6L80 Heat Related Symptoms

[CTX-SLPR]

Howdy,

Well now the weather is warming back up, I'm getting the same symptoms as I was before I fixed the missing check ball in my 6L80. Watching the temp in the DIC (scan tool showed within a degree last we checked) and it's hitting over 200ºF in 55mph surface streets with lights. Once it gets over 195º it starts to feel like the vehicle stops faster than the trans can downshift so it surges just before coming to a stop. It also has very lightly lurched into gear from a stop at over 200º.
I think the main culprit is something in this unknown reman transmission is binding up when it gets hot so if I can keep it cool it works fine but considering @NickTransmissions statements on DEX6, this should be well within operating range. I put a Zipkit (minus the pump bits) in after consulting with Sonnax already so I'm wondering if it's transmission hardparts or control complex related. I'm going to put a 40K on it before summer but that's definitely only a bandaid to keep it out of this territory. I might feel fine selling it like this but not towing with it.

Insights or Thoughts?

 

[Charlie207]

How long does it take to get the AT up to 200F?

Do you have a factory cooler, or any cooler installed?

 

[CTX-SLPR]

How long does it take to get the AT up to 200F?

Do you have a factory cooler, or any cooler installed?

I was up to 200º within 45min of around town driving at ~85-90º ambient. I only have the factory radiator tank liquid to liquid cooler. The plan is to swap to OEM lines and a Tru-Cool 40K at some point but like I said, I'm quite worried about that just masking a deeper issue with heat generation that could leave me and the Scout trailer stranded.

 

[Charlie207]

I think 200F is normal, especially if the ambient outdoor temps are that high, after that amount of time.

 

[donjetman]

My 6L80 always runs 90-100 degrees hotter than whatever the ambient temp is in the warmer months.
It has a smallish trans cooler - rpo code KNP, not really adequate for towing, but I don't tow so all is good.

 

[15burban]

Do you have factory (before tsb) transmission thermostat still in it? Lookup the tsb on it if you still do. And if you still do have the thermostat a bigger cooler won't do much it will just keep the temperature closer to the temperature the thermostat opens up at.

 

[j91z28d1]

how old is the radiator? Just wondering if the radiator isn't dropping Temps well and you're getting 200deg on the tranny cooler side?

either way I don't believe 200deg shouldn't effect how the tranny shifts and stuff. but I'm no tranny guy. if a big tranny cooler keeps you from a 5-7k rebuild. mask away?

 

[tom3]

If I were in Texas I'd put an aux. cooler on the return line, and a good sized one. and do away with that thermo valve on the trans. On my 6l the highest temps I've seen are just above 180 in jams going (stopping) around Atlanta on a warm day.

 

[CTX-SLPR]

No thermo valve on my 2013 and yes I have looked. Engine coolant temps are holding 210ºF with no variance. The trans temp worries me most as it will regularly get 15-20º hotter here by the depth of summer so if the 90-100º trend follows I'll be well into the hot end of DEX6 and the worst of the symptoms.
Best I know the radiator is original as it only has 117k miles (yes, it nuked the trans under prior ownership at less than 100k miles). A 40k cooler is in the cards for when I'm done rebuilding my friend's Nissan and can get my commuter car back and sideline the Yukon. The question becomes how deep does the hole go with rad, VB, TECHM, etc... to get this thing up to scratch for it's job or do I put an OEM HD cooler on it and trade this in for a 2007 2500 and skip the 6spd mess with a good old 4L80E.

 

[Charlie207]

Do you have factory (before tsb) transmission thermostat still in it? Lookup the tsb on it if you still do. And if you still do have the thermostat a bigger cooler won't do much it will just keep the temperature closer to the temperature the thermostat opens up at.

GMT900s (up to 2014) with the 6L80 don't have the stupid thermostat in the transmission cooler lines. It was added in the 2015s and up.

Edit: part of the confusion stems from trucks - Silverados/Sierras - being updated a year before SUVs. So, a 2014 Silverado would be NNBS, but a 2014 Yukon is still a GMT900.

Corporate Motors ©®™ is first and foremost a truck company.

 

[Charlie207]

No thermo valve on my 2013 and yes I have looked. Engine coolant temps are holding 210ºF with no variance. The trans temp worries me most as it will regularly get 15-20º hotter here by the depth of summer so if the 90-100º trend follows I'll be well into the hot end of DEX6 and the worst of the symptoms.
Best I know the radiator is original as it only has 117k miles (yes, it nuked the trans under prior ownership at less than 100k miles). A 40k cooler is in the cards for when I'm done rebuilding my friend's Nissan and can get my commuter car back and sideline the Yukon. The question becomes how deep does the hole go with rad, VB, TECHM, etc... to get this thing up to scratch for it's job or do I put an OEM HD cooler on it and trade this in for a 2007 2500 and skip the 6spd mess with a good old 4L80E.

The 6L80s are fine. Their issues come from the factory JMBX torque converter, which had a poor design. The back plate would warp over time, and the "hot spots" would shed their friction material into the fluid. This material would block critical ports, orifices, galleys, etc...

They aren't magically going to fail at 200F.

Switching to a billet-backed torque coverter would be cheap & smart insurance. Adding capacity to the fluid would also help, and there are external AT filter kits that are easy to adapt inline with the existing external/aux. coolers.

Understanding the underlying issue, first, then addressing it... that's how you solve a problem. For example: What is the max operation temperature of Dexron VI? It's wayyy more than 200F.

 

[donjetman]

250*f all day everyday is acceptable.
But change the atf at least every 50k miles.

 

[CTX-SLPR]

While DEX6 running that hot may be fine for the fluid, I have shifting issues when I get that hot. Just stacking a cooler on it to hold it down during normal driving only to have it act up when stressed while towing is not where I want to end up. I'm more interested in getting to the bottom of the shifting issues and looking for suggestions on stuff to test. I'm going to put the gauge back on it this weekend so I'll get a recheck of the pump health. If I'm going to drop the whole trans to do a TC I'm probably going to go through the guts as well since it's most of the hard work out done but I'd rather rule things out before getting there.

 

[Foggy]

Do you have factory (before tsb) transmission thermostat still in it? Lookup the tsb on it if you still do. And if you still do have the thermostat a bigger cooler won't do much it will just keep the temperature closer to the temperature the thermostat opens up at.

His year shouldn't have a trans cooler thermostat.. That's a 15 and up on These...
14 and up on the pickups

 

[15burban]

GMT900s (up to 2014) with the 6L80 don't have the stupid thermostat in the transmission cooler lines. It was added in the 2015s and up.

GMT900s (up to 2014) with the 6L80 don't have the stupid thermostat in the transmission cooler lines. It was added in the 2015s and up.

Sorry and thanks guys. I didn't see his model year til now.

 

[Doubeleive]

I was up to 200º within 45min of around town driving at ~85-90º ambient. I only have the factory radiator tank liquid to liquid cooler. The plan is to swap to OEM lines and a Tru-Cool 40K at some point but like I said, I'm quite worried about that just masking a deeper issue with heat generation that could leave me and the Scout trailer stranded.

if it takes 45 minutes for it to get that warmed up that's not all that bad or you just do not drive it that hard, before I added the tru-cool 40k and B&M deep pan I could have mine at 220 in about 5 minutes. now it tops out normally at 180, I can make it hit 190 if I push it in pretty hot weather light to light, anything beyond 190 takes something severe my version of severe is like trying to outrun the motorola block to block.
And if I drive like a sane person it stays anywhere from 145-165, hot idle in the summer is dead on 180

 

[CTX-SLPR]

Regardless I get shifting weirdness at around 195º. What are the likely culprits that start sticking with heat? Things are fine at lower temps like today a 1hr drive in the mid 50ºs and misting was fine with trans temps in the 140ºs. Yes, I'm a pretty relaxed driver but I bought this vs. a minivan because I need to tow and I can't keep it acting normal unloaded so no way I'm going to hitch something to it even with a 40k cooler in the nose. Something is getting hot and acting up and I'd rather try to troubleshoot it before thowing $3.5k at a reman Street Smart unit.

 

[Foggy]

Regardless I get shifting weirdness at around 195º. What are the likely culprits that start sticking with heat? Things are fine at lower temps like today a 1hr drive in the mid 50ºs and misting was fine with trans temps in the 140ºs. Yes, I'm a pretty relaxed driver but I bought this vs. a minivan because I need to tow and I can't keep it acting normal unloaded so no way I'm going to hitch something to it even with a 40k cooler in the nose. Something is getting hot and acting up and I'd rather try to troubleshoot it before thowing $3.5k at a reman Street Smart unit.

Have you put a real scanner on it to check your actual coolant temps under
differing circumstances ??
You may have a cooling issue, not a trans issue....
The gauge on the dash tells you absolutely Zero. It's a modified dummy light.
If your cooling system isn't up to *****, the trans will run hot

 

[CTX-SLPR]

Have you put a real scanner on it to check your actual coolant temps under
differing circumstances ??
You may have a cooling issue, not a trans issue....
The gauge on the dash tells you absolutely Zero. It's a modified dummy light.
If your cooling system isn't up to *****, the trans will run hot

Yes, put a scanner on it and checked the coolant and trans temps dash against the scan values and they were well within in the reading error on the needle and the trans was a fixed 4º offset between the DIC and the scanner. I'll put HPtuners back on it at some point to data log it again but from having a friend watch the scan tool in the passengers seat last fall things agreed pretty well.

 

[Foggy]

Yes, put a scanner on it and checked the coolant and trans temps dash against the scan values and they were well within in the reading error on the needle and the trans was a fixed 4º offset between the DIC and the scanner. I'll put HPtuners back on it at some point to data log it again but from having a friend watch the scan tool in the passengers seat last fall things agreed pretty well.

IF you have it already set up with HPT you should go thru your torque converter settings
and shift scheduling to get rid of some of the crazy crap gm did with those settings