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#502819 - 10/10/03 07:37 AM How hot is transmission fluid supposed to get?
Chris B. Offline


Registered: 03/16/03
Posts: 2915
Loc: Colorado
I was just wondering how hot a transmission on a car or truck will get normally? What temps do most car and trucks transmission fluid see from everyday driving?
I was checking my 2003 Silverado and after a run on the highway for about 20 minutes. The fluid was hot but not as hot as the engine oil. Is the transmission fluid supposed to get hot enough to burn you to the touch like engine oil can? I was just wondering because I know you are supposed to check it when it is "hot" but how hot is hot enough?
Mine was low so I added a qt or so and it brought it up to a tad over the fill line on the dip stick but every time I check it it is eithor a hair low or high. How much over can the transmission be filled before it causes damage to it? Thank you for the help!

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#502820 - 10/10/03 09:33 AM Re: How hot is transmission fluid supposed to get?
JohnBrowning Offline


Registered: 05/01/03
Posts: 9448
Loc: USA
It should never get hotter then 233F. I was reviewing an SAE paper. GM was testing in the desert with a towing dyno hooked to a fullsize C/K truck. The load ranged from 1500-5500. THe grades also varied and the speed started at 20MPH and went to 60MPH. They graphed trany fluid temps and all other reported parameters from PCM and independent data recording systems under all grades, speeds and loads. THe basline used OEM trany fluid and the transmission recorded temps far in excess of the 233F limit.

Then the same tests were repeated under the same conditions. THe second time around the tranny fluid was heavily ester based. THe second time around the temp never exceeded 213F!

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#502821 - 10/10/03 09:50 AM Re: How hot is transmission fluid supposed to get?
wulimaster Offline


Registered: 02/07/03
Posts: 1011
Loc: Montgomery, Alabama
quote:
Originally posted by JohnBrowning:
It should never get hotter then 233F. I was reviewing an SAE paper. GM was testing in the desert with a towing dyno hooked to a fullsize C/K truck. The load ranged from 1500-5500. THe grades also varied and the speed started at 20MPH and went to 60MPH. They graphed trany fluid temps and all other reported parameters from PCM and independent data recording systems under all grades, speeds and loads. THe basline used OEM trany fluid and the transmission recorded temps far in excess of the 233F limit.

Then the same tests were repeated under the same conditions. THe second time around the tranny fluid was heavily ester based. THe second time around the temp never exceeded 213F!

This is why I run synthetic in my trannys. Keeps them cooler without having to add an external cooler and they have a 100 degree F higher limit on them before degradation sets in.

Synthetic ATF works equally well in power steering units that call for ATF.

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#502822 - 10/10/03 07:10 PM Re: How hot is transmission fluid supposed to get?
JohnBrowning Offline


Registered: 05/01/03
Posts: 9448
Loc: USA
Wulimaster I wish I had some way to copy these documents at work to bring here. THe temp chart with OEM looked like the Andes mountains and went way past the temp limit set for the proper operation of this trans. THe next chart was very gradual and did not exhibit that much variation from on end of the chart to the other and it never exceeded safe temps.

To restate that one looked like a very jaged triangle while the other one looked like the shape of the average womens bicep with a gentle curve from oend to end.

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#502823 - 10/10/03 11:25 PM Re: How hot is transmission fluid supposed to get?
Cutehumor Offline


Registered: 12/10/02
Posts: 8994
Loc: USA
[/qb][/QUOTE]This is why I run synthetic in my trannys. Keeps them cooler without having to add an external cooler and they have a 100 degree F higher limit on them before degradation sets in.

Synthetic ATF works equally well in power steering units that call for ATF. [/QB][/QUOTE]

there is a guy on the edmunds board by the name of mr. shiftright that argued that transmission coolers were necessary to transfer the heat away from the tranny oil regardless of synthetic or not. when tranny temps exceed normal ranges, he said something about if the synthetic oil withstands the excess heat, can the internal parts of the tranny withstand the heat also?

btw, I'm runnin redline d4 atf in the tranny with tranny cooler. [Cheers!]

[ October 11, 2003, 02:28 PM: Message edited by: Cutehumor ]

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#502824 - 10/12/03 10:19 PM Re: How hot is transmission fluid supposed to get?
Jimbo Offline


Registered: 02/13/03
Posts: 1347
Loc: California, USA
There was another GM paper that pretty much stated that once the oil temperature hits 300F, all of the "soft" (non-metallic) parts of the transmission are destroyed within a short time.

Since I thought most of the heat came from the torque converter doing its job, how would ester-based fluid not heat up just as much? Do esters have lower surface tension and better heat transfer in the cooler?

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#502825 - 10/13/03 10:02 PM Re: How hot is transmission fluid supposed to get?
Ray H Offline


Registered: 01/16/03
Posts: 4478
Loc: Southern California
I'm presuming that "soft" refers to adhesives holding the fibrous clutch facing material together as well as various delrin, nylon, teflon, etc. plastics and electrical insulating materials used in solonoids. 300 degress F. can be "merely" thermally deadly to these substances (softening or dissolving), as well as promoting oxidation to the hydrocarbon content of the fluid, itself. This is literally frying temperature!

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#502826 - 10/13/03 10:47 PM Re: How hot is transmission fluid supposed to get?
Chris B. Offline


Registered: 03/16/03
Posts: 2915
Loc: Colorado
Did a 300 mile trip on the highway doing 80mph and the transmission fluid was not very hot just felt like warm water.

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#502827 - 10/14/03 01:28 AM Re: How hot is transmission fluid supposed to get?
jeepzj Offline


Registered: 08/23/02
Posts: 377
Loc: New Jersey, USA
quote:
Originally posted by Chris B.:
Did a 300 mile trip on the highway doing 80mph and the transmission fluid was not very hot just felt like warm water.

Transmission fluid gets hotter in city stop-and- go traffic and towing. Driving on the highway cruising at 80MPH in 5th gear overdrive is much better for the tranny and keeps it cooler.
City driving and towing is severe duty so that's why the fluid should be changed more frequently. What brand of ATF are you using by the way?

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#502828 - 10/14/03 06:29 AM Re: How hot is transmission fluid supposed to get?
Chris B. Offline


Registered: 03/16/03
Posts: 2915
Loc: Colorado
It has the factory fill in it at 9,500 miles and I toped it off with Ammoco Transmission fluid dexron III.

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#502829 - 10/14/03 07:28 AM Re: How hot is transmission fluid supposed to get?
Rick in PA Offline


Registered: 01/04/03
Posts: 2202
Loc: Southeastern, PA
[Off Topic!]
My brother plows snow in the winter and had this story. A guy was plowing snow with a fairly new truck. Plowing snow puts a lot of load on the transmission. The transmission fluid overheated and softened the main seal. When the main seal blew, it sprayed transmission fluid on the torque converter which slung it everywhere. The transmission fluid got on the red-hot exhaust pipe. The transmission fluid ignited and started burning vigorously. The truck caught fire and was a total loss, 100% burnt.

Moral: if you're plowing snow with an auto tranny, get a temperature gauge for the transmission fluid and keep an eye on it.

[ October 14, 2003, 10:29 PM: Message edited by: Rick in PA ]

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#502830 - 10/15/03 12:29 AM Re: How hot is transmission fluid supposed to get?
Ray H Offline


Registered: 01/16/03
Posts: 4478
Loc: Southern California
quote:
Originally posted by Chris B.:
It has the factory fill in it at 9,500 miles and I toped it off with Ammoco Transmission fluid dexron III.

Nope, deleted. Blotto. I mis-read "Ammoco" as "Aamco".

[ October 15, 2003, 03:33 PM: Message edited by: Ray H ]

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#502831 - 10/15/03 12:48 AM Re: How hot is transmission fluid supposed to get?
V6 Diesel Offline


Registered: 10/27/02
Posts: 144
Loc: Michigan, outside Lansing
Years ago I had a 76 Chevy 4x4 that I installed a temp gauge for the tranny fluid. The sensor was mounted in the tranny pan. I was running a large tranny cooler but don't know where the temps were at before the cooler was installed.

During off-roading/dunes the temp went up to 180 degrees the hottest. Highway driving about 160 was the hottest. What would drive the temps up quickly was moving a travel trailer around, backing it back and forth moving it around. Likely the heavy work with out much air movement over the cooler was part of it.

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#502832 - 08/19/04 11:04 PM Re: How hot is transmission fluid supposed to get?
jason07-1zzfe Offline


Registered: 06/10/02
Posts: 2095
Loc: IL
John is that temp accurate? That is scary because I just got a scan tool recently and the tranny temp even after being babied was 220F and after I drove it for a bit romping on it a little was up to 280F. This is in only 60F ambient! On a 2001 GTP.
No wonder I have crazy wear metals when I drop the pan!
Also pertaining to your info...I am at pretty much 100% RL D4 ATF now. 3 changeouts with over 70% new fluid with each drain.
I can't imagine my tranny temps if I didn't have RL if that is really true. OTherwise the difference really isn't that drastic.
I think I need a tranny cooler!!

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#502833 - 08/20/04 06:29 AM Re: How hot is transmission fluid supposed to get?
DJ Offline


Registered: 01/12/04
Posts: 738
Loc: New London WI
quote:
Originally posted by Rick in PA:
[Off Topic!]
My brother plows snow in the winter and had this story. A guy was plowing snow with a fairly new truck. Plowing snow puts a lot of load on the transmission. The transmission fluid overheated and softened the main seal. When the main seal blew, it sprayed transmission fluid on the torque converter which slung it everywhere. The transmission fluid got on the red-hot exhaust pipe. The transmission fluid ignited and started burning vigorously. The truck caught fire and was a total loss, 100% burnt.

Moral: if you're plowing snow with an auto tranny, get a temperature gauge for the transmission fluid and keep an eye on it.

We had a similar thing happen to an employers plow truck, only we put the fire out fast. Didn't know why it lit up, upon rewiring the shop said it started at the exhaust manifold, they did not know what burned till they went to back it out of the gagage and the tranny was shot, the fuid had blown out the dipstick. With the new tranny they put in a temp gauge.

Jason, those temps should be death for the tranny, I suggest trying the scanner on another similar car and maybe a different scanner on your car just to verify that miscommunication between those are not the problems. Then if need be correct the problem fast. I had M1 in my tranny and it hit 250-60 as seen by the pcm and that cooked the fluid in minutes was black when I got home, there was an internal problem got that corrected and the fluid changed tranny lasted another month and died alltogether.

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