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.

 

[Rednexus]

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.

FWIW I now use a Hayden 698 cooler, which has an integrated thermostat that bypasses the external cooler in cold temps. That being said, this setup still over-cools somewhat (not as bad as the thermostat-less Hayden 678 though) when it's bitter cold outside and I still run the rubber block-off.

 

[landtank]

The transmission has a thermostat and appears to cycle the fluid within the transmission until the thermostat begins to open and flow through the radiator.

The reverse should be true.

However there can be a disconnect between the thermostat and that of the temp sensor that can be read.

After seeing the recent rebuild and the amount of heat damage I’m wonder if the transmission thermostat could be faulty.

 

[Rednexus]

The transmission has a thermostat and appears to cycle the fluid within the transmission until the thermostat begins to open and flow through the radiator.

The reverse should be true.

However there can be a disconnect between the thermostat and that of the temp sensor that can be read.

After seeing the recent rebuild and the amount of heat damage I’m wonder if the transmission thermostat could be faulty.

You are missing one component. The thermostat on the side of the GX460 transmission has a warmer that routes engine coolant to the transmission to rapidly increase trans temperatures. As I explained in my other post(s), the A750F/760F generate very little heat when running with the TCC locked. I suspect that if the thermostat was only a thermostat with no warmer and just blocked flow to the radiator that the trans would run <100F during TCC lock conditions in cold temperatures, which is too cold for proper operation and would result in low fuel economy. It is likely that Toyota added the warmer for CAFE/fuel economy reasons as IMO it's a complex and otherwise unnecessary system that the older, less efficient, and more reliable GX470 lacks.

This system certainly keeps the trans running warmer which helps with fuel economy, but the rest of the cooling system (limited to only loops in the radiator and no external cooler) doesn't seem to be able to shed extra heat when the TCC unlocks. I'll repost the photo of my setup I posted a few weeks ago - nearly 90F out and after ~30 miles of highway driving with the TCC almost exclusively locked. Trans temps this low would never be possible in a 460 unless the thermostat/heater is pinned open and disabled, and extra cooling were added to the system.

 

[Acrad]

It seems like every 3UR-FE or 1UR-FE equipped vehicle from 2008+ has this same setup.

 

[landtank]

Back in 2000 people driving 80 series Land Cruisers started having over heating problems. These were typically during summer months when temps got around 100*.
My truck was acutely afflicted by this to a point that towing a small tent trailer through Vermont required many stops to allow it to cool.
This was especially weird as I replaced the fan clutch a few months earlier in preparation for the summer camping.
It didn't take long for the group to realize that the new "Aisin" clutches had a problem.
Comparing the Blue hub Aisin to the previous Black hub clutch it was obvious that the Aisin clutch had far less sheering surface so less cooling ability.
Over the nest month I developed a mod to regain the lost cooling ability and have been selling them since that time back in 2000.

This was the beginning of every clutch delivered to the American market being only marginally acceptable at cooling our trucks.
What you are missing, is that the fan clutch in you truck is only marginally acceptable and you are seeing that on tor screen.

 

[jpeterferrell]

Back in 2000 people driving 80 series Land Cruisers started having over heating problems. These were typically during summer months when temps got around 100*.
My truck was acutely afflicted by this to a point that towing a small tent trailer through Vermont required many stops to allow it to cool.
This was especially weird as I replaced the fan clutch a few months earlier in preparation for the summer camping.
It didn't take long for the group to realize that the new "Aisin" clutches had a problem.
Comparing the Blue hub Aisin to the previous Black hub clutch it was obvious that the Aisin clutch had far less sheering surface so less cooling ability.
Over the nest month I developed a mod to regain the lost cooling ability and have been selling them since that time back in 2000.

This was the beginning of every clutch delivered to the American market being only marginally acceptable at cooling our trucks.
What you are missing, is that the fan clutch in you truck is only marginally acceptable and you are seeing that on tor screen.

I am preemptively changing the fan clutch in my 460 in the next few weeks - I don't get any overheating, but the A/C definitely struggles to get going when the truck is heat soaked during the day, and dramatically improves after driving for 5-10 mins and moving air through the front of the vehicle. I can also...feel that the current fan clutch isn't providing the same noise and resistance I know it should, like on startup, or when I know it's heat-soaked. I think it's the original factory one. I bought the Aisin replacement from RockAuto...hopefully that's sufficient. I'll be doing that when I do the new tensioner/idler/serpentine belt in a week or two.

Update from me, pulled the pan, changed the filter. The pan had definitely never been off before (gasket was rock hard, came off in crumbles), filter had never been changed as far as I could tell. Completely normal light gray paste on all four magnets, no glitter in the fluid. If I didn't know it previously had the codes, it would have looked like a completely normal transmission to me. Filled it back up, set the level, and I've put about 300 miles on it with no codes and perfectly normal shifting, gear engagement, etc!

Next step is adding the Hayden 698 or the straight factory setup. I'll either use the Goliath bracket with the Hayden or just do the factory version with factory parts.

 

[Rednexus]

This was the beginning of every clutch delivered to the American market being only marginally acceptable at cooling our trucks.
What you are missing, is that the fan clutch in you truck is only marginally acceptable and you are seeing that on tor screen.

GX460s and GX470s don't really have engine overheating problems unless there is a burst in the OEM radiator or a coolant leak. I've towed and wheeled extensively with mine (towing up to 5,800# up our steep Ozark hills), including in temperatures up over 100F, it has never had a problem keeping the engine cool. The stock radiator did fine, the CSF aluminum I have now does even better - but I see the biggest different in trans temps, not in the engine. I can't speak for the 80 as I don't own them, but presumably they are a very different vehicle for the 120/150. My buddy has a GX460 and has had the same experience towing a 5,500# boat, although I've been on him to upgrade his trans cooling system and get rid of the Toyota WS.

IMO an upgraded fan clutch certainly won't hurt the situation but won't address the warmer on the GX460 artificially keeping the fluid at 190F at all times, nor the lack of external cooling downstream from the radiator (which really helps with the TCC is unlocked and the trans fluid temp exceeds engine coolant temp). That being said, I will pre-emptively replace my 19-year old fan cutch with 207K on it the next time I change the timing belt.

 

[BC11SVT]

GX460s and GX470s don't really have engine overheating problems unless there is a burst in the OEM radiator or a coolant leak. I've towed and wheeled extensively with mine (towing up to 5,800# up our steep Ozark hills), including in temperatures up over 100F, it has never had a problem keeping the engine cool. The stock radiator did fine, the CSF aluminum I have now does even better - but I see the biggest different in trans temps, not in the engine. I can't speak for the 80 as I don't own them, but presumably they are a very different vehicle for the 120/150. My buddy has a GX460 and has had the same experience towing a 5,500# boat, although I've been on him to upgrade his trans cooling system and get rid of the Toyota WS.

IMO an upgraded fan clutch certainly won't hurt the situation but won't address the warmer on the GX460 artificially keeping the fluid at 190F at all times, nor the lack of external cooling downstream from the radiator (which really helps with the TCC is unlocked and the trans fluid temp exceeds engine coolant temp). That being said, I will pre-emptively replace my 19-year old fan cutch with 207K on it the next time I change the timing belt.

Yeah, not at all. Even in 95+ degree temps my coolant temps run 188-190.
The transmission temp issue in the GX460 has nothing to do with the fan clutch as you stated.

 

[Rednexus]

Yeah, not at all. Even in 95+ degree temps my coolant temps run 188-190.
The transmission temp issue in the GX460 has nothing to do with the fan clutch as you stated.

I was surprised just how big the radiator is when I ripped the front of my rig apart for a bumper install. Don't know why I hadn't noticed this before (considering I've replaced the radiator), but it's about as tall and as wide as Toyota can feasibly stuff in the front of the rig. It must have a ton of cooling capacity - seems that Toyota realized these rigs have a V8, cramped engine bay, weigh 5,000# stock, and usually have dual-zone AC and then added all the radiator they could.

 

[landtank]

A clutch upgrade will positively impact the engine, transmission and AC cooling ability.

And I sell clutches across the spectrum of Toyota trucks and ship around the world. It’s not just an 80 thing.

 

[jpeterferrell]

What do you

A clutch upgrade will positively impact the engine, transmission and AC cooling ability.

And I sell clutches across the spectrum of Toyota trucks and ship around the world. It’s not just an 80 thing.

What do you sell for the GX460?

 

[landtank]

It’s a modified new Aisin clutch same as what is in the trucks now.

 

[Biginboca]

Another update on the AT205. It’s now been almost 4 weeks since I added it. I’ve covered over 1500 miles. Transmission is functioning normally I’ve been driving in D only for well over 1300 miles/3 weeks. I have not had a single hiccup or irregularity in transmission behavior.

Next step will be beginning the cycle of weekly drain and fills of the transmission pan and adding a cooler. Thinking I’ll do weekly drain and fills 3 times before adding the cooler on the 4th and final pan drain and fill. Trying to not introduce too many variables but my original fluid is now approaching 16 years and 160k miles old.

 

[r2m]

I designed my shop to accommodate a lift (footings in the floor, 12' walls with a cathedral ceiling, and it's wired for one) but I can't stomach the $5K+ cost for a non-Chinese knockoff lift right now. I also like the shop being open and not having 2 giant posts in the middle bay, as we also use the shop for many other things (including living it it while waiting for the house to get done!). Maybe in the future, but it would take another project vehicle to justify it.

You guys all make me jealous talking about your 12' ceilings, multi-bay garages, huge home lots etc...
I'm stuck with a one car garage stuffed with surfboards, wetsuits, and beach gear on one wall, the opposite wall is our second fridge, my work bench, tool chest, tools and power tools. I don't even have 220 AC, so I can't even use my welders! Can't even fit a car and when I have to use my table saw, radial arm saw, drill press, etc. I have to move a bunch of stuff outside the garage to get to those tools.
Oh well... What do they say about 'first world problems'? Think I'll just have to walk on down to the beach (100 feet....) and go for a quick swim since the weather is looking like it'll be a sweltering 79°F here today with the water temp hovering 'round 76°F.

 

[Rednexus]

You guys all make me jealous talking about your 12' ceilings, multi-bay garages, huge home lots etc...
I'm stuck with a one car garage stuffed with surfboards, wetsuits, and beach gear on one wall, the opposite wall is our second fridge, my work bench, tool chest, tools and power tools. I don't even have 220 AC, so I can't even use my welders! Can't even fit a car and when I have to use my table saw, radial arm saw, drill press, etc. I have to move a bunch of stuff outside the garage to get to those tools.
Oh well... What do they say about 'first world problems'? Think I'll just have to walk on down to the beach (100 feet....) and go for a quick swim since the weather is looking like it'll be a sweltering 79°F here today with the water temp hovering 'round 76°F.

Yup - we also have the ~2,900 SF nearly-new custom designed and built home next to the shop, both of which are on a multi-acre wooded lot that's both big enough that I can use my tractor on it and far enough outside of town that we can responsibly engage in target practice in the backyard. Oh - no planning/zoning regulations, no HOA, my building permit was only $25, property taxes are maybe $2K a year, and state income/sales taxes are so nominal that I barely notice paying them .

But, every year does involve a pricey vacation or two to the beach, to the mountains, or both .

 

[PinkyPeePaw]

You guys all make me jealous talking about your 12' ceilings, multi-bay garages, huge home lots etc...
I'm stuck with a one car garage stuffed with surfboards, wetsuits, and beach gear on one wall, the opposite wall is our second fridge, my work bench, tool chest, tools and power tools. I don't even have 220 AC, so I can't even use my welders! Can't even fit a car and when I have to use my table saw, radial arm saw, drill press, etc. I have to move a bunch of stuff outside the garage to get to those tools.
Oh well... What do they say about 'first world problems'? Think I'll just have to walk on down to the beach (100 feet....) and go for a quick swim since the weather is looking like it'll be a sweltering 79°F here today with the water temp hovering 'round 76°F.

You in Cali? I’m in San Antonio and my son is stationed in Oceanside. Awesome area but I don’t know how people afford it. I do like So Cal.