Atf breakdown temp

Joined
Jun 28, 2014
Messages
236
Location
In the field
I've done some research and it seems that atf starts to breakdown above 175f. True?? My 3.6 pentastar tranny runs at 190-197 consistently. Seems like these temps would affect the fluid rather quickly.
 
Joined
Apr 13, 2013
Messages
8,009
Location
FL, USA
I have heard the same thing. Not sure how much truth there is, todays fluids should be more resistant to break down. Just change it out a bit early each time.
 

MolaKule

Staff member
Joined
Jun 5, 2002
Messages
22,363
Location
Iowegia - USA
From a test I did for a Paper:
Quote:
A 'spirited' down shift on a hill at 55 mph, with no towing load, the ATF bulk temp went from 185F to 230F in 4.0 seconds and then went back down to about 190F 12 seconds later, a total time of 16 seconds.
This data was taken using a Nissan PathFinder with a four-speed (step-shift) Jasco and a 3.5L engine. For a beginning Sump temperature of 175F, the clutchpack (not the bulk fluid) will easily reach 335F at 0.5 sec. after engagement and then cool down rather quickly.
Quote:
High fluid temperatures oxidizes fluid. Oxidation alters the Friction Modifier, causes sludging, degrades Anti-Wear (AW) agent, and degrades seals. High fluid temperatures varnishes clutch discs, plates, bands, valves and actuators. Varnishing of clutch discs severely modifies clutch disc material surface friction coefficients ui and u0.
While there may be temperature spikes, I doubt the bulk (sump) temperature ever remains high enough to seriously degrade the fluid in normal driving. With today's advanced fluids and additive packages, oxidation and degradation is not as serious as in past years. When does a fluid begin to degrade? The first time the engine fires. If you plot oxidation percentages verses temperatures, then a sump temp of 300F will certainly degrade fluid faster than having an average sump temperature of 185F. So fluid oxidation is highly dependent on how long ( or dwell time) the fluid is at the elevated temperature.
 
Last edited:
Joined
Apr 8, 2013
Messages
3,506
Location
Delaware
I remember reading somewhere the breakdown temperature for Dexron-VI was somewhere around 270F. Modern day ATF's can handle very high temperatures.
 
Joined
Dec 12, 2002
Messages
43,672
Location
'Stralia
There's a "rule of thumb" that industrial oils degrade twice as fast every 10C(18F) over 80C(175F) oil temperatures. An oil that's good for 20,000 hours at 80C, is good for 10,000 hours at 90C, and 5,000 hours at 100C.
 
Joined
Apr 9, 2008
Messages
15,201
Location
Central NY
Originally Posted By: MolaKule
From a test I did for a Paper:
Quote:
A 'spirited' down shift on a hill at 55 mph, with no towing load, the ATF bulk temp went from 185F to 230F in 4.0 seconds and then went back down to about 190F 12 seconds later, a total time of 16 seconds.
This data was taken using a Nissan PathFinder with a four-speed (step-shift) Jasco and a 3.5L engine. For a beginning Sump temperature of 175F, the clutchpack (not the bulk fluid) will easily reach 335F at 0.5 sec. after engagement and then cool down rather quickly.
Quote:
High fluid temperatures oxidizes fluid. Oxidation alters the Friction Modifier, causes sludging, degrades Anti-Wear (AW) agent, and degrades seals. High fluid temperatures varnishes clutch discs, plates, bands, valves and actuators. Varnishing of clutch discs severely modifies clutch disc material surface friction coefficients ui and u0.
While there may be temperature spikes, I doubt the bulk (sump) temperature ever remains high enough to seriously degrade the fluid in normal driving. With today's advanced fluids and additive packages, oxidation and degradation is not as serious as in past years. When does a fluid begin to degrade? The first time the engine fires. If you plot oxidation percentages verses temperatures, then a sump temp of 300F will certainly degrade fluid faster than having an average sump temperature of 185F. So fluid oxidation is highly dependent on how long ( or dwell time) the fluid is at the elevated temperature.
I thought I read somewhere that those Pathfinders have higher trans temps because the exhaust crossover pipe runs directly under the transmission pan ... and it tends to cook the transmission.
 
Joined
Nov 9, 2008
Messages
18,716
Location
NH
A lot of info on the web comes from decades ago. While the drop in oil life may well be halved for every 10C / 10F rise, casual reading would make one think imminent transmission death if sump temp was at 180F, let alone 200F, for any amount of time. I know I was fooled by the amount of wisdom arising from old school automatics where people were aiming to go no higher than 180F while towing--and mine was running at 190-200 while doing nothing!
 

MolaKule

Staff member
Joined
Jun 5, 2002
Messages
22,363
Location
Iowegia - USA
Originally Posted By: Miller88
I thought I read somewhere that those Pathfinders have higher trans temps because the exhaust crossover pipe runs directly under the transmission pan ... and it tends to cook the transmission.
Mine is a 2003 and there is no crossover pipe running under the tranny. Mine has over 150,000 miles on it and is one of my test mules for devopment fluids and shifts like it did when new.
 
Last edited:
Joined
Oct 10, 2008
Messages
19,699
Location
Sunny Florida
Originally Posted By: Nate1979
I remember reading somewhere the breakdown temperature for Dexron-VI was somewhere around 270F. Modern day ATF's can handle very high temperatures.
All of our fleet trucks run the trans fluid right into the radiator, with a factory thermostat at 205 degrees. My new Ram has coolant delivered directly to a heat exchanger on the side of the ZF 8 speed, and per them it is as much to warm the fluid as to cool it. Modern ATF fluids are not harmed at normal temps like older fluids. The same goes for modern oils...
 
Joined
Feb 20, 2007
Messages
5,381
Location
Southeast
after 45 minutes, the trans in our T&C is always ~180-190 if the A/C is on. If it's off, it varies wildly with the season. 180-190 summer, 120 winter. Summer with the air on, 210 normal plus spikes is about what I see. They seem to run hotter than the average. The tundra rarely sees 130 on daily commute, and rarely climbs over 160F when towing. <-- that's sump. converter temp regularly jumps 20+ over sump and settles back down.
 
Top