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how hot is too hot for auto transmission fluid?

blakes

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My GF has a 2004 Toyota Matrix with auto tranny and 220k miles. Tranny fluid looks and smells ok. It runs and shifts fine.

Our drive home from town consists of about 20 miles of a canyon highway mostly uphill and then about 6 miles of fairly steep dirt road. The Torque app shows the tranny fluid gets to about 250 degrees by the time we make it all the way up the mountain. If we are driving around town the fluid stays at about 150 degrees or so. The tranny cooler is in the radiator and the electric fan works fine. The coolant temp gets to about 210 or so.

Is 250 degree Fahrenheit too hot for ATF?
 

Arps

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The ideal operating temperature of transmission fluid is 175 degrees. Overheating occurs after the temperature surpasses 200 degrees, and the failure rate doubles for every additional 20 degree increase after that.

from google
 

45acp

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250 is fucking super hot and the fluid is probably roached. Maybe not, but a home done flush is alot cheaper than a rebuild months/year(s) from now.
 

87manche

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I generally shoot for 180ish

warm enough to evaporate moisture and reach full viscosity.
not hot enough to kill it.

250 is kills it temps.
 

gunracer1

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my old motor home saw 275 towing from durango to silverton. and it was 40 degrees out. i sold it 5000 miles later. i was impressed with that turbo 400.
 

j20brett

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Fun fact, ford's 6r80 trans has a thermostat built in that doesnt open til trans hits 190. My '13 f150 ecoboost generally sees 205 to 215 towing my jeep/camper in hills from tx to pa to ut. Just changed/flushed the fluid for the 3rd time at 189k miles.
 

Wulf

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Fun fact, ford's 6r80 trans has a thermostat built in that doesnt open til trans hits 190. My '13 f150 ecoboost generally sees 205 to 215 towing my jeep/camper in hills from tx to pa to ut. Just changed/flushed the fluid for the 3rd time at 189k miles.


Yeah, I'm not sure the temps posted above are accurate for modern fluids/transmissions. My 2016 350 trans runs at 200 unloaded and will get up to 215+ towing. Fluid is not burnt but due for a change.
 

yozsi

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I always like to see below 230 degrees on atf temps. I've noticed a big drop in temps ~15-30 degrees when i replace shitty atf with tractor hydraulic oil. ATF really loses its ability to lubricate at higher temps i think mainly due to its low viscosity.
 

CarterKraft

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The ideal operating temperature of transmission fluid is 175 degrees. Overheating occurs after the temperature surpasses 200 degrees, and the failure rate doubles for every additional 20 degree increase after that.

from google

Definitely not accurate. 6R140 trans in Superduty's runs 200F all day but don't go much over 215F towing heavy.

I am thinking your converter is unlocking causing the heating, watch that PID in Torque to see if it is being told to unlock or if its slipping.
 

not2hye

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Definitely not accurate. 6R140 trans in Superduty's runs 200F all day but don't go much over 215F towing heavy.

I am thinking your converter is unlocking causing the heating, watch that PID in Torque to see if it is being told to unlock or if its slipping.

Ive read a lot of complaints about the 6r140 running on the warm side. My ‘12 has never had a hot trans temp issue. Even buggy whipping that thing up the hills with a toyhauler behind it. Engine oil temp is a different story.

i believe there is a thermostat delete or colder kit you can buy aftermarket. Another company is selling an air to oil cooler for them that’s supposed to work pretty good. I can’t think of the names off the top of my head.
 

CarterKraft

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Ive read a lot of complaints about the 6r140 running on the warm side. My ‘12 has never had a hot trans temp issue. Even buggy whipping that thing up the hills with a toyhauler behind it. Engine oil temp is a different story.

i believe there is a thermostat delete or colder kit you can buy aftermarket. Another company is selling an air to oil cooler for them that’s supposed to work pretty good. I can’t think of the names off the top of my head.

I think they are complaints from people used to 4R100 temps as a 200+ temp on my 4r100 would have scared me.
In the heavy equipment world 200 would be operating temp, not scared.
 

SLOWPOKE693

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my 2019 F550 service truck has run between 200 and 215 since the day it was new. Transmission fluid still looks and smells fine. Its currently got 46k miles on it.

Truck rolls down the road at 18,760lbs.
 

D Nelly

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If you're regularly hitting 250 but the fluid on the stick looks and smells normal I'd question the sender/gauge a little
 

Tiha

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Here's a thought.

Where is the temperature taken? Pre or post cooler?

Would it matter where it was taken?


Maybe post cooler temps are 170, is that okay even if pre cooler temps are 250?

The converter creates the most heat and typically flow is from the converter to the cooler and then the rest of the trans.


I do know that trans heat is enormous with the converter unlocked. If you can select a lower gear for those canyon drives and still get the converter to lockup that would be best.

This is what killed the 700R4 behind the diesels, The converter would lock up in 2nd gear if the rpms were up high enough. But people lugged it in third never locking the converter and melting the trans.

Awesome that you are watching the temp, now you need to find out if there is a certain way to drive to prevent meltdown. The engineers may well have built something in.

Some transmissions for a while had a temp sensor as a safety to lock up the converter and cool it down, the ones I remember were set at 240 degrees.
 

rockdog57

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Too cold can do damage as well. Talked with John Wood about my 4r100 he was doing for me. He said don’t flog it before it has a chance to warm up a little in the winter. I put a six slow cooler in front of it and the thing hardly ever goes above 160 when towing. I think I’d be putting an external cooler on it pronto. It won’t live long with 250 temps! It
 

bdkw1

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Run a good synthetic oil and 250 isn't an issue. If you want to get a good scare going, put a sensor on the output from the converter. Not uncommon to see 300+ coming out of it.
 

92 s dime

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Drop down a gear or turn off OD and use torque to monitor the converter slip
with my towncar in the mountains the trans will stay in OD but slip the converter,turn off OD and the converter stays locked up and the fluid temps stay around 170f
 
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