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

SoCal Angler · August 6, 2023

Hello all-

Just purchased a new 2023 GMC 3500 HD with 6.6L gas and 6 speed auto.

Trans is model 6L90.

I checked, and trans does have the latest CBV (Cooler Bypass Valve (with the "70" imprinted on the bottom of it).

What are the normal operating temps.....for various ambient temps?

Ex. Unloaded temps since truck is new and had not been broken in just yet. These temps are from 21 miles on odometer to 220 miles:

114F ambient: highway and some stop and go....trans temp was approx. 195F-200F unloaded. Did reach 200F when climbing a slight grade that was about 4-5 miles long. Stopped in a parking lot to grab a bite to eat, and it climbed to 205F. Left trans in Park and let engine idle until it reached 199 before turning off motor.

100F ambient: around town...reaches 195F.

Are these normal considering ambient temps?
Are they high due to being new and not broken in?
They seem high to me, but I have no experience with GM trannies.

NOTE: I'm new to GMC and my only trans temp experience has been with my last Ford trans (4R100) with updated 6.0L cooler, had temps always just under 200 when towing 8K in 100F

Thanks!

Grumpy Bear · August 6, 2023

Given the days temperatures it did pretty good. That said if were that hot ever day I'd be looking for additional cooler.

Pryme · August 7, 2023

Mine sits at 151deg unloaded daily. Been up to 92 this last week with real feel of 98. Yours is running way hot. I’ve never seen it go above 170

the8rotor · August 7, 2023

1 hour ago, Pryme said:

Mine sits at 151deg unloaded daily. Been up to 92 this last week with real feel of 98. Yours is running way hot. I’ve never seen it go above 170

I second this. My 2021 gmc 2500 with the 6L90 never went over 174 down here in Texas unloaded. Towing in this heat is when I'd sniff the 200 degree mark.

SoCal Angler · August 7, 2023

Going to call and take it in to dealer this week. See what they say. I printed two TSBs that are related to the 6L90 and high trans temps...

TSB 21-NA-199

TSB 22-NA-182

Another JR · August 7, 2023

TSB-21-NA-199 is just the bypass valve change from 195 to 150.

I noted that you have a valve marked as a new valve, but I find it suspicious that your temperatures are exactly how mine acts with the old 195F bypass valve. Makes me wonder if you received a mislabeled old valve.

Edited August 7, 2023 by Another JR

SoCal Angler · August 7, 2023

Called a dealer about 45 mins away in another city. I have one closer in my own city, but I've heard great things about the other.

Explained my concerns to the Service Advisor. I gave him the 2 TSBs I was reading about, my concerns about towing in this heat, and that I may have a bad

"70" CBV (TSB)
Twisted trans line (TSB)
Stuck CBV
Or something else.

He said he would check with trans tech and get back to me.

An hour later, he said according to trans tech....

Temps were not totally out of parameters considering ambient temps.
He also said it could be a faulty CBV or CBV getting stuck. He's never seen twisted lines.

I asked how he would be checking to see if CBV was bad or stuck....he said they would connect truck to their Scan Tool and it would tell them at what temps CBV fully opens.

He said he will work with scheduler for an appointment and would get back to me with a date to bring it in. He said be prepared for truck to be at dealer for two weeks, as they work on them in order of appt and arrival and truck will only be seen by a trans tech (dealer has three trans techs).

I asked about a car rental for the time they will have the truck, seeing as my truck is new. He said he would check with service manager to see if that's possible. They may not cover a rental car, as I did not purchase the truck from this dealer. I purchased my truck from a dealer 150 miles away from my home. I can take it to them, but that is a 300 miles round trip. It may come to that, but I'd rather keep warranty work a little closer to home.

BTW....Does GM cover rental cars when they have a truck in for warranty work that requires more than one day for repair work?

Thanks!

Edited August 7, 2023 by SoCal Angler

Pryme · August 7, 2023

It’s way out of parameter. I thought of this thread and watched close today. It’s 83 today, not that ambient temperature makes any difference, and it never went over 154.
It gets to its set point no matter what the ambient temperature is. Unless it’s crazy cold and I don’t drive far.

two weeks? They might as well said “we don’t want you to come in here at all”

I know it’s warranty work but a good independent shop would have it done in a day I’m sure.

Cant warranty work be done outside a dealership and have it billed to gm?

SoCal Angler · August 7, 2023

Called a dealer about 45 mins away in another city. I have one closer in my own city, but I've heard great things about the other.

Explained my concerns to the Service Advisor. I gave him the 2 TSBs I was reading about, my concerns about towing in this heat, and that I may have a bad

"70" CBV (TSB)
Twisted trans line (TSB)
Stuck CBV
Or something else.

He said he would check with trans tech and get back to me.

An hour later, he said according to trans tech....

Temps were not totally out of parameters considering ambient temps.
He also said it could be a faulty CBV or CBV getting stuck. He's never seen twisted lines.

I asked how he would be checking to see if CBV was bad or stuck....he said they would connect truck to their Scan Tool and it would tell them at what temps CBV fully opens.

He said he will work with scheduler for an appointment and would get back to me with a date to bring it in. He said be prepared for truck to be at dealer for two weeks, as they work on them in order of appt and arrival and truck will only be seen by a trans tech (dealer has three trans techs).

I asked about a car rental for the time they will have the truck, seeing as my truck is new. He said he would check with service manager to see if that's possible. They may not cover a rental car, as I did not purchase the truck from this dealer. I purchased my truck from a dealer 150 miles away from my home. I can take it to them, but that is a 300 miles round trip. It may come to that, but I'd rather keep warranty work a little closer to home.

BTW....Does GM cover rental cars when they have truck in for warranty work that requires more than one day for repair work?

Thanks!

Another JR · August 8, 2023

2 hours ago, Pryme said:

It’s way out of parameter. I thought of this thread and watched close today. It’s 83 today, not that ambient temperature makes any difference, and it never went over 154.
It gets to its set point no matter what the ambient temperature is. Unless it’s crazy cold and I don’t drive far.

two weeks? They might as well said “we don’t want you to come in here at all”

I know it’s warranty work but a good independent shop would have it done in a day I’m sure.

Cant warranty work be done outside a dealership and have it billed to gm?

From what he described, it’s operating just as you are describing, but with a thermostat set at 195F. That’s way too suspicious given that’s the old valve setpoint. I’ll bet he has a mismarked valve.

newdude · August 8, 2023

On 8/6/2023 at 6:06 PM, SoCal Angler said:

Hello all-

Just purchased a new 2023 GMC 3500 HD with 6.6L gas and 6 speed auto.

Trans is model 6L90.

I checked, and trans does have the latest CBV (Cooler Bypass Valve (with the "70" imprinted on the bottom of it).

What are the normal operating temps.....for various ambient temps?

Ex. Unloaded temps since truck is new and had not been broken in just yet. These temps are from 21 miles on odometer to 220 miles:

114F ambient: highway and some stop and go....trans temp was approx. 195F-200F unloaded. Did reach 200F when climbing a slight grade that was about 4-5 miles long. Stopped in a parking lot to grab a bite to eat, and it climbed to 205F. Left trans in Park and let engine idle until it reached 199 before turning off motor.

100F ambient: around town...reaches 195F.

Are these normal considering ambient temps?
Are they high due to being new and not broken in?
They seem high to me, but I have no experience with GM trannies.

NOTE: I'm new to GMC and my only trans temp experience has been with my last Ford trans (4R100) with updated 6.0L cooler, had temps always just under 200 when towing 8K in 100F

Thanks!

Sounds normal. If its stamped "70" its the lower temp. The "90" valves were installed 2021 and prior.

Truck is new, high ambient temperatures have an effect here as well, especially 100F-114F.

21-NA-199 won't apply here because you've got the "70" valve. Put some more miles on it and see how the temps are. If the TBV were sticking or a cooler line were twisted, you'd see WAY higher than 200F and you'd see it VERY quick. Like you'd hit the overheat warning real quick to 265F or higher.

Edited August 8, 2023 by newdude

Pryme · August 8, 2023

42 minutes ago, newdude said:

Sounds normal. If its stamped "70" its the lower temp. The "90" valves were installed 2021 and prior.

Truck is new, high ambient temperatures have an effect here as well, especially 100F-114F.

21-NA-199 won't apply here because you've got the "70" valve. Put some more miles on it and see how the temps are. If the TBV were sticking or a cooler line were twisted, you'd see WAY higher than 200F and you'd see it VERY quick. Like you'd hit the overheat warning real quick to 265F or higher.

I’m just not sure why these trucks with the same transmission have two different set points so different. Mid 150’s and mid 190’s is a huge difference

Ray Pickle · August 8, 2023

I see 190 to 205 towing as normal pulling 12k fiver.

newdude · August 8, 2023

6 minutes ago, Pryme said:

I’m just not sure why these trucks with the same transmission have two different set points so different. Mid 150’s and mid 190’s is a huge difference

GM being GM, the TBV temp on 2020-2021 HD was factory 90C/194F. After all the issues broke out with converters and failures on 6L80/90 units, they revised the TBV temp to 70C/158F. All production HD from whatever breakpoint forward so I "think" mid/late 2021 and onwards are the 70C/158F temp TBVs.

Pryme · August 8, 2023

21 minutes ago, newdude said:

GM being GM, the TBV temp on 2020-2021 HD was factory 90C/194F. After all the issues broke out with converters and failures on 6L80/90 units, they revised the TBV temp to 70C/158F. All production HD from whatever breakpoint forward so I "think" mid/late 2021 and onwards are the 70C/158F temp TBVs.

Well I’m glad I have the 158 and would make the change if I had the 194. Just seems better to run a bit cooler for longevity. Just my feeling on it.