MarkDFW

I already have a Ron Davis radiator with oil cooler, as well as a tranny cooler. Gauges don't show diff temp so hard to know how hot it runs. I am running with advanced HPDE group and may move to time trials later this year.

How critical is a diff cooler to you guys?

SunnydayDILYSI

Supercharged111

Well one local guy with a C5Z blew up his rear end in TT from overheating. He's since installed trans and diff oil temp gauges on the a pillar. There's another guy with another C5Z and 3.73s, but I don't recall if he blew his up too or just went for some extra torque. It's enough to scare me, but I can only mod as quickly as the funds allow. If you can afford it, I'd definitely do it. All aspects of thermal management are my current top priority, because that prevents the car from breaking which keeps me on the track. It also keeps the car more consistent (i.e. brakes), which allows me to maintain a steady pace and keeps unpleasant surprises to a minimum. When I ran with an alternate group (NASA being primary) last year, they had 30 minute sessions and I managed to overheat my trans toward the end. I imagine my diff was right there with it. I'm curious to see what some of the others have to say who have more experience, but I bet it's a mixed bag of lucky and unlucky folks, the general consensus being get the coolers if you can.

96solo

I've run a few years in TT in Arizona in ambient temperatures of 100 degrees. I've taken temperatures within a minute of a end of 20 minute sessions, and with Redline fluids in trans and rearend the temperatures have never been too hot.

If you intend to run race group, then you will need them.

D.J. Covert
2008 NASA-Az TTS Champion

Supercharged111

I assume your numbers are without coolers 96? What were the numbers?

96solo

Your right about it then. The temperatures ranged from 180-217 degrees with a pyrometer. I never had the temperature light go on, and understand the 270 degrees is the maximum. The Redline ran 20 degrees cooler than the GM fluid.

My rebuilt Corvette has a Dynatech C5R differential now. I will be adding coolers this time around.

MarkDFW

I did have redline put in the diff just recently. Didn't realize it would drop temps that much. Makes me feel better knowing that.

argonaut

I ruined a diff in my C5 running it hard on the track. It got so hot smoke was being drown into the cabin at high speed. Now I have the DRM coolers for diff and tranny. Have had them in for about 35 events now without any issues.

JeremyGSU

This question is going to vary on a lot of things.

1) Driver style
2) HPDE vs racing
3) how long of sessions are you doing, etc.

I have an '04 Z and I've done 11 track days with it and have around 60 total days. I don't have a diff or tranny cooler and I've never even seen the over temp warning. 9 of those days are at Sebring and it gets hot down here. I run Amsoil fluids in both the tranny and diff and change them out every 6 days or so. I run in the advanced group but most of the time I'm probably only running around 80% unless a car comes along that I can battle with.

I also instruct and by the time I get into my car and get out there I'm doing maybe a 20 min session max. I'm also easy on my tranny in comparision to some I've seen. I don't try to shift as fast as I can and shift nice and smooth for longetivity of parts. Some of my friends go out and shift as fast as they can the whole session and are much harder on the cars than I am.

Another thing to consider is what track's are you going to? This will dictate how often you are shifting. Something say like Barber you're going to shift a lot more than at Sebring. Sebring I only used 3rd & 4th and most of the time you're just going along in 4th so the tranny isn't getting used as much.

That's my $.02

However, I would also say if you intend to race I would say you need them. Not sure about DE.

MarkDFW

Once my tires are hot, I'm running about 90%. Sessions are usually 20 to 25 minutes. The two tracks I got to I am in 3rd gear probably 75 - 80% of the time, 2nd in the slow stuff, 4th in the fast stuff. I could go to 2nd more often, but trying not to squeeze the last bit out of the car. If I move to TT, I'd have to push it harder and shift a little more.

I figure changing diff and tranny fluid once a year with the redline I just used will help.

Great feedback. I'd obviously prefer not to spend probably a grand on a cooler, but I suppose that is better than blowing something up. My concern is the diff will run too cool for daily driving. The is with I went with Ron Davis Radiator with oil cooler rather than a dedicated oil cooler. I'm told a dedicated cooler would have the oil too cold for daily driving and not let oil get to optimum temp.

ErnieN85

There is a big difference between C5 & late C6 diff. My C5 Z would have very black fluid when drained after a few track days (that indicates it got hot)
My C6 on the otherhand after many sessions when I drained it last time looked just like new

I'm thinking for DE 20 - 30 min no cooler would be needed
That said if you get a setup with an electrical pump you could switch it on when on track and leave it off for street driving.
for my self I'm going to wait until the diff is worn out.
My C5 Z06 lated 130,000 with no cooler. Then I'll put in a Quafe and a cooler

JeremyGSU

I have a Dewitts radiator and Ron Davis oil cooler (the bigger one) and I do have trouble getting temps up. If it's in the 70's I can cruise on the highway and my oil temp will be in the low 170's and water maybe high 160's-170's. In the cooler weather (40's-50's) the car barely stays above 160's cruising. I have the oil cooler completely taped up with painters temp (next adding saran wrap) and have part of my A/C condensor taped up.

I'm going to reinstall my oem 180 degree thermostat and get rid of my 160.

I've talked to a lot of people about it and while they say it runs on the cooler side most have said as long as it stays above 160 you're OK. If it drops below it then I have a problem.

I would like to see it a tad higher on the street so I'm taping, wrapping, etc. I thought about making some kind of cardboard thing I can tape to the bottom off the car to cut off some of the air flow to the radiator. Something that can easily be attached and removed for when I get to the track.

MarkDFW

This is part of what prompted the question, as I've heard the C6 diff is more durable than the C5, but I don't know how much more it can take. Shop that changed my diff and tranny fluid said both looked pretty good, and that was OEM fluid vs. the redline I had them use. I may have them put in a temp gauge for the diff as a first step and make a decision based on that.

Bill Dearborn

You should go with a diff cooler. GM thought it was important enough that they included a combo tranny and diff cooler in all C6 Z51, C6Zs and C6ZR1s.

Bill

SunnydayDILYSI

Why not just downshift, RPM = Heat

C66 Racing

My SCCA (now T2) setup has a Ron Davis radiator, external oil cooler and tranny cooler, no diff cooler. Been running that setup for what will be my 10th year this year with no ill effects. I change my diff fluid about every 8th track day, which for my schedule and disposable income with my daughters now college age equates to about annually with AMSOIL Severe Gear Extreme Pressure Synthetic 75w90 (Product Code SVGQT).

I have had Phoenix Performance rebuild my diff twice during that 10 years. Once in 05 when I lost the left axle seal and almost all the fluid out of the diff. The diff got so hot it melted the plastic speedometer sensor gear- but won the race! Then again in about 2007 after I hit a wall pretty hard and replaced everything out of caution.

JeremyGSU

The temps I mentioned are highway cruising. If I do drop 5th for awhile as soon as you put it back in 6 it cools back down. If you're cruising for several hours I can't keep downshifting.

C5ZEE06

I've been wondering if keeping the diff fluid temps in check with a cooler translates into better limited slip action for the oe c5Z diff at the track. Anyone know ?

CP Thunder

We ran a practice day at Blackhawk with a brand new Rockland diff with 3.42 gears and melted the speedo gear into the casing. What a mess to clean up. Three sessions about 40 mins each. If in doubt, go with the cooler.

This is what I built for ours. You can do the same thing tucked into the rear quarters..........

VGLNTE1

Nope