Ha ha nooooooooooo your making it hard for me HK1837 I did all that research over a Tranny Cooler years ago and made my mind up then
I had an 1,800 Kg Flightcraft ski boat with a nice little LT1 Chev that I towed.
Rodney from what I understand is respected in the industry I trust people with experience in a field and it makes it very difficult to say ----- but I'm going to have to trust the Toyota Engineers on this one so maybe he will see my money anyway in a rebuild - I hope not as fair is fair I will owe you beer for me getting it worng
In addition to the reasons above why I'm not going to stray too far away from what Toyota Engineered.
Yes they do get it wrong sometimes!The fliud check level procedure requires the A750 to be at 46 to 56 degrees c in the sump via a scan gauge (directly to the sump sensor not at the Converter) or the Toyota check light procedure and that's just at idle. But you start this procedure at less than 30c topping up the sump. Once you have topped it up you heat it up to 46 to 56c and let excess oil drain out of the sump. This alone as an engineer myself points to the fact that 60c is what Toyota Engineers intended the Transmission temp to be in service.
40 to 60 degrees seems to be what people in the USA are getting in normal driving and 80c working the torque convertor hard and it's what I have got here. Please note this is at the sump again.
Even the A750's in the Candain sold Tacomas (which are equiped with a transmission heater via engine heat not torque convertor) return similar temps - modern convertors simply do not generate enough heat anymore like old TroubleMatics or Turbo 400's as they are programmed to lock up ASAP all the time; unlike a Turbo 400 which does not have a lock up convetor and is one of the reasons it generates so much heat plus compared to modern autos it wasted a lot of energy just to run it.
The hottest my A750 has gotten is almost 90 degrees - and that was not towing it was around town when the torque converter was actually working most and it was one of Sydney's hottest days with my cranky wife yelling at me because we were late ------ we were late because I was playing with a mates Scan Gauge I borrowed
80 Degrees Centigrade is normal for an engine and engine seals. The 1GR-FE V6 Thermostat is not fully open until I think 84 Degrees so it's not like the Seal Tech or Oil Tech is not available for the Transmissions.
So given the above that internal sump temperatures unloaded and loaded are the similar I would have to conclude the temp range above is what the Toyota Engineers intended and as I cannot disprove it Like Dyno testing a standard Toyota Air Box V's a TRD CAI I'm going to have to trust the Toyota Engineers on this.
I would though however respectfully disagree and I absolutely mean no offence about your experience with older transmissions, don't worry I have had my problems with them too - Modern Transmissions are light years ahead of the Turbo 400 which was first sold in the 1960's, both in terms of seals and how they operate.
The Turbo 400 had no lock up convertor and was put into vehicles by companies that did the least they had to do to sell vehicles and the coolers were never big enough. With no lock up convertor (and in my case) towing a boat it would get stinking hot because as you know the convertor would be slipping - no lock up. Couple this together with 1960's seal technology ----- remember Chev and Holden were still using rope seals YES rope seals around the crank and sump in the 1970,s ------ and low temp ATF (Auto Trans Fluid) plus old technology clutch material also would fall to bits with any high temps and there would be problem after problem if not kept cool.
Towing with an A750 - and possibly most modern Transmissions I remember a member on here Hilux Maxx posting up a warning about towing with these years ago and he was 100% right. He basically said people when towing with one of these or any Auto forget the basic principles of towing. If you were in a 5 speed manual you would never labour the engine in 5th or the overdrive up a steep hill as it can damage the gear box and possibly the engine. He suggested pulling it down to 4th for steep hills because the Toyota ECU has its own mind made up and will always push to 5th for economy.
When I looked into this I found out other things - the A750 could be excused as a 6 Speed Auto. You may have noticed that it will uncouple its lock up convertor on the Hi-way in 5th to give you an artificial extra gear rather then changing down a gear. Now this is great and all but when your towing if the A750 stays in this unlocked mode that's when I see high towing temps.
So I can highly recommend Hiluxmaxx advice when towing heavy with the A750 chose wisely that 5th gear. That's what I have always done and never had a high temp in the Auto.
The last thing that may interest you as I know you have the 1GR-FE is that the TRD CAI that I installed that reduces the load that the ECU sees has also helped with Auto Temps as the Auto does not unlock as frequently or hunt gears (not that it was that bad anyway).
Anyway like I said I will have to trust the Toyota Engineers on this as I believe installing a cooler without a Thermostat to control temperature is not how it was designed by people much smarter than me. So lets agree to disagree.
Cheers