Should I change the ATF after reaching 266ºF

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Hello. Last time I went to replace the ATF of my Toyota Land Cruiser automatic transmission, the mechanic replaced the stock radiator with an aftermarket one that was supossed to be better. The results were terrible, it was ok in overdrive (it has 3 speeds plus overdrive) as the torque convertor was locked, but, as I had to slow down and running up a mountain pass, the temperature started to raise easyly over 212ºF and I reached peaks of 266ºF. As I was very busy at the time and the automatic transmission specialist was far from me, I had to drive the car for a month and completed 2000 miles. Hopefully, most of them were on the highway where the temperature remained under 190ºF, but I reached the 266ºF at least 3 times. and temperatures like 240ºF quite often. Just peaks as I stopped as soon as I realized but there they were. Now I have fixed the cooling system and I stay under 175ºF most of the time with maximums of 210ºF, but I've been told that the oil can be damaged after having reached those temperatures. It's a fully synthetic Dexron III, that should be able to stand higher abuse, but I don't know to what point. It looks and smells like new, so I guess it's not burned, but maybe it has formed varnishes what is hard to tell as I haven't got any place to analise atf here. The oil is only 4000 miles old now. Do you think I should change it before it damages my transmission, or should I wait till the next oil and filter change (I do it every 15000 miles). Thanks in advance.
 
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It should be fine if the ATF is synthetic, so it should be fine. You just gave it a good workout. If you're still worried, you could always change it a few thousand miles early....
 

ecco123

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Thank you guys. I think I'll wait till making 10000 miles and then change it to Castrol Transmax Z, on what I've read great reports.
 
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When you do change it out, maybe take a uoa to see if you caused any damage...that way you'll know if you ever routinely hit those temps again.
 
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 Originally Posted By: ecco123
Last time I went to replace the ATF of my Toyota Land Cruiser automatic transmission, the mechanic replaced the stock radiator with an aftermarket one that was supossed to be better.
Hmm, maybe the mechanic just wanted your good Toyota radiator? I read somewhere (maybe the Popular Mechanics book) that OEM radiators are often very good, and after-market ones can be [censored], so you should hold onto your car's original radiator as long as possible. The same applies to bumper covers. Since you reached those very high temperatures with the aftermarket radiator, I'd ask the helpful mechanic a few questions: like where is my Toyota radiator :-) You next wrote:
 Originally Posted By: Ecco123
Now I have fixed the cooling system and I stay under 175ºF most of the time with maximums of 210ºF...
What did you have to do to fix the cooling system?
 
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What generates the heat in an auto transmission is the torque converter ,that is where the oil comes from when it is routed through the cooler before being returned to the pan.
 
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When the torque converter is locked up, an auto tranny still churns oil to make heat, and most importantly, the oil pump will be the root of much heat. Also, a bad radiator will heat up the trans oil much hotter than it would otherwise be. Even locked up, an auto tranny car sucks more power than the same car with a manual trans. 5 -20 HP or so. This translates into heat.
 

ecco123

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 Originally Posted By: Built_Well
 Originally Posted By: ecco123
Last time I went to replace the ATF of my Toyota Land Cruiser automatic transmission, the mechanic replaced the stock radiator with an aftermarket one that was supossed to be better.
Hmm, maybe the mechanic just wanted your good Toyota radiator? I read somewhere (maybe the Popular Mechanics book) that OEM radiators are often very good, and after-market ones can be [censored], so you should hold onto your car's original radiator as long as possible. The same applies to bumper covers. Since you reached those very high temperatures with the aftermarket radiator, I'd ask the helpful mechanic a few questions: like where is my Toyota radiator :-) You next wrote:
 Originally Posted By: Ecco123
Now I have fixed the cooling system and I stay under 175ºF most of the time with maximums of 210ºF...
What did you have to do to fix the cooling system?
Very probably that he got my stock radiator. I don't trust that mechanic anymore. When I asked him about the old radiator he said "I put it in the bin, it was rusty and useless". He and his radiator are what are useless!! Anyway, I don't gain anything by getting angry now. I solved the problem installing this radiator: http://www.bulkpart.com/Merchant2/mercha...Product_Count=5 It came with a cold weather bypass, but I had to remove it cause it was opening way too late, when the temperature were over 220ºF. I don't know if it's damaged or bad calibrated. This is it: http://www.bulkpart.com/Merchant2/mercha...Product_Count=7 By the way, now that we talk about this, I'm afraid in the winter I could have problems by having too cold ATF. Now if I cruise on the highway at moderate speed the temperature drops to 160ºF, so it will be even cooler on the winter. I've been told that too cold ATF is almost as bad as too hot. Some other people don't think so at all and say hot ATF is the only problem. What do you think?
 
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ecco123

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 Originally Posted By: unDummy
266 average temp makes you wonder what the 'hot' spots were???? Flush it out.
Well, in fact, my Transmission Temperature Gauge sender is located at the hottest point according with the manual (is an specific gauge for this vehicle) just after the oil leaves the tc. I will flush in a few miles anyway for peace of mind. Will it be enough to flush it myself just the oil in the pan (5 liters out ot 9) or should I take it to a place with flushing machines to completely remove all the oil?
 
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Where you are measuring the trans temp? If at the cooler "out" line, I wouldn't be worried. Those temps sound pretty normal because the cooler out is direct from the hottest part of the AT, the torque converter. If the numbers you stated were from the pan area, then the cooler out temps would have been well over 300 degrees and I'd be a bit more worried. It's time at temp that kills ATF. If it's a good oil, a few temp spikes wouldn't hurt all that much but 2000 miles at those temps could be problematic. I believe you could tell a lot by looking at the fluid and smelling it. If its gone dark and has a burnt odor, I'd change it ASAP. If not, run it the remaining 11K on the OCI... but not a mile over!
 
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Perform a cooler line flush yourself. It will accomplish the same thing as something like a T-tech but its free. As far as the fluid being too cold, Its more of an issue with the torque converter not going into lock-up that you are worried about. Some cars are sensative to this after coolers are installed. As long as you have a thermostat you will have no issues.
 

ecco123

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 Originally Posted By: Jim Allen
Where you are measuring the trans temp? If at the cooler "out" line, I wouldn't be worried. Those temps sound pretty normal because the cooler out is direct from the hottest part of the AT, the torque converter. If the numbers you stated were from the pan area, then the cooler out temps would have been well over 300 degrees and I'd be a bit more worried. It's time at temp that kills ATF. If it's a good oil, a few temp spikes wouldn't hurt all that much but 2000 miles at those temps could be problematic. I believe you could tell a lot by looking at the fluid and smelling it. If its gone dark and has a burnt odor, I'd change it ASAP. If not, run it the remaining 11K on the OCI... but not a mile over!
Yes, as I posted before, the temperature is measured as it leaves the tc, at it hottest point. I've reached 266ºF peaks about three times for a maximum of 5 minutes each time I believe. The fluid is fully syntetic and it looks and smells as new. I know it's not burned, just the varnishes that may have been formed worry me a little.
 

ecco123

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 Originally Posted By: AzFireGuy79
Perform a cooler line flush yourself. It will accomplish the same thing as something like a T-tech but its free. As far as the fluid being too cold, Its more of an issue with the torque converter not going into lock-up that you are worried about. Some cars are sensative to this after coolers are installed. As long as you have a thermostat you will have no issues.
When you say thermostat you mean the cold weather bypass?. I had it but I had to remove it as it was opening too late and the transmission was running hot again (not as hot as before, but hot anyway). What's the minimum operating temperature I should keep the transmission at?. I could cover the new radiator in winter, or cover it parcially if I saw the transmission struggling to reach an acceptable temperature.
 

ecco123

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Well, it'd be cheap in the US, but here is not so cheap. It would if I were using any Dexron III fluid, but the guy that sold me the Transmission Temperature Gauge told me to use only fully synthetic Dexron III (or higher) transmission oil. I took his advice and used so in the last oil change. The could only find fully syntetic Dexron III fluids from Amsoil, Castrol and Alison. Amsoil and Alison aren't available in Spain so I have to import them. Castrol is, but, very funny, the spanish Transmax Z (the one I've been recommended to use) is totally diferent than the australian Transmax Z, different viscosities, doesn't meet the Dexron III approval..... So I had to import the oil, and I ended up paying 160€ (about 220 us dollars). I have only used that oil for 4000 miles, so you understand that I don't feel like paying another 160€ unless it's really necessary.
 
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As I said, ecco123, 266F is not a killer temp from the converter. 200F in the converter is routine but when the lockup is disengaged, the converter slips more and temps go up. Automatics with lockup converters usually have very "loose" converters that make more heat when not locked. I had a vehicle in which sensors were fitted to the pan, the out line and the return line. On that trans, over 200F was fairly routine. A good fluid can handle 250+ very well in short spurts. As I said, it's time at temp that counts more than the actual temperature reached. Your saving grace is that you only run 15K intervals. I doubt any varnish has formed but if it has, when you change (I believe you said you were 4K into a 15K OCI) the new oil will start to break it down. Unless you used some kind of a cleaner, what would be the difference in changing it today? If the fluid still has a nice color and smells normal, it's fine.
 
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Fluid decays on a TWA basis (time weighted average). The more you're at high temps ..the shorter its life. This is a separate issue of the trans internals. Shorten your interval due to these events.
 
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