swathdiver
Full Access Member
The lift and tires has taken away from your payload on paper. What does the RPO sheet in your glovebox say, GU6 or GU4? Is this a 4x4?
2013 Tahoe/Towing question
- Thread starter iseckora
- Start date
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eh, I'm going to side with the heat makes oils thin, and I'll take jetmans specs for tranny damage as sounds believable. I believe he's done the research. tranny fluid bearly has enough viscosity when new tested at 200deg when new.. test it at 260 and i bet its well blow recommended.
my truck doesn't have a torque converter to heat the tranny fluid, all stock cooling and towing max it will get to is 167. around town hours worth of city driving and you might get 135 to 140deg at the very end. the first half hour of a 80deg day is going to be around 120 ish.
I'm firmly in the you can't really over cool oil or tranny fluid. but that said, I only have my own experience with stuff.
my truck doesn't have a torque converter to heat the tranny fluid, all stock cooling and towing max it will get to is 167. around town hours worth of city driving and you might get 135 to 140deg at the very end. the first half hour of a 80deg day is going to be around 120 ish.
I'm firmly in the you can't really over cool oil or tranny fluid. but that said, I only have my own experience with stuff.
holy 55 page thread lol. wow. I'll have to skim it. seems from the first few pages you've changed everything.
didn't make it far but I did wonder why you worried about 230deg coolent Temps but not 260deg tranny Temps? I've run 260deg coolent temps during track days without a 2nd thought. if my truck hit 230 while towing I don't think I'd even pop the hood?
Like so many other things, I didn't know what I didn't know.
Marky Dissod
Full Access Member
Coolant, Dex3, & Dex6 are at least 3 different things, depending on what kinds of coolants we're talking about.
Although I think today's automotive fluids can WITHSTAND 230F, that doesn't make it cool (sorry).
CAFE MpG standards go ever higher, forcing 'tolerable' operating temps higher to minimize liquid friction coefficients.
Dex6 ATF probably lasts longer between fluid change services @ 221F, than it does @ 248F.
Same applies to motor oil and coolant.
Don't know or care how many MpGs the hotter fluids temps are worth.
Correct.
I copied the data below from the GM P30 chassis guide when the 4L80E was used as a basis for many motorhomes and commercial vehicles. It has since been revised upward but I don't have a copy of anything newer:
OIL TEMPERATURES MEASURED IN THE SUMP
150F -- Minimum operating temperature for continuous operation. It is possible in low ambient temperature to overcool the transmission with oil to air-type coolers; it is hard to overcool if used in conjunction with oil to water coolers installed in most standard automotive radiators.
190F-200F -- Maximum oil level checking temperature. Beyond this, readings are not reliable because of expansion.
285F -- Maximum sump/oil pan temperatures for short duration such as a long hill climb.
300F -- Metal parts inside the transmission begin to warp and distort in varying degrees, seals melt rapidly, and transmission fluid life is extremely short due to oxidation and distress.
AUTOMATIC TRANSMISSION FLUID OXIDATION
Automatic transmission fluid can provide up to 100,000 miles of service before oxidation occurs under normal operating temperatures of about 170F. Above normal operating temperatures, the oxidation rate doubles (useful life of the fluid is cut in half) with each 20 degree increase in temperature. The approximate life expectancy at various temperatures is a follows:
Degrees F Miles
175 100,000
195 50,000
212 25,000
235 12,000
255 6,000
275 3,000
295 1,500
315 750
335 325
375 80
390 40
415 Less than 30 minutes
intheburbs
Full Access Member
@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.
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.
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.
that agrees with everything I've learned watching other race autos. clutches are a soft material, they switched manual transmission synchros to the same kind of stuff, and had to stop using the old school gl5 fluid as it would eat the glue haha so now you put atf in most manuals.
if you got a enough clamping force a clutch pack will hold a lot, but if you let it slip, they don't slip very long before being toast.
tie up he's talking about is the tranny not fully disengaging one gear before engaging the other.. clutches fighting each other.. toast.
it's was always said with the old 700r4 that going into over drive at wot killed them because of just that.. you could throw all the good parts at it, but it would still eat itself alive shifting wise if you let it. had a friend that went thru 8 of them in a 12sec car. it was brutal, 4.10 gear needed 4th before the traps.
I also very much agree that sump temp doesn't tell the full story. tranny and oil temp in the system is higher than what we are seeing on the gauge in different spots, that's where the high temp spec of synthetics come in handy. another reason I don't believe in over cooling damaging things like everyone says.. fluid inside a slipping converter at take off will get well passed the condensation point even at cooler pan temp. same with engine oil, you're pan might be cooler, but that oil flowing over your exhaust valves, springs and the head overall will be hotter, along with what's splashed under the piston. I've seen corvette guys remove factory old coolers because oil Temps don't get to 200deg for them, but at the same time their coolent Temps run 210-220 stock. if the water in your head is 210 the old flowing over it is atleast that. that's enough along with the pvc system to remove condensation.
good to see gm testing to 200k that's nice to hear. I hear lots about the new 8 and 10 speeds crashing and burning like clookwork at 100k. probably no maintance then if they are targeting 200k in the lap.
Marky Dissod
Full Access Member
In the context of
www.tahoeyukonforum.com
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.
2013 Tahoe/Towing question
Afternoon all!! I have a 2013 Tahoe with a 3.5 inch rough country lift, and a 3 inch body lift, riding on 33s. My question is I am a travel contract worker and my gf is as well. We are looking at taking a contract in Alaska for a bit and we want to take her 2016 Jeep Wrangler 4d. Is my tahoe...
www.tahoeyukonforum.com
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.
Last edited:
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