Tranny temps: how hot is too hot?

My 4L80E was destroyed due to a corrosion issue inside the engine PCU. Always check for any type of issue outside the actual transmission.

On my previous 2007 Ram/Cummins, the TRANS TEMP warning light was calibrated to come on at 260*F. I had it up to 250*F before with no warning light. So the manufacturer thinks anything over 260*F is definitely a problem, and I agree.

I think something that is important to remember is the duration of those temps. 250*F while climbing a short grade (a few minutes or less) vs. all day long is quite a different issue. I wouldn't want to run a trans to 250 all day, but a short spike to 250 while climbing a hill is no big deal.

I like to see mine under 210*F sustained, 250*F for very short periods.

smkettner wrote:

marcsbigfoot20b27 wrote:
Well I am a sucker for information. Please do show some evidence of how hot is safe for regular and synthetic fluids and the seals in the transmissions. I would love to know the real answer.
Remember that not all of us tow with a 2015, some of us are still old school ~1995-2005

The thread is primarily about the OP's truck: "I will be towing with my 2011 Silverado 1500 LTZ".

This is what the 'newer truck' answers are talking about.

I hear ha.

I'm just waiting for some real answers on how much more heat the newer transmissions can supposedly handle. I don't see any info on the web, but I would love to know the truth.

marcsbigfoot20b27 wrote:
Well I am a sucker for information. Please do show some evidence of how hot is safe for regular and synthetic fluids and the seals in the transmissions. I would love to know the real answer.
Remember that not all of us tow with a 2015, some of us are still old school ~1995-2005

The thread is primarily about the OP's truck: "I will be towing with my 2011 Silverado 1500 LTZ".

This is what the 'newer truck' answers are talking about.

I have a very similar truck (2012 gmc). It's real hot here in central CA, I would see 200 on the flats at times. One of my tows is up a steep 12 mile grade, my transmission would hit 220 1/4 of the way up the hill. I would pull over let it cool 3-4 times before I hit the top. I'm sure it was fine but I didn't want to risk it.

I added an aftermarket cooler in line with the factory cooler. Now on that same Hill I won't even hit 200 at the top in 90-100 weather.

Just found out last week the temp parameter that kicks the engine fan on in my F-150 is 240 degrees.

Also found out, my problem isn't the engine fan. The only parameter of the four that's up causing the fan to come on is trans temp. Ouch!Gonna be spendy but can't complain too much at 120K miles at max capacity.

Forgot to touch on this...

Say the new ATF's are good for 270*F as most here are saying...

Anyone know what the duty cycle is for the OEM's 270*F max temp spec is?

If 100%, then it can run 100% of the time there at 270*F...if 40%, then it
can run at 270*F for 40% of the time with a cool down time...but...that
then needs how that OEM defines duty cycle.

Some times that 40% duty cycle will NOT have the spec say 60% time to cool
down...but an actual lower temp it must attain before going back up there in temp

This type of thing(s) are not 'snap' transitions

Meaning that once it reaches the max temp of the temp range specified...will
it fail instantly...or that if it is just a hair underneath that line...that
there is no degradation

The closer it gets...the longer it dwells at those elevated temps...the more
degradation of the ATF or any fluids with a temp range (min to max) specification

What fails...are two main components in this food chain...the AFT and
the seals/materials/friction material/etc inside the automatic tranny

This can also add heat load to the engine thermal management system
to cause it to work harder

Know that all or most all things in the computer systems (yes
plural) have temp limits that then cause them (computer systems)
to go into the various limp modes...until total shut down mode...

marcsbigfoot20b27 wrote:
Yep, its not just about the fluid.......its also how much heat the seals can handle. One seal failure can mean totally disabled trans.

I worked at a transmission shop for 4 years (23 years ago) Seen lots of burned up units, some with wasted seals and clutch packs where the glue that holds the fiber to the steel was gone.

Anything over 225 for more than 5 minutes and I would pull over or add a bigger cooler. It doesn't matter if you have full synthetic that can handle 350 degrees if the seals melt.

My truck stock would get up to 210 going up the rim in AZ. Added a way bigger cooler and now it only gets to 160 max ever.

I agree if you are driving a 20+ year old truck. The newer units are designed to be able to run hotter (I agree cooler is better) than those 20+ years ago. I know that if I put Dextron VI in my 1973 Turbo 400 transmission that the fluid will handle higher temps but the transmission itself, not so much. Seals and clutches as you say are not built to take the heat that the newer transmissions are.

GM factory is saying the 2007 and up 6 speed (not talking about Allison) can handle more heat.

captnjack wrote:

marcsbigfoot20b27 wrote:

Turtle n Peeps wrote:

marcsbigfoot20b27 wrote:
Yep, its not just about the fluid.......its also how much heat the seals can handle. One seal failure can mean totally disabled trans.

I worked at a transmission shop for 4 years (23 years ago) Seen lots of burned up units, some with wasted seals and clutch packs where the glue that holds the fiber to the steel was gone.

Anything over 225 for more than 5 minutes and I would pull over or add a bigger cooler. It doesn't matter if you have full synthetic that can handle 350 degrees if the seals melt.

My truck stock would get up to 210 going up the rim in AZ. Added a way bigger cooler and now it only gets to 160 max ever.

Do you think seal technology has stood still for 30 or 40 years? Just like fluid and everything else, the technology has increased immensely.


Mark; where are you at? Time to straighten some of these people out. :B Your phone is ringing!!

Well I am a sucker for information. Please do show some evidence of how hot is safe for regular and synthetic fluids and the seals in the transmissions. I would love to know the real answer.
Remember that not all of us tow with a 2015, some of us are still old school ~1995-2005

I posted earlier about my 2002 Chevy. 225 for five minutes is nowhere near to being a problem. From the owner's manual. That's good enough for me. Although 225 is around the number I look to stay under. Can't always hit that five minute mark though. I wait for top of hill, then pull over to cool down.

Yep, owners manual kinda answers the problem. Seems like 255* is the number I remember.

If 200* is 'hot,' I'm in trouble. My F150 is at 195-200* all the time (once it has time to warm up, of course)! Even in sub-freezing winter temps. Of course, towing, it stays in the same range, maybe creeping up to 205 or 210* on an extended climb.