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Topic: Transmission temperature question
Posted By: EnzoColorado on 07/27/17 10:28pm

We just came back from a week of camping, driving from Colorado Springs to Ridgway State Park near Ouray and back. We drove Hwy 50 over Monarch Pass. This was our first time going over a truly high mountain pass. In the past we have gone over Le Veda and Wilkerson Pass and I never saw transmission temperature over 205. This trip, going west bound in 2nd gear at 40 to 45 MPH, the transmission temperature got to 232 at top of the Monarch Pass. We then stopped to ride the cable car up to the pass summit to see the view and also let the tranny cool down since I don't know if that's too hot or not. Coming back home today east bound on Monarch Pass, I was slower, between 2nd and 1st gear, and the tranny still got to 225 at the summit.

I do have an after market tranny cooler installed last year. This is towing pretty close to GCWR of my Suburban.

I never saw any warning light. However when I stopped at summit (to ride the cable car), I did smell a bit of burning outside of the Suburban.

Usually cruising rolling hills towing the TT, it doesn't get above 190 much.

So what's too hot? Is 232 causing damages?

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2012 Suburban 2500 LT 4WD

Posted By: Old-Biscuit on 07/27/17 10:51pm

High temp alarm S/B 250*F

Tranny really have to work hard on those mtn. passes especially when total load is at GCVWR

High sustained temps never good.


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Posted By: theoldwizard1 on 07/27/17 11:08pm

That chart is ancient history !

I worked in transmission engineering for one of the Big 3 back in the 80s. Even THEN, sustained temps under 230F were hot, but did not cause fluid or component failure.

Today, almost ALL transmission fluid is synthetic or synthetic blend and can comfortably handle 250F. Under 200F is ridiculous because most transmission coolers are inside the radiator and the engine coolant temperature is typically over 200F !

Don't get me wrong. Yes, you should check your transmission fluid regularly, more often if you are towing or carrying heavy loads. If it smells burnt or is NOT bright cherry red, it is time for a change. And use the EXACT fluid recommended by the manufacturer, Skip the "boutique" stuff !


Sure, keep it cool is the best policy, but lets be realistic !!

Posted By: lawrosa on 07/28/17 12:52am

theoldwizard1 wrote:

That chart is ancient history !

I worked in transmission engineering for one of the Big 3 back in the 80s. Even THEN, sustained temps under 230F were hot, but did not cause fluid or component failure.

Today, almost ALL transmission fluid is synthetic or synthetic blend and can comfortably handle 250F. Under 200F is ridiculous because most transmission coolers are inside the radiator and the engine coolant temperature is typically over 200F !

Don't get me wrong. Yes, you should check your transmission fluid regularly, more often if you are towing or carrying heavy loads. If it smells burnt or is NOT bright cherry red, it is time for a change. And use the EXACT fluid recommended by the manufacturer, Skip the "boutique" stuff !


Sure, keep it cool is the best policy, but lets be realistic !!


IDK. I added a large trans cooler in series with the stock GM cooler.

If I sit and idle with the silveradi the trans temp will match the coolant temp of 190f - 200f.

But driving to florida ( was 100 F outside most days) I crused at 160f trans temps and 190- 200f coolant temps.

Here is screen shot. This was in GA getting into florida crusing 75 mph at 11500 lbs.

[image]

Going in the smoky moantains the truck got hotter then the trans did. I think the truck got around 230-240f pulling grade to 5000ft and the trans never went over 190f.

Heres a vid pulling mountain grade. 1st gear 3500 RPM 30 MPH.

trans 175f
Coolant 230f

https://www.flickr.com/photos/93289479@N04/shares/GvSNN4

And trans cooler I moved factory unit down below the bowtie emblem

Put the biggest I could fit next to it.

Good thing is with A/C on the cooling fans run. I dont think we had the A/C off the whole trip..

I belive over 200F for a trans is too hot.

[image]

[image]

* This post was edited 07/28/17 01:08am by lawrosa *

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Posted By: NHIrish on 07/28/17 06:26am

I agree that the chart is certainly outdated, but heat is the enemy. Blanket statements seem to be a thing of the past with full synthetic fluids.

Electric cooling fans in my new Ford Powerstroke don't turn on until about 230. Normal operating temps on highway (not towing) are just under 200 for transmission and about the same for engine oil. Normal temps this high are new to me. Reports of 230 going over mountain passes are about average....at least for the Powerstroke. Further, even at those temps, the Ford 6 speed diesel engine transmissions HAVE NO DRAIN AND FILL REQUIREMENT UNTIL 150,000 miles, even under severe duty. Heat seems to be factored in.

Having said that, I was always amazed at how cool my 2011 Duramax Allison Transmission ran. Never saw 200 even over high mountain passes.

For the op, it is going to depend on the cooling scheme and fluids used by your manufacturer. Lots of different normals out there now.

* This post was edited 07/28/17 06:40am by NHIrish *

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Posted By: RinconVTR on 07/28/17 06:52am

None of those chart relate to modern ATF and Transmissions.

235...not much worry. None at all if its not a sustained temp.

I've had Honda's hit 240 while towing for very brief periods and that's exiting the trans. Which is important to know, because ATF temps are suppose to be measured after the cooler or near the sump. So while some may see a 240 reading, they may not know where that reading is derived from making their concern unwarranted.

Also note, Toyota Tundras and Sequoia's have a thermostat that keeps ATF around 200 at all times. Only recently did I find an app that will monitor highs and lows as the add in temp monitor I had in my Honda. And in all the towing I did in recently in day time temps reaching 121, the ATF temp gauge never budged. It appears automotive engineers might know what their doing.

Posted By: DustyR on 07/28/17 09:23am

I was told the transmission temp should be within 100* over the ambient temp. I don't know how reliable that is. IMHO

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Posted By: TurnThePage on 07/28/17 10:35am

The transmission temp in my last truck regularly climbed to just over 250F during long climbs. I was initially worried but there was never any detectable harm.

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Posted By: DiskDoctr on 07/28/17 10:39am

Recently it was confirmed by a very reliable source that the Ford 4R100 transmissions used in many of the older SuperDutys were good for 250F for 30 mins.

If hotter, give it a break and let it idle while stopped, preferably fast idle, until it cools down.

With the 6.0 cooler upgrade to my 7.3L Excursion, even when pushing a lot for extended periods, I never saw 200F.

Hope this helps.

Posted By: Dennis12 on 07/28/17 10:42am

Pic looks more like one of them air stills than a transmission cooler. Where ya live.

Dennis Hoppert

Posted By: Sandia Man on 07/28/17 10:50am

Being that we live and do most of our RVing in the four corner states we have hit those temps as well on occasion. Mentioned it to our mechanic at least a couple of times in the past and he didn't even blink, just said it was typical under extreme duty and synthetic transmission fluid could handle it. As a precaution I have a total tranny fluid flush every 25K miles although the last time we did it our mechanic said our tranny fluid was pink and still had plenty of life.

Posted By: EnzoColorado on 07/28/17 11:11am

Okay so sounds like the temperature I hit should be okay, especially since it was only over 15 minutes or so during the trip. Thanks everyone!

Posted By: BurbMan on 07/28/17 11:50am

The 2500 Sub comes stock with an external cooler in series with the one in the radiator. Trans typically runs at 175, unless stuck in traffic with the trailer in which case it will go to 200, but then drops again once traffic is moving and airflow is restored. Always runs cooler than the engine coolant.

In fact the stock trans never went over 200* right up until it failed at 140k miles LOL

Posted By: 1stgenfarmboy on 07/28/17 02:09pm

And remember the temp your sensor is reading is after it has been through all the coolers and is back in the pan, or at least mine is.


I had my sensor in the hot line at first and it scared the **** out of me.


If anyone is worried about there temps I would add another cooler, this is what I did, right now I am on a new performance built trans and extreemly high dollar converter, so I feel good about mine right now.


I would rather have a manual though.

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Posted By: hotpepperkid on 07/28/17 02:29pm

I start to get nervous when my temp gets over 200. I have a 2000 F-350 PSD and for what ever reason Ford didn't use oil to water but only oil to air cooler. It is fine as long as you don't do a lot of in town light to light driving on warm days, but when outside temps are 110 or so things head up really fast. I put the tranny cooler for the 6.0 on mine and oh WOW what a difference. Now light to light in town it gets up to 150 or so. I have tranny flushed every year just before towing season

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Posted By: tragusa3 on 07/28/17 02:46pm

I just did that same pass a month ago...got up to 232. There's only been 3-4 times that it ever got to those temps, and it was long, serious grades.

For those worried about 200 degrees...my truck will sometimes go to 204 on a grade with NO trailer.

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Posted By: Turtle n Peeps on 07/28/17 03:49pm

The chart listed is about as relevant today as the points setting on a 2017 engine.

Modern ATF can handle 275 F for short periods of time just fine.

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Posted By: steve-n-vicki on 07/29/17 04:43pm

Factory cooler ,with trailer tow package


[image]

Posted By: Hybridhunter on 07/30/17 05:01pm

230's is normal for that kind of towing, good idea to idle it before shutdown though. And change the fluid on schedule.

Posted By: joshuajim on 07/31/17 08:34am

Most vehicles these days run the trans fluid through the "air" cooler first and then through the radiator cooler. In this case, the air cooler might drop the temperature below radiator temp, but the radiator re-heats it. This is done for a reason that in the winter, the air cooler can overcool the fluid and that can be just as harmful to the trans as high temps.

Check your cooler line routing to see if this is the case. If so, the trans temp will run close to radiator temp.

RVing since 1995.

Posted By: RinconVTR on 07/31/17 08:39am

joshuajim wrote:

Most vehicles these days run the trans fluid through the "air" cooler first and then through the radiator cooler.


What make and model routes ATF thru an external ATF cooler first?

Posted By: BenK on 07/31/17 11:50am

This is a technology/science/laws of physics based discussion...

Yes, the often posted chart showing ATF temps vs what happens is old, but the basic premise is the same...just that the material science is MUCH better today than back then...but the metrics are still the same...just high temp ranges for the new materials

Yes, today's ATF can survive higher temps than the old stuff...but...it still has a temp specification that has working temp ranges (min to highest). Again, material science is much better and today's stuff has a higher working temp range

The "smell test" and "color test" still applies and again, at higher temps does these effects take place...never the less...they still smell burnt when it is burnt and turns color when it is burnt...meaning the ATF has gone BEYOND it's rated max temp

I know of no automatic tranny that has a thermal couple or whatever temp measuring component that measures where ATF gets burnt...at the tips/edges (both leading and trailing edges) of the TC vanes

Below pictures show the 'vanes' of the three components am talking about: Turbine, stator and impeller. All have vanes that throws ATF into/against the other's vanes. A reversal of fluid direction is where the main 'torque multiplication' comes from...other is the amount of slip (stall RPM). AKA fluid coupling...the why of removing that fluid coupling via lock up.

I can burn up anyone's TC/AFT in short order. Just give it high/full throttle and hold the brakes all the while at stall RPMs without lock up

[image]

[image]


"good for a while" at those gauge indicated temps is NOT the true temp of the ATF at the source/generation of heat (those tips & edges), but somewhere else in the tranny assembly. That has been muted (diluted) with colder ATF

The why of the age old and still good to this day..."the smell teste" and "the color test"...it is burnt beyond the 'extra' charge of ATF to dilute it and the filters ability to filter the burnt particles out of the flow

So, suggest each individual decide at which indicated temp they will run at pulling hard and decide on your flush regime

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