At what temp does toyota (WS) AT fluid fail? - Toyota FJ Cruiser Forum
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post #1 of 30 (permalink) Old 11-02-2014, 06:11 AM Thread Starter
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At what temp does toyota (WS) AT fluid fail?

So I have been debating whether to get an AT cooler or not. I have read a lot on here about this. What I have read here is that if you tow, which I do not, or if you go off road (which I do alot) you should use a supplemental cooler

When I bought my 08 earlier this year with 60K, it has the dreaded "shudder" which I discovered before I modded it thankfully, it was bone stock CPO when I bought it

This tells me:
- the service interval for WS if less than 60K since changing the fluid resolved the issue (for now)
- a bone stock FJ that does not tow can still fry its tranny fluid pretty fast
- ...or... perhaps the prior owner abused it although that does not seem consistent with an FJ that was dealer serviced like clockwork as per the carfax

Anyhoo...

I bought a scanguage 2 and set it up just in time for a off road run yesterday. It can read tranny fluid temp on FJ's with an entered extra code

Here is what I saw:
- tranny fluid temp of around 150-180 with light secondary hwy driving
- nothing more than 180 off road (in 4 low at all timess off road), even longish steep rocky climbs, it would maybe go up 5 degrees under loads off road vs flat dirt trail. Even towing a Jeep out of muddy ruts for 100 yds had no impact
- The temp rise very fast going up hills on pavement in 2wd, I would get peak temps of 200-210 without being aggressive at all or heavy on the gas, despite outdoor temps of 35-40 F

These trannies run hot it seems (c/w what I have read here before), without much provocation, so:
-either they should all get a cooler?
- or toyota WS is fine with regukar temp spikes of 220-230 (where I am guessing it would get in warmer weather)

Thoughts? Does anyone know the temnp at which this fluid starts to fail??

--2008 FJ Cruiser, 3" Toytec/Bilstein lift, 32" Cooper S/T Maxx, All pro sliders, Ricochet skids, LR UCA's
--2014 WK2, ORA II, Cooper 32", Quadralift, MOPAR rock rails (daily driver)
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post #2 of 30 (permalink) Old 11-02-2014, 10:41 AM
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Re: At what temp does toyota (WS) AT fluid fail?

I think the larger concern is deterioration of elastomeric seals in the transmission (static O-rings, sliding piston seals, etc.) rather than "breakdown" of the WS fluid itself. There is no question that internal transmission components (seals, clutches, solenoids, sensors, and the fluid) will have longer service life and reduced probability of failure if the peak transmission temperature is reduced. Even if you don't tow, a properly-installed transmission cooler (and regular fluid changes to remove clutch wear debris) should extended transmission life.

I recently took a little drive in the local S. Cal mountains (Mt Baldy>Glendale Ridge Road>San Gabriel Canyon) and was shocked to see hot the transmission got even under very mild load conditions.

I'm using a Bluetooth OBD-II dongle and Torque Pro to monitor and record a whole list of vehicle parameters on my '14 FJ. I'm still breaking in the driveline at about 2K miles, so while climbing the mild grades engine RPM did not exceed ~2500 RPM, and max throttle opening wasn't over 30 - 50%. Vehicle is dead stock, and was completely empty except for driver and a full tank of gas.

The A750F transmission actually has two fluid temperature sensors, one in the pan and the other at the outlet of the torque converter. On this 80F day, both sensors were reporting fluid temperatures of around 160-165F at 65-70 MPH on the freeway. The lockup clutch is locked at these speeds, so there's no heat being generated in the torque converter.

As soon as I started climbing even a mild grade, transmission fluid temperatures increased dramatically. Pan temp reached 209F, and TC outlet temp immediately spiked to just under 230F. I'm sure that if the vehicle had been fully loaded, or was being driven a little less conservatively, temps would have been substantially higher. I can't imagine what fluid temps would have looked like with a fully-loaded vehicle, towing a medium-weight trailer, climbing long, steep grades in the summer.

I've now got a Hayden 679 transmission cooler sitting on my workbench, waiting for installation...
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post #3 of 30 (permalink) Old 11-02-2014, 01:28 PM
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Re: At what temp does toyota (WS) AT fluid fail?

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FJtest previously said: View Post
As soon as I started climbing even a mild grade, transmission fluid temperatures increased dramatically. Pan temp reached 209F, and TC outlet temp immediately spiked to just under 230F. I'm sure that if the vehicle had been fully loaded, or was being driven a little less conservatively, temps would have been substantially higher. I can't imagine what fluid temps would have looked like with a fully-loaded vehicle, towing a medium-weight trailer, climbing long, steep grades in the summer.

I've now got a Hayden 679 transmission cooler sitting on my workbench, waiting for installation...
Me thinks this is beacause Toyota programmed the tranny to take an act of God before kicking down a gear. For whatever reason this tranny LOVES to unlock the converter and run like that forever before kicking down a full gear.

It's like they chose MPG over tranny life. It absolutely bugs the crap out of me and I'm constantly having to choose 4th myself going up long grades long before the tranny should be choosing to do it on it's own.

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post #4 of 30 (permalink) Old 11-02-2014, 01:57 PM
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Re: At what temp does toyota (WS) AT fluid fail?

If you consider an average outdoor temp of 80-F then:
2. Your normal high temp of 180 + 35 = 215 is typical.
3. Your peak temp of 230 + 35 265 is typical.
4. the rubber seals are Either FKM-Viton or Fluoro-Silicone and can handle constant running temperatures of 300+ for thousands of hours.
5. The plastic seals and rings are made from PPS or Teflon or Torlon and can easily operate at 300+ for thousands of hours
6. Lowering your temps by 20F will increase your seal rubber life by 50% by decreasing the thermal expansion and resultant friction as well as fluid degradation (shear) and loss of lubricity.
4. I have an in-line with an electric fan which by-passes the radiator. It is thermostatically controlled (adjustable) so it only runs when the fluid reaches 190-F. This is great for summer, but in winter you want fast warm-ups and not running too cold, so I shield the cooler a bit. I am considering a spin-on filter as well to help remove particulates in the main flow stream?

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post #5 of 30 (permalink) Old 11-02-2014, 02:21 PM
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Re: At what temp does toyota (WS) AT fluid fail?

Quote:
lqdchkn previously said: View Post
Me thinks this is beacause Toyota programmed the tranny to take an act of God before kicking down a gear. For whatever reason this tranny LOVES to unlock the converter and run like that forever before kicking down a full gear.

It's like they chose MPG over tranny life. It absolutely bugs the crap out of me and I'm constantly having to choose 4th myself going up long grades long before the tranny should be choosing to do it on it's own.
In the situation I described, I don't think my speed ever got high enough to fall within the range of lockup clutch operation (>36 MPH), so the difference between pan and TC outlet temperatures was probably just the result of fluid shearing in the TC. (It may also have been influenced by slippage of the TC lockup clutch.)

The main concern I have about the A750F is the tri-mode lockup clutch. Toyota's description implies three modes of operation: locked, unlocked, and "intentionally slipping". Given the high incidence of lockup clutch "shudder" problems reported with high-mileage A750F transmissions, wearout of the lockup clutch caused by the "slip-mode" may be the single most common failure with this transmission.

And, I'm not sure there is anything the driver can do to minimize the amount of time the lockup clutch operates in slip-mode.
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post #6 of 30 (permalink) Old 11-02-2014, 04:56 PM
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Re: At what temp does toyota (WS) AT fluid fail?

Quote:
CurbCrawler previously said: View Post
If you consider an average outdoor temp of 80-F then:
2. Your normal high temp of 180 + 35 = 215 is typical.
3. Your peak temp of 230 + 35 265 is typical.
4. the rubber seals are Either FKM-Viton or Fluoro-Silicone and can handle constant running temperatures of 300+ for thousands of hours.
5. The plastic seals and rings are made from PPS or Teflon or Torlon and can easily operate at 300+ for thousands of hours
6. Lowering your temps by 20F will increase your seal rubber life by 50% by decreasing the thermal expansion and resultant friction as well as fluid degradation (shear) and loss of lubricity.
4. I have an in-line with an electric fan which by-passes the radiator. It is thermostatically controlled (adjustable) so it only runs when the fluid reaches 190-F. This is great for summer, but in winter you want fast warm-ups and not running too cold, so I shield the cooler a bit. I am considering a spin-on filter as well to help remove particulates in the main flow stream?
CurbCrawler -

Great post! The point that I was trying to make is that even though my transmission temps were "normal", I was just puttering along on a deserted mountain road with minimal throttle and an empty vehicle. Maybe its just hyper-conservatism, but I'd strongly prefer to never see a trans temperature anywhere near 300F. I do plan to tow, and most of my off-road driving is in desert areas, so if an auxiliary cooler will help keep peak transmission temperatures below 275F, then that's OK with me.

I tend to keep my vehicles for 200K miles or more, and I'd prefer NOT to have to replace the transmission during that period.
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Last edited by FJtest; 11-02-2014 at 06:18 PM.
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post #7 of 30 (permalink) Old 11-02-2014, 04:59 PM Thread Starter
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Re: At what temp does toyota (WS) AT fluid fail?

Thank you for the above comments and info

does anyone know the temp at which the fluid gets compromised?

--2008 FJ Cruiser, 3" Toytec/Bilstein lift, 32" Cooper S/T Maxx, All pro sliders, Ricochet skids, LR UCA's
--2014 WK2, ORA II, Cooper 32", Quadralift, MOPAR rock rails (daily driver)
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post #8 of 30 (permalink) Old 11-02-2014, 06:12 PM
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Re: At what temp does toyota (WS) AT fluid fail?

Quote:
gabbagabba previously said: View Post
Thank you for the above comments and info

does anyone know the temp at which the fluid gets compromised?
I don't think you can assign some specific temperature where the fluid suddenly "gets compromised". Like most lubricants, as temperature increases, viscosity and film strength decrease, the rate of oxidation increases, the lighter fractions vaporize, acidity increases, etc.

One reference states that the rate of oxidation doubles for every 18F increase in oil temperature beyond 165F.
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post #9 of 30 (permalink) Old 11-02-2014, 06:58 PM
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Re: At what temp does toyota (WS) AT fluid fail?

Good post-you provide valuable trans temp data for no aux cooler.
I worked in the automotive aftermarket for nearly 30 years and never saw a definitive statement to answer your question. Data sheets exist for oils and fluids (some are well guarded as the manufacturers of those fluids and the equipment they are used in often wish to advertise the capabilities as they see fit). Back when fluids and labor costs were cheap the auto companies recommended frequent changes (preferably at the dealership). This boosted profits. Later, when maintanence costs soared (and before synthetics really made some of today's change intervals realistic) they changed their tune and doubled the intervals just so they could advertise a vehicle's "low maintanence costs." Who cares if it prematurely fails-that boosts profits as well. Anyway, the data sheets will give specific numbers for the characteristics FJTest highlighted. But as also stated, these processes are gradual. Also, temps, pressures, shear loads are constantly changing in the mechanisms these fluids are used in.
If I may offer an example to help, here is what I have found so far with my FJ:
https://www.fjcruiserforums.com/forum...ns-towing.html
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post #10 of 30 (permalink) Old 11-03-2014, 08:26 PM
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Re: At what temp does toyota (WS) AT fluid fail?

Keep in mind one thing about transmission fluid temps... What ever engine temperatures are, this will be the lowest the transmission fluid temp will ever be without the use of an aux cooler. Fluids do break down at higher temps; however, synthetic fluids have raised this boiling point pretty high. 90% of the heat generated in a transmission is caused by the Torque Converter and the lock-up clutch at full lock also reduces the temperature; however, lockup will not occur in 2nd gear.

The internal thrust washers and bushing usually are damaged long before the new fluids break down due to boiling. Keeping the fluid clean and maintained is the greatest benefit one can do for the transmission. I used to put temperature strips on the pan so I could see what max temp the fluid reached, then I would decide from there if a cooler was indeed needed.

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