but that shouldn't hurt anything.

Last edited by slief; 05-20-2014 at 11:45 AM.
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Old 05-25-2014, 01:10 PM   #43
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Let me see if I have the gist of this thread, A6 C7's even with the Z51 package over heat when tracked?

I thought that's what the Z51 was designed for.
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Old 05-25-2014, 05:49 PM   #44
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Let me see if I have the gist of this thread, A6 C7's even with the Z51 package over heat when tracked?

I thought that's what the Z51 was designed for.
Most autos for most performance cars have heat issues at the track. The Z51 improvements are not enough, it seems. MT or DCT for the track it looks like,
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Old 05-25-2014, 06:01 PM   #45
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Most autos for most performance cars have heat issues at the track. The Z51 improvements are not enough, it seems. MT or DCT for the track it looks like,
Thanks for the info, my track days are over hence my order for the automatic, but I thought the Z51 had extra coolers for track duty.

All my previous Vette's have been manual's so I really never paid much attention to this.

Live and learn.
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Old 05-26-2014, 01:38 AM   #46
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If you are trying to increase air flow to the coolers mounted in the rear of the car pull the grating out of the quarter panel inlet vents. When I was at Carlisle last August I spent a fair amount of time talking to the engineer that designed them. He spent a lot of time minimizing the air flow restriction caused by the grating. When I asked him how much they restricted the air flow he said about 25%. When I asked if the gratings could be removed he said yes but then you have to worry about items falling into the cooling ducts.

The cheap thing to try is to remove the grates and see if enhanced air flow through the coolers will help. I don't know whether that will help cooling an automatic since I don't think the auto trans cooling circuit uses those coolers.

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Old 05-26-2014, 10:08 AM   #47
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If you are trying to increase air flow to the coolers mounted in the rear of the car pull the grating out of the quarter panel inlet vents. When I was at Carlisle last August I spent a fair amount of time talking to the engineer that designed them. He spent a lot of time minimizing the air flow restriction caused by the grating. When I asked him how much they restricted the air flow he said about 25%. When I asked if the gratings could be removed he said yes but then you have to worry about items falling into the cooling ducts.

The cheap thing to try is to remove the grates and see if enhanced air flow through the coolers will help. I don't know whether that will help cooling an automatic since I don't think the auto trans cooling circuit uses those coolers.

Bill
I don't know what the flow is in that region. I don't know if there is sufficient area for a NACA cell on the stock fender. What they have on the C7 and C7 Z06 doesnt look very efficient to me. I doubt that it would be much difffernt to the C6R flow but at least the C6R had space for a decent NACA cell. The C7R doesnt have an inlet here.
I wouldn't place a scoop or periscope intake there like some have done because of drag and effectiveness and airflow disruption to the spoiler. Since the C7 Z07 package has adjustable aero bits, maybe they can offer a removable screened lid on this intake for race day.





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Old 05-26-2014, 11:50 AM   #48
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I wonder if the new A8 will have extra cooling "tricks" that can be retro fitted to the A6?
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Old 05-26-2014, 01:01 PM   #49
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Thanks for the info, my track days are over hence my order for the automatic, but I thought the Z51 had extra coolers for track duty.

All my previous Vette's have been manual's so I really never paid much attention to this.

Live and learn.
The Z51 has the same auto trans cooling as the non-z51. Appears to use the same engine oil cooler as well, but the Z51 has dry sump which should run cooler.

The manual trans Z51 has a cooler where the auto cooler is, non-z51 has no manual trans cooler.

Z51 option also has a differential cooler on the RH side.
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Old 05-26-2014, 01:09 PM   #50
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The Z51 has the same auto trans cooling as the non-z51. Appears to use the same engine oil cooler as well, but the Z51 has dry sump which should run cooler.

The manual trans Z51 has a cooler where the auto cooler is, non-z51 has no manual trans cooler.

Z51 option also has a differential cooler on the RH side.
I guess my question wasn't very clear, my question was about the Z51 having "extra coolers" for the A6 since that what this thread is about. So in essence the Z51 A6 is not a good track car.
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Old 05-26-2014, 01:32 PM   #51
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I guess my question wasn't very clear, my question was about the Z51 having "extra coolers" for the A6 since that what this thread is about. So in essence the Z51 A6 is not a good track car.
Nothing is different for the auto trans cooling between the Z51 and non-z51. GM consolidating parts most likely.

It certainly isnt a good track car for people that have tried and went into limp/trans overheat mode

But it may work for others, IMO if you seriously tracking a C7 the manual would be the way to go. Going to have to wait and see if the '15 A8 brings any cooling improvements.
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Old 05-26-2014, 03:52 PM   #52
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Default Results at Inde

With the air scoops on at Inde (http://www.indemotorsports.com/site/...ction_thetrack) this weekend it lowered trans temps about 10 at the same ambient temps as in March when the problem was 1st noticed, same track (config 1CW), same track config, same lap times. When the track config was changed (2CW) on Sunday to add 3 demanding corners the temps got hotter, quicker than back in March with the same up-shifting on its own as before. Still no DIC messages and no codes.

Conclusion: No size air scoop other than something huge is going to fix the problem. It needs a second trans cooler (up in front?) since there is no room back there for a bigger one - or to correct the bad angle of the existing cooler that reduces air flow because of angular air flow.
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Old 05-26-2014, 06:51 PM   #53
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With the air scoops on at Inde (http://www.indemotorsports.com/site/...ction_thetrack) this weekend it lowered trans temps about 10 at the same ambient temps as in March when the problem was 1st noticed, same track (config 1CW), same track config, same lap times. When the track config was changed (2CW) on Sunday to add 3 demanding corners the temps got hotter, quicker than back in March with the same up-shifting on its own as before. Still no DIC messages and no codes.

Conclusion: No size air scoop other than something huge is going to fix the problem. It needs a second trans cooler (up in front?) since there is no room back there for a bigger one - or to correct the bad angle of the existing cooler that reduces air flow because of angular air flow.
After crawling around under my Z51 A6, I was thinking the same thing. It doesn't look to me like the A8 cooler is nearly big enough to solve this problem either. I think re-routing the ATF cooler lines to in front of the engine radiator and doubling or tripling the cooler heat exchanger core size may be the only solution. The increased line length may be an issue, but could also help in that it will provide more length to convectively cool the ATF.

Alternatively you could look into those massive ATF coolers they use on the big 2500 and 3500 series trucks - should provide some additional heat capacity, but finding the volume with the right airflow could be a problem. See: http://www.transmissioncoolers.us/ca...oolers-hd.html Where there is a will there is a way, but if you really want to track your C7 ALL DAY, the M7 may still be your best option.

Last edited by dcbingaman; 05-26-2014 at 07:01 PM. Reason: Update
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Old 06-21-2014, 10:28 PM   #54
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Snoreman, You monitoring this thread still? If so check your personal messages for an update on the A6 overheating issue. Everyone else will have to wait another 2-3 weeks or so for the resolution.
In the meantime, I can tell you that sources that I cannot reveal tell me that the 2015 A8 will likely have the same overheating issues as the A6 - especially on the ZO6. So if you track buy an M7.
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Old 06-21-2014, 10:40 PM   #55
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My A6 Z51 Vert runs at +220 after 1 hour of just plain old driving. It is a bit disconcerting.
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Old 06-22-2014, 10:12 AM   #56
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My A6 Z51 Vert runs at +220 after 1 hour of just plain old driving. It is a bit disconcerting.
I think when I get my Z06 I will try to avoid looking at the transmission temp if your Z51 is running this hot under cruise conditions. 220F at the converter output wouldn't be bad but I am sure this is a sump temperature reading. Maybe GM has decided that it is OK to run them this hot but it isn't rocket science to calculate the heat load of an automatic and put a cooler where it receives sufficient air flow to achieve a lower temperature. Saving the few pounds that a large stacked plate cooler with lines to mount it where it receives airflow isn't much of a gain when this weight savings results in a car that limps quickly when pushed.

They certainly manage to cool transmissions properly in other applications. The highest I have ever seen in my 2006 GMC pickup was just barely past the 200 mark towing a little over 10,000 pounds up to the Eisenhower tunnel in the summer running at the speed limit. Normal highway cruising is 160-170 during the summer months, goes up to 180 in heavy stop and go summer traffic and drops quickly back to 170 when the fan clutch engages.
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Old 06-23-2014, 11:11 PM   #57
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I've said it before, and I'll say it again...I seriously doubt GM is going to be able to control temps for the A8 in the Z06.
We've seen pictures of the Z06 cooler compared to the Z51 (I actually started a thread in that section), and it's only ~30% larger. They can lock the convertor and decrease some fluid temps, but considering the current A6 is already not capable of anything more than ~10-12 minutes on-track, I take GM's BS "track certified" comment with a grain of salt.
"Track certified" for whom? A novice driver on an easy track in ~50-60* ambient temps?
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Old 06-23-2014, 11:48 PM   #58
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Maybe GM has decided that it is OK to run them this hot but it isn't rocket science to calculate the heat load of an automatic and put a cooler where it receives sufficient air flow to achieve a lower temperature. Saving the few pounds that a large stacked plate cooler with lines to mount it where it receives airflow isn't much of a gain when this weight savings results in a car that limps quickly when pushed.

They certainly manage to cool transmissions properly in other applications. The highest I have ever seen in my 2006 GMC pickup was just barely past the 200 mark towing a little over 10,000 pounds up to the Eisenhower tunnel in the summer running at the speed limit. Normal highway cruising is 160-170 during the summer months, goes up to 180 in heavy stop and go summer traffic and drops quickly back to 170 when the fan clutch engages.
I second that motion that this is just basic mechanical engineering. It is hard to believe that designers don't seem to connect with engineers and then send it to R&D for testing. This has been going on for at least 35 years at GM. My brother, a mechanical engineer, worked for GM in future forecasting [of systems design for cars to hit the market in 8-10 years] in the '70's. He got so frustrated by having his [and his fellow engineer's] reports and analysis flatly ignored and seeing defective designs go in to production [because it was cheaper] that had to be fixed by dealers or just pissed off customers by having NO answers that he and a bunch of his buddies quit GM and went out and formed their own consulting firm farming out their expertise to the Japanese. They listened and made good cars !!!

There is plenty of unused room in the C7 engine compartment for one or even two additional coolers and two blocked off grill sections to feed it/them with air - exit air through side vents. Things I do not know is where to run the lines from the back. Space is at a premium -- and I don't know if the current pump would suffice. Maybe someone else more knowledgeable than I would know about those aspects.????
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Old 07-07-2014, 12:26 AM   #59
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Has anyone had at least some improvement with a different transmission fluid? If it overheats should you change it? Will a fully synthetic hold up under these conditions?
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Old 07-07-2014, 01:45 PM   #60
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Has anyone had at least some improvement with a different transmission fluid? If it overheats should you change it? Will a fully synthetic hold up under these conditions?
I spoke to an engineer at Red Line a couple of months ago. He said he recommended their DF4 rather than DF6 (which is a direct replacement for Dexron 6). DF4 has less slipperiness agent in it, so it will slip less (slightly less silky shifts) and will run cooler. Amsoil said the same thing only with their ATF.

Having said that, we are almost certainly NOT talking about a 30 difference as a result of changing fluid brand/types, which is what is needed in the A6 and the coming A8. And, more importantly, we never really have established what a sustained fluid temperature would be under sustained track runs since I don't know anyone who has made it past the 15 minute point. At that point, when the trans goes into limp mode and up-shifts on its own the fluid temp is still rapidly rising past 250-260, etc.
Bottom line: not enough cooling designed into the car.
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