Duramax Transmission Temp?

overkill19

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So I bought this 2008 3500HD with 100000miles on it. I’ve been going through it fixing stuff as I go.
Did the hydroboost upgrade and a fluid flush. Switched over to Amsoil.
Did a tcase fluid change to Amsoil too
I had a transmission cooler leak so I’ve been checking my level while waiting on parts.
My manual says temp should be at 140F ish.
Well I can’t get over 122 no matter what I do, drive on highway, in town I can’t get it any higher.
Also my manual says check level in park, I thought it should be in neutral? Anyone have any ideas? I might order a complete filter/ fluid change while doing the lines.


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acesup800

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So I bought this 2008 3500HD with 100000miles on it. I’ve been going through it fixing stuff as I go.
Did the hydroboost upgrade and a fluid flush. Switched over to Amsoil.
Did a tcase fluid change to Amsoil too
I had a transmission cooler leak so I’ve been checking my level while waiting on parts.
My manual says temp should be at 140F ish.
Well I can’t get over 122 no matter what I do, drive on highway, in town I can’t get it any higher.
Also my manual says check level in park, I thought it should be in neutral? Anyone have any ideas? I might order a complete filter/ fluid change while doing the lines.


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Checking level should be running in Park. The cooler the temps the better. My 2016 temp runs 95F on the highway and as high as 180F pulling if running through some gears. I think they are safe up to 210F for short periods of time.
 

ABMax24

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It's winter, nothing to worry about.

IIRC the 6 speed Allison is good to 240F. The 6R140 in my Powerstroke hits 230F on a regular basis when towing.

I can't remember what year the cutoff was, but some of the older Allison's used to be a little picky with transmission fluid, because the TES 295 (Allison Spec) fluid is not quite the same as the Dex-VI fluid that GM recommended. I used to run a modded 5 speed Allison and most of the transmission builders at that time swore by Castrol Transynd (which was also what Allison shipped the tranny from the factory with). But any TES 295 or TES 668 (new updated spec) would meet the requirements.

Here's Allison's list: (296 and 668 are both selectable)
 

overkill19

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Checking level should be running in Park. The cooler the temps the better. My 2016 temp runs 95F on the highway and as high as 180F pulling if running through some gears. I think they are safe up to 210F for short periods of time.

Having a tough time getting a consistent level check.
Checked it cold, in park, it shows way overfilled.
When it up to 120, go through each gear let it idle. it shows too low.I add some, go for a drive come back let it idle after going through each gear while parked then idle for 5 min. It shows way overfilled. Some of the you tube videos say only check in neutral but my manual clearly says in park.


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LMLCHEVY

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I’m assuming this truck has an Allison trans in it?

Park is just neutral with the parking pawl engaged in most vehicles. Run it up to temp or as warm as it’s gonna get and then check it on level ground. Overfilling it is usually not a good thing as it will cause it to overheat.
 

overkill19

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As long as the transmission isn't overheating, that's all that matters! If it aint broke, don't fix it. Probably good idea to change trans fluid/filter anyway.

Fluid looks great but figured with Transmission cooler lines needing to be done. I figured do it all at once.
I was getting very erratic levels but went for a good drive today twice and got good hot readings.

Found it strange the manual says check fluid at 140F and when I can’t hit 120F I was worried maybe I had a fan clutch stuck and cooling too much.


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Mountainman52

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It is winter out and unless you have your motor and trans under a steady load going to be vary hard to reach normal temps. on a diesel in winter maybe with the winterfront all buttoned up.
 

Kyle89

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I don't really look at Temps in winter but summer when towing can see 190-200* pulling hills. I use trans-synd , have 410xxx kms on my 07.5 lmm

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LMLCHEVY

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It's winter, nothing to worry about.

IIRC the 6 speed Allison is good to 240F. The 6R140 in my Powerstroke hits 230F on a regular basis when towing.

I can't remember what year the cutoff was, but some of the older Allison's used to be a little picky with transmission fluid, because the TES 295 (Allison Spec) fluid is not quite the same as the Dex-VI fluid that GM recommended. I used to run a modded 5 speed Allison and most of the transmission builders at that time swore by Castrol Transynd (which was also what Allison shipped the tranny from the factory with). But any TES 295 or TES 668 (new updated spec) would meet the requirements.

Here's Allison's list: (296 and 668 are both selectable)
All Dmax with a 6 speed have been coming with Dex VI TES-668. The 5 speeds got the Dex III TES-296. DEX VI can be used in the 5 speeds without issue. 6 speeds can run Dex III but you will have to change the oil more frequently and they aren’t as fond of the heat as Dex VI.

120 degrees is fine in the winter for any Allison. Only thing you might see is cooler engine temps as it will draw heat from the exchanger in the rad. I’ve owned every model of dmax except the L5P and never had issues with trans heat in any of them. Just keep the fluid at the right level and change your spin on as recommended in the manual.
 

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I cant help but laugh at this...
Is my tranny too cold ???

No. Dont even worry about temps till you see 200 imo
 

2kDoo

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180 in summer is very normal too
 

ABMax24

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All Dmax with a 6 speed have been coming with Dex VI TES-668. The 5 speeds got the Dex III TES-296. DEX VI can be used in the 5 speeds without issue. 6 speeds can run Dex III but you will have to change the oil more frequently and they aren’t as fond of the heat as Dex VI.

120 degrees is fine in the winter for any Allison. Only thing you might see is cooler engine temps as it will draw heat from the exchanger in the rad. I’ve owned every model of dmax except the L5P and never had issues with trans heat in any of them. Just keep the fluid at the right level and change your spin on as recommended in the manual.

Unfortunately your information is incorrect, although it is the some of the same incorrect information also perpetuated by GM.

The factory fills were Castrol Transynd TES-295, this fluid just happens to be Dex III compatible, Castrol Transynd TES-295 was never Dex VI rated. The 5 speed and 6 speed never got TES-668 as a factory fill, that fluid spec came along in late 2020, after the 6 speed was replaced with the 10 speed.

Dex VI is not universally acceptable in all 5 speed Allisons, there was a cutoff date at some point in the manufacture of the 5 speeds because certain seals in the transmission are not compatible with additives in Dex VI fluids, causing deterioration and fluid leaks, Dex III doesn't cause this issue, although good luck finding straight Dex III these days, TES-295 would be the solution here. Allison released a TSB to this effect. My understanding is the seal in question was made of Viton and Dex VI is incompatible with Viton.

Second, is GM itself recommends the use of TES-295 (Now TES-668) fluids in 6 speeds operated below -40c, most people in this area should be running Allison approved fluids based solely on that.

TES-295 and Dex III or Dex VI are not the same fluid, there's lots of info on this online if people want to look.

Ultimately people can run whatever they want in their transmissions, there's literally millions of trucks running a mix of Dex VI and TES295 based on GM's advice. However GM's engineers weren't capable of building these transmissions, so I wouldn't trust their advice on the fluids for them either. Allison built the transmission around their fluid spec so that's what I ran in mine.
 

LMLCHEVY

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Unfortunately your information is incorrect, although it is the some of the same incorrect information also perpetuated by GM.

The factory fills were Castrol Transynd TES-295, this fluid just happens to be Dex III compatible, Castrol Transynd TES-295 was never Dex VI rated. The 5 speed and 6 speed never got TES-668 as a factory fill, that fluid spec came along in late 2020, after the 6 speed was replaced with the 10 speed.

Dex VI is not universally acceptable in all 5 speed Allisons, there was a cutoff date at some point in the manufacture of the 5 speeds because certain seals in the transmission are not compatible with additives in Dex VI fluids, causing deterioration and fluid leaks, Dex III doesn't cause this issue, although good luck finding straight Dex III these days, TES-295 would be the solution here. Allison released a TSB to this effect. My understanding is the seal in question was made of Viton and Dex VI is incompatible with Viton.

Second, is GM itself recommends the use of TES-295 (Now TES-668) fluids in 6 speeds operated below -40c, most people in this area should be running Allison approved fluids based solely on that.

TES-295 and Dex III or Dex VI are not the same fluid, there's lots of info on this online if people want to look.

Ultimately people can run whatever they want in their transmissions, there's literally millions of trucks running a mix of Dex VI and TES295 based on GM's advice. However GM's engineers weren't capable of building these transmissions, so I wouldn't trust their advice on the fluids for them either. Allison built the transmission around their fluid spec so that's what I ran in mine.
If you say so.
I am incorrect on the 668. It came factory filled standard in MY’21 as you said. My mistake.

But the rest of what you said isn’t 100% correct either. The cutoff in the transmission s/n was for those that got the viton seals. Synthetic and synthetic blend oils accelerated the hardening of these seals, but it was over many years of running the Dex VI, not weeks and time has shown they would harden prematurely even with dex III. Therefore nowadays it’s common to just run dex VI or a 295 or 668 oil and I haven’t heard of any issues attributed to the oil choice.

Also even Allison said DEX VI is ok to run not just GM. I would recommend the 295 or 668 myself though.

From Allison:
allison transmission recommends that customers use an allison approved tes 295 automatic transmission fluid to extend drain intervals and to enhance transmission performance and durability in all operating environments. Customers may continue to choose from a wide variety of allison approved fluids.
effective January 1, 2007, general motors no longer licenses deXRon®-iii fluids. deXRon®-Vi fluids may be used in the 1000 and 2000 Product Families transmissions beginning with s/n 6310670488 and 6320784373

 

ABMax24

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If you say so.
I am incorrect on the 668. It came factory filled standard in MY’21 as you said. My mistake.

But the rest of what you said isn’t 100% correct either. The cutoff in the transmission s/n was for those that got the viton seals. Synthetic and synthetic blend oils accelerated the hardening of these seals, but it was over many years of running the Dex VI, not weeks and time has shown they would harden prematurely even with dex III. Therefore nowadays it’s common to just run dex VI or a 295 or 668 oil and I haven’t heard of any issues attributed to the oil choice.

Also even Allison said DEX VI is ok to run not just GM. I would recommend the 295 or 668 myself though.

From Allison:
allison transmission recommends that customers use an allison approved tes 295 automatic transmission fluid to extend drain intervals and to enhance transmission performance and durability in all operating environments. Customers may continue to choose from a wide variety of allison approved fluids.
effective January 1, 2007, general motors no longer licenses deXRon®-iii fluids. deXRon®-Vi fluids may be used in the 1000 and 2000 Product Families transmissions beginning with s/n 6310670488 and 6320784373


We're pretty much saying the same thing. The S/N cutoff is the same thing I wrote, there was a mfg date where the assembly line switched away from Viton seals, there's 2 serial numbers because the Baltimore and Indianapolis plants switched at different dates and had their own unique serial codes.

Yes Allison says you can run Dex VI in their transmissions, but the fluid change interval drops to 1/3 for mileage and 1/2 based on engine hours when compared to TES295.
 
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overkill19

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I cant help but laugh at this...
Is my tranny too cold ???

No. Dont even worry about temps till you see 200 imo
Personally I don't agree.
If temp is reading too low could it not be a bad thermocouple? So when you hit 200 you could be 250...300 who knows. I've learned a long time ago not all gauges are correct, they do fail. Granted this electronic stuff probable goes bad PV rather than drifting.
 

2kDoo

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Personally I don't agree.
If temp is reading too low could it not be a bad thermocouple? So when you hit 200 you could be 250...300 who knows. I've learned a long time ago not all gauges are correct, they do fail. Granted this electronic stuff probable goes bad PV rather than drifting.

Now that I drive an 05 lly I can say with 100% confidence your tranny is fine
Mine never gets over 130 in the week or so I had it and I def beat the snot out of it
Had to get a duramax cause 96 ram got stolen.
 
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