blackbeast99

Running a few DE's a year, and even in this cooler "fall" weather, during long sessions I get "Transmission Hot - Idle Engine" after a solid 20 minutes of running . 2008 Z with stock tranny...what fluid are you guys running or did you upgrade the cooler?

I also notice that occasionally when I reach 145-150mph, my speedo stops working, falls to 0mph and doesn't come back until I downshift. Speedo sensor or related to the tranny heat also?

brkntrxn

I run Mobil 1 fluids in my engine, trans, and diff. Sounds like you need to upgrade your trans cooler or put one on your diff.

Speedo - Mine acted similarly after running an enduro a couple years ago. The speed sensor in the diff is going bad. Easy to get from GM and a 10 minute swap.

blackbeast99

Thank you for the input...that's what I've been thinking. I've been looking around at a few different options to upgrade the tranny cooler or add one to the diff.

kmagvette

I have been running Red Line D4 in my transmission for the past 9 years...same transmission. I do about 15 days/year at Watkins Glen for really close to 25K track miles. Transmission is still strong. I should have installed cooling on it and the differential but have not; I get dumbA$$ credit for that. With the D4, it takes about 20 minutes on a hot day to get the tranny temp warning. Fluid is always clean at the 1x/yr fluid change.

I suspect I would have had similar experience had I used other quality fluids such as Mobil1, Amsoil, etc.

C66 Racing

I use this in my 02 Z06 at the track:
AMSOIL Torque-Drive Synthetic Automatic Transmission Fluid (Product Code ATD1G)

I thought the 08 Z06 had a tranny cooler on it, no? I'm surprised to see you getting a tranny temp warning.

My 02 Z06 didn't come with a cooler and I got the warning at my first DE in the car way back when. Cooler came very shortly thereafter and haven't had a high temp warning in 10+ years of racing or track days.

On my 02 Z06, the speed sensor comes from the diff. I know because I melted it in 2004 when I lost my diff left axle seal and half the diff fluid. Won the race, but melted most everything attached to the diff. In that case, my speed went away with about five laps to go and it never came back (and I took the diff out and had it rebuilt).

But again, I thought the 08 Z had a diff cooler as well. I now have a diff cooler on mine.

parsonsj

It does. All C6 Z06s have transmission coolers, but it's very common to get that warning after about 20 minutes. The faster you go, the more likely you'll see that warning. The Z06 uses a thermal transfer block so the transmission fluid also cools the differential fluid. Word is that the real culprit is the diff. There are a couple solutions out there (DRM, LG), including mine:

https://www.corvetteforum.com/forums...oler-idea.html

C66 Racing

Thanks for the clarification. Didn't know, or forgot, the tranny cooled the diff. And based on my experiences at the track in my C5 Z06 which drove me to add a diff cooler, suspect you are correct. With my stand alone and separate tranny and diff coolers, I haven't gotten a tranny high temp since I installed my tranny cooler.

stevensa

I use the same fluid purchased through the same person

LateBreak

I put GM Synchromesh in the one that I just had apart, it's what Tremec recommends and probably factory fill on your 08. I'd focus more on controlling the heat than using a different fluid, try wrapping the exhaust where it runs near the trans and it wouldn't hurt to upgrade the cooler. Thankfully since you have a factory cooler pump, that's a fairly easy upgrade to the cooler itself I'm sure Randy@DRM has some good options available.