Automatic C7 Trans Overheating on track
 

C7, Z-51, mag shocks, performance exhaust.
A post on this subject is elsewhere, but not in the tech section.. So I brought it up here where we can find it.

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?

Honestly, IMO, the auto trans cooler location on the C7 isnt that great. Its 'cool' and all but an auto trans makes a lot of heat when beating on it and by the size of that cooler and the intake/exit ducting an oil/water heat exchanger in the radiator with an add-on cooler in front is a better setup. A couple magazines testing the C7 A6 on a road course mentioned going into protection mode after a short while.

Mine gets fairly just playing around on mountain roads,and there is a huge difference between that and a real road course.

Solution? Watch what the new auto Z06 does for a cooler, and copy it when the parts come out, my guess is there will be some changes from the regular C7 auto cooler.

You are not alone on the trans overheating on the track. Below is a thread on this subject. Not sure what the fix is. It's possible that the Z06 fan may work on the Stingray but since the Z isn't out yet, it will be a while before that can be tested. The Z06 also appears to have a larger cooler but also has larger rear ducts so I'm not sure if a cooler upgrade will be possible on the Stingray either. Since this seems to be a universal issue when tracking the A6 C7, I suspect somebody will either produce a larger trans cooler or cooler fan retrofit kit at some point.
Another potential fix may be to swap in the Z06 upper fender intake grills onto the Stingray as they have a little scoop on the top to force more air through the ducting. I think there is a vendor with a similar solution already. I will look for that thread.

http://forums.corvetteforum.com/c7-g...this-week.html

Here is a picture of the cooler duct inlet on the Z06. Notice the little scoop.. That will force more air in through the cooler. This would be the first route I would go if this part were available. As I said above, I think there is already a vendor doing something similar. I just need to find the thread.
http://i390.photobucket.com/albums/o...ps13968e4c.jpg

Here is the quarter vent I remember seeing for the Stingray. Not sure how much more air it will force through the coolers as it really doesn't look like it sticks up as much as the Z06 version but this may help a bit. If you could get them unpainted, you could heat the scoop part up and bend it upward a bit (if it's plastic) to capture more air. These appear to snap onto the existing vents so install should be a snap (literally).
http://i390.photobucket.com/albums/o...psd201b7fb.jpg

Source:
http://www.corvettemods.com/C7-Corve...c_p_10138.html


Edit: These appear to be stainless but I'm sure you or a body shop could easily tweak the lip on it up so that it functions more as a scoop to help direct more air into the coolers.
http://www.corvettemods.com/C7-Corve...c_p_10136.html

Auto transmissions overheating at the track has been a problem on many cars for years. Autos just don't cope well with the stress of track driving. The auto in my C63 did the same thing... so I sold it. I've driven two other autos at the track and both have had issues. I have never had an issue with a MT or DCT.

If you want to track the car, you will probably need after market cooling options or get a 7MT. I would have thought GM would have addressed this but it appears not... I suspect the number of C7s at the track that are autos are a relatively small number (many owners won't track and many that do will have a 7MT) so GM was probably not all that motivated to spend a lot of R&D to fix an issue that would likely impact a relatively small few. Still the wrong answer but my guess is this is the case.

Thanks for all the input guys.

I intend to have a look at the car after they get it up on the lift and expose the coolers Monday. I want to see if there is any room for a bigger one - or two. Isn't there one for the rear end on the right side too? I noticed that I didn't hear any fan noise from that side. Isn't that one supposed to have a fan too? If there is supposed to be another fan it isn't working.

I'm not opposed to going to a [fiberglass] fabricator and getting him to make me a big honky air scoop that sticks way up that will grab a bodacious gulp of air at speed that will attach and detach easily for track use.

A question for anyone. Is there a typical damage to the trans that might occur from overheating that is the culprit for the loud clanking I heard that made me stop and tow it away, and how much of a fix is it?

To expose the coolers you will need to remove the rear fascia/bumper on the car. I wouldn't expect the dealer to do that unless there is good reason or unless you pay them to do so. Any of the things you mentioned would not require the rear fascia to be removed.

I have the convertible, and it doesn't have the inlet scoops. So it would not be a track car. fluid temperature runs 220+ after 3 hours of highway driving. These 2 photos are of the "cooler" on a conv. There are 2 of these finned coils in back of diff.
http://forums.corvetteforum.com/memb...735-171617.jpg
http://forums.corvetteforum.com/memb...717-171616.jpg

I hope it runs the transmission fluid through a cooler loop in the radiator. The size and placement of those can't provide a lot of cooling.

Oh, can't get to them from the bottom, huh? Do you know if there is supposed to be a fan on the right cooler - the differential cooler?

And Kenrobb: thanks for the pics. Your rag-top is much different. Mine runs about that temp on highway too.

Those look like some heat sinks on the e-diff cooler lines, as far as I know the verts use the same coolers as the coupes, they just pull the air from under the car instead of the upper ducts like the coupes.

If thats an actual diff or trans cooler I've seen larger power steering coolers :)

Those are not the coolers used in my Z-51 coupe. I saw Z-51's being built on the assembly line and the coolers for the tranny is on the driver's side at the rear quarter panel just inside the rear fascia/bumper right in front of the vertical vent in the bumper. Z-51 coolers (or at least the tranny one) are rectangular, about a foot long and 8 inches wide and maybe 2" thick (like a mini radiator) with a fan right in front of at least the tranny cooler and is ducted air from the horizontal vent on the fender sort of above the gas cap door. That was the one I could see from the walkway on the assembly line. It was hanging down before the fenders, bumpers, etc went on and it got hooked up. I'm hoping to get a first hand look under there on the lift later today or tomorrow while the dealer is finding out how bad it is inside the tranny so I can see how much room there is under there in case there is enough for a bigger aftermarket cooler - and to see if the diff cooler has a fan since I did not hear it running when the tranny fan was on high. Will update after that.

Differential cooler does not have a fan.

There are some pictures Snoreman posted a while back of the larger Z06 auto trans cooler and fans if you search around.

10-4. Thanks for the info.

Found it:

http://forums.corvetteforum.com/c7-z...n-coolers.html

Z06 trans cooler pics.

You will need a really big cooler with lots of airflow. More oil capacity would help. Not worth the trouble in the end. I do not believe the z06 auto will work well on warm track days either.

If it doesn't, Chevy will (rightfully) take a lot of heat (pun!) over it. "Most track capable" yada yada yada... I hope you are wrong...time will tell.

They were referring to the manual :D

Thanks kp. Interesting, even though these pics are development versions, obviously, not the production ready version. Too early for that. The core IS bigger. That's about the size the base Z-51 needs. Wonder if it will fit in mine??

I just made contact with a GM rep at the factory yesterday and told him of my [and others'] woes. We'll see where that goes. No word on my broken car at the dealer yet.