GX460 P2714 P0761 Ultimate Summary and Hope For A Fix Thread

[Rednexus]

I don’t think this is the case. With older systems yes but in case the transmission has a thermostat in the circuit. It won’t circulate fluid until the thermostat opens.

This is one of the reasons I’m tuning the fan clutch. You can’t overcool the transmission but sure as hell can over heat it.

You definitely can over-cool these transmissions. The A750F/760F generate very little heat when running with the TCC locked as there is no slippage occurring and the only heat is from the fluid getting pumped around. My A750F with a Hayden 678 would run as cool as 120F after 30-40 minutes of cruising during below freezing temps outside. Since heat flows from warmer to colder, this means the radiator was actually already warming up the trans fluid - and the Hayden 678 (downstream of the radiator) was then shedding the heat back to the cold air. Had I been running a standalone system as proposed, it would have been running even cooler as there would be less heat going into the external cooler to start with.

Shifting was harsh with this setup, so I made a rubber cover that blocked up about 2/3 of the Hayden 678 for winter use. I am not sure what other problems can be caused by an over-cooled transmission, but it would be running well outside of Toyota's design parameters. IMO they run fine in the 150-190F range, but not any colder. Mine's never gotten much above 200F with a CSF radiator and a Hayden, and that includes lots of towing in 100F+ temps.

 

[landtank]

You definitely can over-cool these transmissions. The A750F/760F generate very little heat when running with the TCC locked as there is no slippage occurring and the only heat is from the fluid getting pumped around. My A750F with a Hayden 678 would run as cool as 120F after 30-40 minutes of cruising during below freezing temps outside. Since heat flows from warmer to colder, this means the radiator was actually already warming up the trans fluid - and the Hayden 678 (downstream of the radiator) was then shedding the heat back to the cold air. Had I been running a standalone system as proposed, it would have been running even cooler as there would be less heat going into the external cooler to start with.

Shifting was harsh with this setup, so I made a rubber cover that blocked up about 2/3 of the Hayden 678 for winter use. I am not sure what other problems can be caused by an over-cooled transmission, but it would be running well outside of Toyota's design parameters. IMO they run fine in the 150-190F range, but not any colder. Mine's never gotten much above 200F with a CSF radiator and a Hayden, and that includes lots of towing in 100F+ temps.

The A750F doesn’t have a thermostat controlling the fluid flow so yes you can overcool it as I said older systems worked that way. That does not apply to the GX460 as it has a thermostat to control flow. And you were talking about the GX460 at that moment.

 

[Rednexus]

The A750F doesn’t have a thermostat controlling the fluid flow so yes you can overcool it as I said older systems worked that way. That does not apply to the GX460 as it has a thermostat to control flow. And you were talking about the GX460 at that moment.

The laws of thermodynamics apply go a GX460 just as well as they do to a GX470 . Heat flows from warmer to colder - that's all you need to know to understand how the system will operate based on TCC lock/unlock status, engine coolant temperature, exterior air temperature, and the presence (or lack thereof) of external coolers.

Edit: I do see that the 460 cooler seems to route engine coolant to the transmission - perhaps that is the difference between the two systems, and would result in the trans fluid getting warmed up in cold weather which the 470 is unable to do. With that system your trans will always be operating at around 190F as a "starting point". I usually run ambient plus ~80 degrees out but never over 170F cruising with the TCC locked. You could bypass the OEM radiator cooler into an external trans cooler and not pin the thermostat open, thereby avoiding overcooling in the winter, but unless the thermostat is pinned open you'd still be running 190F as your starting point (and therefore hotter than my system). If I had a GX460 I'd personally figure out a delete for the whole warmer/thermostat system and replicate the GX470-style system I have which has less failure points all the way around, and provides improved engine cooling while deleting the burst-prone Toyota plastic radiator.

 

[BC11SVT]

I don’t think this is the case. With older systems yes but in case the transmission has a thermostat in the circuit. It won’t circulate fluid until the thermostat opens.

This is one of the reasons I’m tuning the fan clutch. You can’t overcool the transmission but sure as hell can over heat it.

Maintaining the thermostat forces the transmission to run 190+ regardless of cooling mods.
IMO, it's best add an auxiliary cooler, keep the radiator in the loop, and pin the thermostat open if your goal is to maximize transmission longevity.

You can always unpin the thermostat it if the temps drop below zero.

I really wish it was possible to modify the thermostat to open @ 160, that would be ideal.