2023 GMC Sierra 3500HD 6.6L Gas/6 Speed - Trans Temps?

[Pryme]

On 8/8/2023 at 8:23 PM, SoCal Angler said:

what is your ambient temp and driving conditions (hwy, city( ?

85 this week. 85 here in the Midwest is more brutal than probably 95 in so cal if that’s where you are. 5-10deg ambient temperature isn’t going to make any difference though. 
 

I run mixed city and hwy. 

[SoCal Angler]

Dealer trans tech inspected and drove truck. 

 

Diagnosis:  NORMAL.

 

I believe @newdude nailed this one!

 

Per dealer notes, " Not able to to duplicate concern.  Accessed diagnostic port and scanned vehicle, found no active or pending codes.  Road tested vehicle for 12 miles and monitored trans temp.  System working as designed.  Trans temp never exceeded 187F and while cruising was maintaining 183F degrees on an 84F day.  No repairs attempted or performed.  System working as designed."

 

I asked about towing 8K-10K trailer in 100F ambient heat with grades and he said no problem.  He further said, depending on conditions, temps may rise up to 225F which is still within normal range.  At 265F trans will send message to driver screen that cool down is needed.

 

I want to thank everyone for their support and technical and personal experience perspective.

 

Alls well, ends well. 

 

Now to start enjoying the truck!

[Grumpy Bear]

32 minutes ago, SoCal Angler said:

I asked about towing 8K-10K trailer in 100F ambient heat with grades and he said no problem.  He further said, depending on conditions, temps may rise up to 225F which is still within normal range.  At 265F trans will send message to driver screen that cool down is needed.

 

Take that with a box of salt. GM also says a quart in 1K miles is normal oil consumption. 

 

I went to the school of common sense and logic. They know high fluid temps are not good for a long life. They lower the TBV setting but the cooling capacity is the same and the parameters of normal are the same? Really? Once the valve is wide open it lives on the heat rejection limit of the cooling system. Nothing changed if 225 F is 'normal'.

 

Get yourself a larger/additional transmission fluid cooler.  Large enough to get the TBV to THROTTLE as it should. Target under 180 F under the worst of the worst. It can't over cool. The TBV won't allow it. 

 

 

[SoCal Angler]

Since it’s under drive train warranty through 2028/60K miles, any mods will void warranty.  That additional cooler will need to wait until then.

 

My concerns have been logged under my VIN with GM.  Not much else I can do at this point.  
 

BTW… what does get TBV to THROTTLE  mean?

 

Also, how do you add fluid to system when adding an additional cooler?

 

 

Edited August 11, 2023 by SoCal Angler

[Pryme]

7 hours ago, Grumpy Bear said:

 

Take that with a box of salt. GM also says a quart in 1K miles is normal oil consumption. 

 

I went to the school of common sense and logic. They know high fluid temps are not good for a long life. They lower the TBV setting but the cooling capacity is the same and the parameters of normal are the same? Really? Once the valve is wide open it lives on the heat rejection limit of the cooling system. Nothing changed if 225 F is 'normal'.

 

Get yourself a larger/additional transmission fluid cooler.  Large enough to get the TBV to THROTTLE as it should. Target under 180 F under the worst of the worst. It can't over cool. The TBV won't allow it. 

 

 

Yeah they also said it was “normal” that my fuel pump primes when I drop the tailgate in the morning. 
 

Just as in this situation, if not every truck experiences something, one of them can’t be correct. Pretty elementary stuff. 

[Grumpy Bear]

8 hours ago, SoCal Angler said:

Since it’s under drive train warranty through 2028/60K miles, any mods will void warranty.  That additional cooler will need to wait until then.

 

My concerns have been logged under my VIN with GM.  Not much else I can do at this point.  
 

BTW… what does get TBV to THROTTLE  mean?

 

Also, how do you add fluid to system when adding an additional cooler?

 

 

 

A thermostat has a 'cracking temperature' and "throttling temperature" and a "wide open" temperature. This constitutes its 'Control range'. 

 

The TBV or thermal Bypass Valve uses the same element STYLE as your radiator water thermostat. A wax pill. And like it, it is designed to maintain a specific temperature. When load increased the valve opens further. When load is removed it closes. If the system is correctly designed, it does this with limited vacillation. The 70 C unit as they chose to call it is fully open by 70C or 158 F. Its range is roughly 20 degrees F so it opens around 138 F and throttles in the low to mid 140's F if it has enough cooler to work with. The original 90 C unit was open fully at 194 F. Opened at 174 F and should have maintained a low 180 F throttling position. It did not. As you have experienced already, neither does the 70C unit. Just not enough base cooling. 

 

A transmission is a heat generator and a heat sink. It sheds heat not only thought the dedicated coolers but the alloy body it is made of as well. This second method is the reason it's hard to overheat in the winters of the north. And why so easy in the summer or under large loads. The OEM has no idea when they design such a system if that unit will be sold in Saudia Arabia or the Northern reaches of Alaska. If you drive 55 or 85. If you tow light or heavy. Mountains or plains. Frankly they couldn't care less as long as it makes it past warranty. 

 

In this graph below (My 6L80E) you see a flat spot between 65 F and 80 F air temperatures. My 70 C TBV is throttling under these conditions. Below that the slop is the effect of radiant cooling in cold air. Likewise, above that area. The difference in 'slope' is a class course in thermal dynamics which I will refrain from explaining here.

 

GM uses several strategies and has changed them a few times to better serve their needs. Keeping you out of the repair bay and you buying new trucks. There is also a governmental consideration. 

 

I need more cooler, and that project is in progress. 

 

 

Part of that strategy is modifying the expectations of what people believe or can be taught to believe is normal. The old frog in a pot of water on the stove parable. 

 

People will tell you this chart is obsolete as advancements in fluids have raised the bar on oxidation. Like any good lie, this is partly true. The fluid is better protected. The seals, clutches and ELECTRONICS however are not! Most of this stuff will take nearly anything for an exceedingly short period of time. Just not continuously. Note how GM has the cut off just at the 'plates start to slip' point? But the seals and gaskets have no such protection? Takes many a trip to that well to kill a seal but kill it, it will. By the time you are out of warranty, damage done. 

 

 

 

Food for thought: What are you protecting? The warranty or the machine? If the warranty, consider this. IF it fails under warranty, it will be replaced or repaired in like and kind, and it WILL fail again and again and again. If it makes THIER goal of just past warranty, you get the bill, and the cycle starts anew. A cycle you can interrupt by protecting the machine instead. Just a thought. Not telling you what to do. 

 

I provide the above as information for your consideration in an effort to assist in making a more broadly informed decision. 

 

 

Edited August 11, 2023 by Grumpy Bear

[Pryme]

20 minutes ago, Grumpy Bear said:

 

A thermostat has a 'cracking temperature' and "throttling temperature" and a "wide open" temperature. This constitutes its 'Control range'. 

 

The TBV or thermal Bypass Valve uses the same element STYLE as your radiator water thermostat. A wax pill. And like it, it is designed to maintain a specific temperature. When load increased the valve opens further. When load is removed it closes. If the system is correctly designed, it does this with limited vacillation. The 70 C unit as they chose to call it is fully open by 70C or 158 F. Its range is roughly 20 degrees F so it opens around 138 F and throttles in the low to mid 140's F if it has enough cooler to work with. The original 90 C unit was open fully at 194 F. Opened at 174 F and should have maintained a low 180 F throttling position. It did not. As you have experienced already, neither does the 70C unit. Just not enough base cooling. 

 

A transmission is a heat generator and a heat sink. It sheds heat not only thought the dedicated coolers but the alloy body it is made of as well. This second method is the reason it's hard to overheat in the winters of the north. And why so easy in the summer or under large loads. The OEM has no idea when they design such a system if that unit will be sold in Saudia Arabia or the Northern reaches of Alaska. If you drive 55 or 85. If you tow light or heavy. Mountains or plains. Frankly they couldn't care less as long as it makes it past warranty. 

 

In this graph below (My 6L80E) you see a flat spot between 65 F and 80 F air temperatures. My 70 C TBV is throttling under these conditions. Below that the slop is the effect of radiant cooling in cold air. Likewise, above that area. The difference in 'slope' is a class course in thermal dynamics which I will refrain from explaining here.

 

GM uses several strategies and has changed them a few times to better serve their needs. Keeping you out of the repair bay and you buying new trucks. There is also a governmental consideration. 

 

I need more cooler, and that project is in progress. 

 

 

Part of that strategy is modifying the expectations of what people believe or can be taught to believe is normal. The old frog in a pot of water on the stove parable. 

 

People will tell you this chart is obsolete as advancements in fluids have raised the bar on oxidation. Like any good lie, this is partly true. The fluid is better protected. The seals, clutches and ELECTRONICS however are not! Most of this stuff will take nearly anything for an exceedingly short period of time. Just not continuously. Note how GM has the cut off just at the 'plates start to slip' point? But the seals and gaskets have no such protection? Takes many a trip to that well to kill a seal but kill it, it will. By the time you are out of warranty, damage done. 

 

 

 

Food for thought: What are you protecting? The warranty or the machine? If the warranty, consider this. IF it fails under warranty, it will be replaced or repaired in like and kind, and it WILL fail again and again and again. If it makes THIER goal of just past warranty, you get the bill, and the cycle starts anew. A cycle you can interrupt by protecting the machine instead. Just a thought. Not telling you what to do. 

 

I provide the above as information for your consideration in an effort to assist in making a more broadly informed decision. 

 

 

Excellent information and graph. 
 

 

[Grumpy Bear]

Oil cooler bypass valve actuating means - Lockhart Industries, Inc. (freepatentsonline.com)

 

Lockhart owns the patent on the valve style. Or use to. I expect it has run out. Technical but worth a read if you are interested in such things. 

 

I have a new in box Lockhart cooler I was going to toss. Then I found out they are bringing close to $300! 

[SoCal Angler]

2 hours ago, Grumpy Bear said:

 

A thermostat has a 'cracking temperature' and "throttling temperature" and a "wide open" temperature. This constitutes its 'Control range'. 

 

The TBV or thermal Bypass Valve uses the same element STYLE as your radiator water thermostat. A wax pill. And like it, it is designed to maintain a specific temperature. When load increased the valve opens further. When load is removed it closes. If the system is correctly designed, it does this with limited vacillation. The 70 C unit as they chose to call it is fully open by 70C or 158 F. Its range is roughly 20 degrees F so it opens around 138 F and throttles in the low to mid 140's F if it has enough cooler to work with. The original 90 C unit was open fully at 194 F. Opened at 174 F and should have maintained a low 180 F throttling position. It did not. As you have experienced already, neither does the 70C unit. Just not enough base cooling. 

 

A transmission is a heat generator and a heat sink. It sheds heat not only thought the dedicated coolers but the alloy body it is made of as well. This second method is the reason it's hard to overheat in the winters of the north. And why so easy in the summer or under large loads. The OEM has no idea when they design such a system if that unit will be sold in Saudia Arabia or the Northern reaches of Alaska. If you drive 55 or 85. If you tow light or heavy. Mountains or plains. Frankly they couldn't care less as long as it makes it past warranty. 

 

In this graph below (My 6L80E) you see a flat spot between 65 F and 80 F air temperatures. My 70 C TBV is throttling under these conditions. Below that the slop is the effect of radiant cooling in cold air. Likewise, above that area. The difference in 'slope' is a class course in thermal dynamics which I will refrain from explaining here.

 

GM uses several strategies and has changed them a few times to better serve their needs. Keeping you out of the repair bay and you buying new trucks. There is also a governmental consideration. 

 

I need more cooler, and that project is in progress. 

 

 

Part of that strategy is modifying the expectations of what people believe or can be taught to believe is normal. The old frog in a pot of water on the stove parable. 

 

People will tell you this chart is obsolete as advancements in fluids have raised the bar on oxidation. Like any good lie, this is partly true. The fluid is better protected. The seals, clutches and ELECTRONICS however are not! Most of this stuff will take nearly anything for an exceedingly short period of time. Just not continuously. Note how GM has the cut off just at the 'plates start to slip' point? But the seals and gaskets have no such protection? Takes many a trip to that well to kill a seal but kill it, it will. By the time you are out of warranty, damage done. 

 

 

 

Food for thought: What are you protecting? The warranty or the machine? If the warranty, consider this. IF it fails under warranty, it will be replaced or repaired in like and kind, and it WILL fail again and again and again. If it makes THIER goal of just past warranty, you get the bill, and the cycle starts anew. A cycle you can interrupt by protecting the machine instead. Just a thought. Not telling you what to do. 

 

I provide the above as information for your consideration in an effort to assist in making a more broadly informed decision. 

 

 

Thanks for the info and graph...very helpful

 

So...to understand the "Control Range" and its terms clearly, "Throttling" is between 65F-80F, "Cracking" is below 65F-80F, and "Wide Open" is above 65F-80F...correct?

 

Also, when an additional cooler is added, how is additional trans fluid added to system?

Edited August 11, 2023 by SoCal Angler

[Grumpy Bear]

1 hour ago, SoCal Angler said:

Thanks for the info and graph...very helpful

 

So...to understand the "Control Range" and its terms clearly, "Throttling" is between 65F-80F, "Cracking" is below 65F-80F, and "Wide Open" is above 65F-80F...correct?

 

Also, when an additional cooler is added, how is additional trans fluid added to system?

 

Not quite. Air temperature has an effect on ATF temperature, just like load and speed. The TBV responds to the fluid not the air temperature. Dog wag his tail the tail doesn't wag the dog. That graph was tied to 55 mph. I can move that curve with speed or load. I isolated the variables controling speed and load so that only air temperature was the lever. 3 years of data are shown in that graph. I did that after isolating the speeds effect on cooling. Checking it against standard engineering formulas. Pretty darn close to them I'd say. 

 

Thus cracking, throttling and fully open are functions of ATF temps not air temps. Air temps influence how much heat is removed as does air velocity. Why it's important to keep the AC condenser clean as well as the trans cooler, if air to air and the radiator if liquid to liquid. You get best cooling around 25 meters per second which is 55.92 mph or 90 kph. 

 

To your other question. @newdude could answer that better than I. I don't know the particulars of every variation out there. He's a tech and does. Sorry. 

[newdude]

2 hours ago, SoCal Angler said:

Thanks for the info and graph...very helpful

 

So...to understand the "Control Range" and its terms clearly, "Throttling" is between 65F-80F, "Cracking" is below 65F-80F, and "Wide Open" is above 65F-80F...correct?

 

Also, when an additional cooler is added, how is additional trans fluid added to system?

 

 

You'd perform a fluid level check just like for the factory fill.  Level is set via a check plug in the pan.  It probably won't take a whole lot more I'd think if a larger cooler were installed.  A deep pan would add much more fluid than a larger cooler.  

 

27 minutes ago, Grumpy Bear said:

 

Not quite. Air temperature has an effect on ATF temperature, just like load and speed. The TBV responds to the fluid not the air temperature. Dog wag his tail the tail doesn't wag the dog. That graph was tied to 55 mph. I can move that curve with speed or load. I isolated the variables controling speed and load so that only air temperature was the lever. 3 years of data are shown in that graph. I did that after isolating the speeds effect on cooling. Checking it against standard engineering formulas. Pretty darn close to them I'd say. 

 

Thus cracking, throttling and fully open are functions of ATF temps not air temps. Air temps influence how much heat is removed as does air velocity. Why it's important to keep the AC condenser clean as well as the trans cooler, if air to air and the radiator if liquid to liquid. You get best cooling around 25 meters per second which is 55.92 mph or 90 kph. 

 

To your other question. @newdude could answer that better than I. I don't know the particulars of every variation out there. He's a tech and does. Sorry. 

 

All I can find on the OE TBVs, both the original 90C and the replacement 70C units from GM. 

 

Information on Transmission Thermal By-Pass Valve (TBV) operation:

The TBV starts to open between 180 to 187 F ( 82-86 C).

The TBV is fully opened at 194 F (90 C).

 

Note: If the TBV has been replaced following TSB 21-NA-199, the operating temperature will be lower.

The TBV starts to open between 138 to 145 F (59-63 C).

The TBV is fully opened at 158 F (70 C).

 

And the diag on TBV operations:

 

Diagnosis:

• Drive the vehicle long enough to bring the transmission fluid temperature up to 190 F to insure the TBV is open.
• Use an infrared thermometer and check the temperature of the pan surface.
• Compare the pan temperature to the transmission temperature in the scan tool data. The pan temperature and the transmission data temperature should be close to the same.
• Use the infrared thermometer to check the temperature of the TBV. 
• Use the infrared thermometer to check the temperature of both cooler lines about 6 inches away from the TBV.
• The cooler line going to the cooler will be higher than the pan temperature.
• If the cooling system is working correctly the cooler return line will be lower in temperature than the line going to the cooler.
• If the TBV is not opening both cooler lines temperatures will be lower than the transmission pan temperature and the TBV temperature will be higher than the pan temperature. 

[SoCal Angler]

20 minutes ago, newdude said:

 

 

You'd perform a fluid level check just like for the factory fill.  Level is set via a check plug in the pan.  It probably won't take a whole lot more I'd think if a larger cooler were installed.  A deep pan would add much more fluid than a larger cooler.  

 

 

All I can find on the OE TBVs, both the original 90C and the replacement 70C units from GM. 

 

Information on Transmission Thermal By-Pass Valve (TBV) operation:

The TBV starts to open between 180 to 187 F ( 82-86 C).

The TBV is fully opened at 194 F (90 C).

 

Note: If the TBV has been replaced following TSB 21-NA-199, the operating temperature will be lower.

The TBV starts to open between 138 to 145 F (59-63 C).

The TBV is fully opened at 158 F (70 C).

 

And the diag on TBV operations:

 

Diagnosis:

• Drive the vehicle long enough to bring the transmission fluid temperature up to 190 F to insure the TBV is open.
• Use an infrared thermometer and check the temperature of the pan surface.
• Compare the pan temperature to the transmission temperature in the scan tool data. The pan temperature and the transmission data temperature should be close to the same.
• Use the infrared thermometer to check the temperature of the TBV. 
• Use the infrared thermometer to check the temperature of both cooler lines about 6 inches away from the TBV.
• The cooler line going to the cooler will be higher than the pan temperature.
• If the cooling system is working correctly the cooler return line will be lower in temperature than the line going to the cooler.
• If the TBV is not opening both cooler lines temperatures will be lower than the transmission pan temperature and the TBV temperature will be higher than the pan temperature. 

 

 

Thanks newdude!  Your diagnosis makes sense.  Dealer did not perform that diagnosis.  BTW.. is your diagnosis method a GM diagnosis for the 6L90 that should be performed by dealers? Perhaps since temps did not appear abnormal during drive time, the diagnostic steps you mentioned were not carried out?

 

I could probably perform your diagnosis myself, but using trans temp on dash, as I have no GM scan tool. Since trans temps on dash are coming from PCM, wouldn't it be as accurate, or is scan tool toll pulling temps from somewhere else?

 

As far as adding additional fluid vs additional cooler....

 

Is it additional fluid or additional air to fluid (or both) that reduces trans temps more efficiently?

 

Wouldn't the additional fluid also take monger to cool down due increase quantity?

Also, wouldn't there be no additional benefit from air to fluid that an additional cooler would provide?

Edited August 11, 2023 by SoCal Angler

[newdude]

7 hours ago, SoCal Angler said:

 

 

Thanks newdude!  Your diagnosis makes sense.  Dealer did not perform that diagnosis.  BTW.. is your diagnosis method a GM diagnosis for the 6L90 that should be performed by dealers? Perhaps since temps did not appear abnormal during drive time, the diagnostic steps you mentioned were not carried out?

 

I could probably perform your diagnosis myself, but using trans temp on dash, as I have no GM scan tool. Since trans temps on dash are coming from PCM, wouldn't it be as accurate, or is scan tool toll pulling temps from somewhere else?

 

As far as adding additional fluid vs additional cooler....

 

Is it additional fluid or additional air to fluid (or both) that reduces trans temps more efficiently?

 

Wouldn't the additional fluid also take monger to cool down due increase quantity?

Also, wouldn't there be no additional benefit from air to fluid that an additional cooler would provide?

 

 

The gauge on the dash should be reading from the TCM if I'm not mistaken.  The temp sensor is part of the TCM.  TCM = Transmission Control Module.

 

I can't really speak on more fluid with a deeper pan or larger cooler or both combined.  I do know that doing what is known as the "pill flip" which is a flip of the thermostat internals of the TBV to allow the transmission to flow continuously greatly reduces operating temperatures of the transmissions.  It renders the cooling loop like all the gas HDs prior that were continuous flow without a bypass.  

If you are concerned especially if you tow a lot, I'd start with the pill flip first, assuming it can still be done on the 2020-2023 TBV.  

[Grumpy Bear]

7 hours ago, SoCal Angler said:

Wouldn't the additional fluid also take monger (longer?) to cool down due increase quantity?

Also, wouldn't there be no additional benefit from air to fluid that an additional cooler would provide?

 

You are a curious one.  Good! 

 

Doing as @newdude suggest will bring the unloaded temperature down. But it won't keep it down when under load. Sensible temperature is BTU's in minus BTU's out and this system does not have enough BTU's out capacity.

 

A BTU is the amount of heat energy required to raise one pound of water one degree. A BTU hour is the same definition over time. That is; one BTU hour is the energy required to raise a pound of water one degree in one hour. The time element is important. If you stop, shut the rig down, your transmission will cool to ambient temperature over some period of time, like overnight.

 

When towing you are heating and the hotter it gets the harder it is for the system to dissipate that heat. A pill flip allows one to get all the system has to give but it is still not enough on a hot day towing a larger load up a steep grade as a speed that is not ideal for an air to fluid system. 

 

The simplest way I know how to say this is; Add cooler until you get the temperature you seek under the worst conditions you expect to encounter. 

 

IMHO 160 F as a peak is a great target. Lots of shops will tell you 175 F To 180 F. Many systems are designed with that number in mind. The fact GM designed the new valve to be fully open by 158 F tells me that I'm closer to the truth than many. 

 

If I were a bodyguard, I would think my job is not to see how close to the edge of the cliff I can let you get without falling over but rather how far from the cliff I can keep you...thus safe. 

 

 

 

 

[SoCal Angler]

1 hour ago, newdude said:

 

 

The gauge on the dash should be reading from the TCM if I'm not mistaken.  The temp sensor is part of the TCM.  TCM = Transmission Control Module.

 

I can't really speak on more fluid with a deeper pan or larger cooler or both combined.  I do know that doing what is known as the "pill flip" which is a flip of the thermostat internals of the TBV to allow the transmission to flow continuously greatly reduces operating temperatures of the transmissions.  It renders the cooling loop like all the gas HDs prior that were continuous flow without a bypass.  

If you are concerned especially if you tow a lot, I'd start with the pill flip first, assuming it can still be done on the 2020-2023 TBV.  

 

 

Thanks.  I think for now, I'll tow my trailer next month on a 350 mile camping trip (one way) and see how it goes.  Trailer is 7500# GVWR, plus 3-4 passengers and gear in truck bed which is about 8700# total, and see how it goes.  There are a few grades on the way.  I'm sure ambient temps will still be in in the high 90s.  This trip should give trans a good test.

 

Ill need to find out somewhere if flipping the pill on the new 70C TBV is the same as the previous TBV (90C), in that it eliminates the thermostat completely and the fluid runs in/out of trans completely unrestricted.  In this mod, I believe the TBV housing (aluminum block) has been reduced to a simple housing for the trans lines to enter/exit the trans...correct?  

 

Thanks