When is an ATF too hot?

Status
Not open for further replies.
Joined
Jan 15, 2006
Messages
732
Location
Canada
I started on my transmission temperature gauge install last night - did all the wiring so that I can install both the sender and the gauge itself. Sender will be going on in a brass t-fitting I got (splicing into the "out" line of the transmission) once I do the ATF drain and fill (maybe tonight if I get a chance).

The transmission is an Aisin U151E, mated to a 3MZ-FE in a Toyota Sienna. The shop manual states the following, with respect to checking the fluid level:

"Drive the vehicle so that the engine and transaxle are at normal operating temperature.

Fluid temperature: 70 - 80 °C (158 - 176 °F)"


That's the "normal" range, but what is too hot that I need to worry about the ATF degrading too quickly leading to transmission failure. 177°F? 200°F? If say 180°F is in reality on the high side, but otherwise safe, I don't want to be panicking because it is over the 176°F.

Guessing the temperature ATF degrades rapidly at is pretty much the same across ATFs and transmissions.

Fluid used, btw is T-IV/JWS3309.
 
Yes around 220 to 230. It's very hot here and one of our most purchased items is larger or additional trans coolers. Optimal is 165 to 185 for longevity. many of my customers that pull large trailer see around 190 with aftermarket coolers and was close to 250 before the new cooler
 
Last edited:
Is that 220 measured at the line to the cooler as Weebl has it?

Or is it 220 in the pan...and how much do those values differ?
 
Last edited:
Hmmmm ... just got a new Ford F-150 and has the transmission cooler.. and the transmission temperature guage. I'm under 1,000 miles and mine always runs just a fuzz under 200 degrees without trailer.

???
 
Originally Posted By: Astro14
Is that 220 measured at the line to the cooler as Weebl has it?

Or is it 220 in the pan...and how much do those values differ?



We dont install guages in a cooler or line. Our guages go into a port in the side of the trans. Factory type guages are NEVER accurate. I see alot of people use scan guages ECT and swear by them but they pickup the exact signal the factory guages do.
Ford is notorious for having lieing guages. Im actually willing to bet the actual temp is lower then what the F150 is showing with no load.

We have replaced many of the V10 type coolers with Tru cool cooler and seen huge drops in temp. With syn fluid we have all customer on 50,000 mile servicing
 
Last edited:
I installed the auxiliary cooler in my 2003 echo with U340E transmission and noticed that normal operating temperature dropped from 175 F in the summer to 140 F - 150 F and never went above $160 F even when it was 105 F outside. In the winter it was running 100 - 110 F
 
Be prepared for wildly varying temps and high ones by measuring the cooler out line. That "normal" temp range you found is mostly likely bulk temp... measured in the pan. This is a lower and more temp stable area to measure trans temp than the cooler out line. Measuring the cooler out line, you will see temps climb and fall rapidly according to load and whether or not the converter is locked.

Overall, it's time at temp that counts, so the spikes will you see, maybe 225 or higher, have to be factored by knowing that the pan temp, where the the oil "dwells" the longest, is probably only 180.

I had gauges mounted on the pan, the cooler out line and also the return line back to the trans on one of my past vehicles. At times I saw 100+ degrees different at the cooler out line vs the pan, and where there was a lot of temp differential (cool ambient, hot trans) I saw 90 degree oil going back to a trans with 225 at the cooler out and 185 in the pan.

Currently, I can monitor pan and cooler out of my current Ford and when the converter is locked, the temps run at nearly identical levels. Put the truck to work towing grain wagons, as I recently did during wheat harvest, I saw 240 on the cooler out and 160 in the pan. Within a few minutes of the converter locking, temp dropping 50 degrees

I advise a lot of monitoring before jumping to any cooler or upgrade conclusions.
 
Last edited:
Originally Posted By: dkrivosheyev
I installed the auxiliary cooler in my 2003 echo with U340E transmission and noticed that normal operating temperature dropped from 175 F in the summer to 140 F - 150 F and never went above $160 F even when it was 105 F outside. In the winter it was running 100 - 110 F


But are those temperature ranges now considered too cold for optimal ATF performance or is there no such thing as too cold until one drops below say room temperature?
 
The sump is usually just a bit warmer than the cooler outlet.

What kills any oil is time at temperature. The longer the oil is at high temperature, the quicker it dies. The hot oil from the torque converter pumped through the cooler isn't hot for as long a time as the cooler oil flowing in the sump.
 
Originally Posted By: Jim Allen
Be prepared for wildly varying temps and high ones by measuring the cooler out line. That "normal" temp range you found is mostly likely bulk temp... measured in the pan. This is a lower and more temp stable area to measure trans temp than the cooler out line. Measuring the cooler out line, you will see temps climb and fall rapidly according to load and whether or not the converter is locked.

Overall, it's time at temp that counts, so the spikes will you see, maybe 225 or higher, have to be factored by knowing that the pan temp, where the the oil "dwells" the longest, is probably only 180.

I had gauges mounted on the pan, the cooler out line and also the return line back to the trans on one of my past vehicles. At times I saw 100+ degrees different at the cooler out line vs the pan, and where there was a lot of temp differential (cool ambient, hot trans) I saw 90 degree oil going back to a trans with 225 at the cooler out and 185 in the pan.

Currently, I can monitor pan and cooler out of my current Ford and when the converter is locked, the temps run at nearly identical levels. Put the truck to work towing grain wagons, as I recently did during wheat harvest, I saw 240 on the cooler out and 160 in the pan. Within a few minutes of the converter locking, temp dropping 50 degrees

I advise a lot of monitoring before jumping to any cooler or upgrade conclusions.


Thank you. Glad to know I can expect quite a bit of variability as I drive. Wouldn't I want to know what the peaks are? I realize that the pan temperature is more stable, but is knowing that it is spiking up to say 225 not of value in indicating I should consider additional cooling? In towing, I can usually feel and hear when the torque converter has unlocked, at which point, I immediately shift out of D on this 5 speed transmission, and into 4. I understand that this transmission can lock the converter in 3rd, 4th or 5th. A side benefit I see is when my wife is driving while towing, who may not hear or feel the torque converter unlock. She doesn't care to be mechanically inclined, but has driven manual transmissions and uses that frame of reference for shifting to a lower gear manually, rather than understanding that by going into 4, you are doing this to force the transmission from an "unlocked" 5 into a (hopefully) "locked" 4th. I can now hopefully use the gauge to advise her when it climbs above x, shift into 4.

I think I will try to log while I'm a passenger and not a driver the temperature under a variety of conditions, both towing and not.
 
Originally Posted By: weebl
Wouldn't I want to know what the peaks are?


Yes! I kinda liked to watch the cooler out temps because it was also a load indicator. The vehicle I described was primarily a four-wheeling machine and me being a certified gauge-o-haulic, I had to know everything that was going on. Leaned a lot from it, including what 300+ degree looked (and smelled) like as well as the dreaded "cherry volcano" when overheated ATF boils up out of the dipstick tube! Ah, yes, those were the days, my friend!

Mainly, I was just advising perspective. Watch the gauge and learn "normal." IMO, if or when you start seeing a lot of 220+ temps working your rig as you normally do, then you need to start thinking about cooling system upgrades. Occasional spikes are not too worrisome. To a certain point, high temps can be countered by simply shortening the OCI to account for the increased oxidation. It doesn't really hurt the trans to run at 250F but it oxidized the fluid much more quickly.If you change the fluid out before it's used up, no harm, no foul. If you start seeing a lot of 280-320F, that's when the temps, in and of themselves, can be harmful to the trans.
 
Last edited:
From my observations, the hottest place in the transmission is the Torque Converter, I have taken temps at the cooler lines as well as the trans pan, and my hottest temps via an Infrared Gun have come from the Torque Converter.
 
In a lot of cars, trans oil temp follows coolant temp pretty closely except under high load due to the combined cooling setups.

I don't think you want them to run too cool either...
 
Originally Posted By: Jim Allen
Yes! I kinda liked to watch the cooler out temps because it was also a load indicator. The vehicle I described was primarily a four-wheeling machine and me being a certified gauge-o-haulic, I had to know everything that was going on. Leaned a lot from it, including what 300+ degree looked (and smelled) like as well as the dreaded "cherry volcano" when overheated ATF boils up out of the dipstick tube! Ah, yes, those were the days, my friend!

Mainly, I was just advising perspective. Watch the gauge and learn "normal." IMO, if or when you start seeing a lot of 220+ temps working your rig as you normally do, then you need to start thinking about cooling system upgrades. Occasional spikes are not too worrisome. To a certain point, high temps can be countered by simply shortening the OCI to account for the increased oxidation. It doesn't really hurt the trans to run at 250F but it oxidized the fluid much more quickly.If you change the fluid out before it's used up, no harm, no foul. If you start seeing a lot of 280-320F, that's when the temps, in and of themselves, can be harmful to the trans.


Do you still go offroading? Definitely sounds like a lot of fun. Good chance once my son turns 16 ten years from now, he'll get himself a 4x4, and I'll be going with him. Would be a great father-son bonding experience.

I will definitely start seeing what's normal (no towing load) versus what I see towing, especially under acceleration or climbing hills. That will help me get a feel if I want to start changing out ATF more frequently or if I want a cooler. The cooler is still tempting just to add extra ATF, but at the same time, I don't want it to be overkill.
 
Originally Posted By: kballowe
Hmmmm ... just got a new Ford F-150 and has the transmission cooler.. and the transmission temperature guage. I'm under 1,000 miles and mine always runs just a fuzz under 200 degrees without trailer.

???



Your Ford like my GMC has a tranny fluid cooler in the radiator. Your engine thermostat is most likely 190*F, so that would be the temp of your tranny fluid. Your truck may also have an additional fin type cooler in front of the radiator to further cool the fluid. If your tranny has a drain plug, it is a good idea to drain the fluid in the pan every year and replace it with fresh fluid.
 
Status
Not open for further replies.
Back
Top