2013 Tahoe/Towing question

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Geotrash

Dave
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wouldn't this fully support that running 265deg tranny Temps while towing is a horrible idea if you can add a cooler to keep it 220 or less?
That’s exactly what I’m doing and advocating. But it’s also perfectly acceptable to see a peak of 235°F or even more for a short time at the top of a pass. And that it’s important to set 150°F as a minimum fluid temperature year round. So that’s what I’ve set up on my 2012.

Also note that the chart is fluid life, not transmission life. And that’s with older fluids.
 

Geotrash

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@Geotrash

4L80- so that's Dex3.
Dex6 can handle much more.

I have a friend who worked at GM. Wanna guess his job? Transmission validation engineer. Wanna guess his first project when he was hired? 6?80/6L90.
I picked his brain...here's our chat...money shot at the end, highlighted in red

PM discussion with a former GM transmission validation engineer, who was part of the validation team for 6L80/90, now working at Tremec:

Me: The old 4-speeds in GMT800 were nice in that third gear was 1:1 ratio. Easy-peasy, tow in third, the trans is a pass-through. What to do with 6L90 with no 1:1? I know with the 4Ls, OD/fourth was using the small planetaries, and you don't want them working that hard. Are both ODs in 6L90s using planetaries, or 5th not so much? Bottom line question - tow in 4th or 5th with 6L90?

Transmission guru: I'd probably put it in tow/haul mode and let it go that way. The anti shift busyness cals should keep the trans from hunting gears too much. How does the rear end ratio compare to your 4sp truck? In terms of power flow the 4-5-6 clutch locks the input shaft to the planet carrier for the rear gearset. 4th uses the front gearset to drive the rear half of the rear gearset while 5th drives the front half. The 1-2-3-4 clutch does have more capacity than 3-5-R but that's more of a shifting thing than during cruising. I did some dyno tests for the 6L80/90 and our dyno rig simulated GCVW and ran through all the gears. 4th is tested to more overall gear damage, but that's true of any lower gear. I'd be more concerned about the clutch adapts and if there are any shift flares or tie-ups. That sort of thing will hurt the trans more than anything else.

M: And to interpret some of what you typed, you're saying you saw more gear damage in 4th, or just that it was tested more?

T: Tested to a higher level of damage. Damage targets are based on simulation data and lower gears get more damage generally because more time at high throttle is spent in the lower gears vs higher gears seeing more cruising time. Wondering how high the rpms would be on the highway in 4th. The shift map may end up never hitting 6th with the additional load from a trailer anyways

M: Ok, so the takeaway is that I should be more concerned about running in a particular gear to minimize shifting/hunting, vs a blanket statement that "this gear is bad to tow in because it puts additional strain/stress on the transmission."

And I seem to recall it'll still kick down to 4th when I floor it at 80, so 6k RPM in 4th is probably near 100 mph.

T: High rpm sustained is going to heat the oil in both trans and engine.

M: Yes, I've experienced that. Did a long pull towards the Eisenhower Tunnel - 40 MPH, 2nd gear, 4k RPM, trans maxed at 243°, 16,000 lbs. So looking at the ratios, 4th is just about exactly double 2nd gear. So if 2nd at 4K RPM gets me 40mph, then 4k in 4th is about 80, and theoretically almost 120 mph at redline in 4th.

T: Yeah, that's about 120c. Toasty. I'd add cooling capacity if you do that frequently. 120c is the hottest you want to sustain, but not forever. 140c would be an immediate shutdown, but the TCU may start requesting torque cuts or giving you a warning before then.

M: The only times I've gone that hot were when I was crossing the Continental Divide in either Wyoming or Colorado. I seem to recall, whether it was you or someone else, that the "trans hot, idle engine" comes on at 262° or 265°.

T: Probably someone else, but that's definitely hot. It's also the sump temp. Torque converter temps are higher and clutches can be also if it's shifting a bunch. Fun thing, clutches in an automatic are essentially paper with fancy glue.

M: So, to circle back around, my main goal to maximize longevity and minimize stresses on the trans, is primarily to minimize shifting, and not worry about staying out of a particular gear?

T: Just don't slip them that's what the torque converter is for. Yeah, I'd worry more about excessive shifting. Shifts aren't really bad as long as they are smooth and it's not hunting. If there is a slip or tie up that's ******* clutches and parts. The gears are all strong. 6th has an output rpm limitation because of the power flow, but that's a CTS-V issue and the cal will drop onto 5th at something like 120.
The 6 speeds were definitely tested with a 200k life working hard the whole time.
I agree with all of this, thanks for sharing! I posted the excerpt to establish that what I advocate for running for fluid temps would have been perfectly acceptable with earlier transmissions and Dino (dex3) fluids also.
 
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intheburbs

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wouldn't this fully support that running 265deg tranny Temps while towing is a horrible idea if you can add a cooler to keep it 220 or less?

i would never run 100k miles without a fluid change or 3 if worked hard. I sent off a tranny fluid sample with like 7k miles on it after a 2k mile tow and even thou it came back good after jetmans post sent me down a fluid rabbit hole, I'm still considering changing the acdelco I put in it to amsoil, if I can get over the 200+$ price tag before my next tow haha. but a tranny is way more expensive. I like rebuilding manual trannys, I don't even like that though of touching an auto.

In the context of
and

Pretty sure the following chart is old enough to apply to Dex3 but NOT necessarily to Dex6:
176°F / 80°C . . . 100,000 Miles ... Ideal temp
194°F / 90°C . . . 50,000 Miles ... Maximum recommended sustained temp
212°F / 100°C ... 25,000 Miles ... Pressure drops
GM seems to be looking for MpGs in between 212°F / 100°C, & 230°F / 110°C
230°F / 110°C ... 12,500 Miles ... Varnishes Form
248°F / 120°C ... 6,250 Miles ... Seals Harden
275°F / 135°C ... 3,125 Miles ... Clutches Slip
293°F / 145°C ... 1,562 Miles ... Oil forms carbon, seals and clutches burn

Over 293°F / 145°C, measure in minutes instead of miles.
To quote the communique between 'intheburbs' & a former GM 6L80E / 6L90E Validation Engineer

...
T: High RpM sustained is going to heat the oil in both trans and engine.

M: Yes, I've experienced that.
Did a long pull towards the Eisenhower Tunnel - 40 MpH, 2nd gear, 4k RpM, trans maxed at
243°F (117.25°C), 16,000 lbs.

T: Yeah, that's about
120°C (248°F). Toasty.
I'd add cooling capacity if you do that frequently.

120°C (248°F) is the hottest you want to sustain, but not forever.

140°C (266°F) would be an immediate shutdown
but the TCU may start requesting torque cuts or giving you a warning before then.

M: The only times I've gone that hot were when I was crossing the Continental Divide in either Wyoming or Colorado.
I seem to recall, whether it was you or someone else, that "trans hot, idle engine" comes on at 262°F or 265°F.

T: Probably someone else, but that's definitely hot. It's also the sump temp.
Torque converter temps are higher and clutches can be also if it's shifting a bunch.
Fun thing, clutches in an automatic are essentially paper with fancy glue ..."

Based on what the transmission guru dun told you
"120°C (248°F). Toasty. I'd add cooling capacity if you do that frequently."
"120°C (248°F) is the hottest you want to sustain, but not forever"
"It's also the sump temp. Torque converter temps are higher and clutches can be also if it's shifting a bunch."
"clutches in an automatic are essentially paper with fancy glue"

110°C / 230°F is more than hot enough for motor oil, ATF, and antifreeze.
Not quite sure what your point is with that post.

But I can address your "chart..."

No, it doesn't apply to Dex6 nor the 6L80/90.

- They were designed for operating temps of 190-200°
- Yes, my friend recommended extra cooling capacity if I was getting that hot on a regular basis. I don't. And as has been previously addressed, keeping the trans perennially below 150° because you have to much tooling capacity is worse than a few brief excursions into the 240s.
- Seals don't harden at 248°. Nor 300°. Nor 350°. Seals used in transmissions are made of fluorocarbon rubber (most common tradename is Viton). Viton is rated for operating temperatures to 400°. How do I know this? I sell seals for a living. And many of our customers include ZF, Tremec, etc.
- I've owned my Suburban for 10 years, and in that time I've put 135k on it. And I've done a full trans flush 5 times. 16 quarts.
- You seem to keep mentioning coolant. Transmission fluid is not a coolant. It's a hydraulic fluid designed to transfer mechanical energy and lubricate parts. It gets hot doing that, so the fluid is routed through a heat exchanger to lower the fluid temperature.

I think we've beaten this to death enough. I'll keep doing what I'm doing, you do you.
 

petethepug

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Why not just call around to a few shops you’ll be near in AK an see what they recommend. Take the best of the info you get from the horse’s mouth.
 
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Assuming OP's Tahoe has the factory trans cooler, a larger one is unnecessary IMHO. 190-200° F is normal operating range for the 6L transmissions. Dex6 has substantially better high-temperature capabilities than Dex3. And low temps can be just as bad, or even worse, than high temps. If you're not getting above ~150°, you're not boiling off condensation that may have collected in the transmission. And we all (should) know that water in the fluid is bad.

I just have the small factory cooler in my Suburban. 240k miles, still original, still operates perfectly. And I beat the crap out if it. If I'm just driving, I'm cruising down the highway and high speeds (90-100+), or I'm towing either my 4,000-lb cargo trailer or 8600-lb travel trailer.

My personal record is 243°, usually achieved when I'm going over the Continental Divide with the travel trailer. I simply change the trans fluid more frequently. Sometimes with an interval as low as 30k miles. But usually I do it every 50k. Full flush - at the dealership. 16 quarts.

This was on I-70 eastbound towards the Eisenhower Tunnel, 7% grades, pulling the behemoth right at 16,000 lbs gross vehicle weight...

Had two thoughts reading this

I love watching the towing torture test videos pulling the Ike- My favorite is the Rivian electric truck w/8000lb behind that had to stop and recharge before it even got there from Boulder

And, Thanks for putting my mind at ease. I worried for years about the 209* temp(my personal record) mine reached on I-64 coming up out of the New River Gorge each of the handful of times I tugged too much weight to the Greenbrier Resort and back. Far right truckers lane, pedal to the floor, M5 selected on the shifter, tow/haul engaged, and hanging on by a thread to 50mph the whole climb......and pucker factor was about 8.75 of 10
 

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