GX460 P2714 P0761 Ultimate Summary and Hope For A Fix Thread

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Has anyone attempted to disassemble the thermostat. It looks like maybe a 28 mm socket may work.

With my thermostat pinned, Hayden installed, I’m still seeing 218-226 on 80 mph interstate runs. Today was a 5 hour drive, most on cruise. Temps rising when TC lockup was lost going up hills. Average was about 222. I believe I could have restricted flow and will attempt to gut the thermostat
 
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gsi18867 said:
Has anyone attempted to disassemble the thermostat. It looks like maybe a 28 mm socket may work.

With my thermostat pinned, Hayden installed, I’m still seeing 218-226 on 80 mph interstate runs. Today was a 5 hour drive, most on cruise. Temps rising when TC lockup was lost going up hills. Average was about 222. I believe I could have restricted flow and will attempt to gut the thermostat
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If those temps are AT temp 1, that’s definitely too high with the hayden. if that’s the TC AT temp 2, that could be possible
 
llm said:
If those temps are AT temp 1, that’s definitely too high with the hayden. if that’s the TC AT temp 2, that could be possible
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Temp 2 always rises when lockup is lost, temp 1 is usually stable but slowly rise through the drive to 222. Engine temp never topped 200. TC temporarily building heat should be expected. Not being able to reduce heat is my concern.
 
gsi18867 said:
Has anyone attempted to disassemble the thermostat. It looks like maybe a 28 mm socket may work.

With my thermostat pinned, Hayden installed, I’m still seeing 218-226 on 80 mph interstate runs. Today was a 5 hour drive, most on cruise. Temps rising when TC lockup was lost going up hills. Average was about 222. I believe I could have restricted flow and will attempt to gut the thermostat
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Local trans temp will always be higher than bulk temp which is why you want lower bulk temps.

I agree with @llm if that's not towing anything it does seem abnormally high for pan temp for driving around. What's your ambeint temp, Stock weight and tire setup? anything mounted to your cooler or blocking it?
 
Going 75-80 with an OEM radiator, Hayden 678, pinned thermostat, and Aisin ATF-0WS in 95-100 degree temps my pan temps run between 170 and 175 degrees.
 
BC11SVT said:
Going 75-80 with an OEM radiator, Hayden 678, pinned thermostat, and Aisin ATF-0WS in 95-100 degree temps my pan temps run between 170 and 175 degrees.
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Yeah, I still have problems I am not sure are solvable with this unit. This was today. 4 hours running around 85 mph from Atlanta to Mobile. Way too hot. Temps back down to 200 after 30 min under 60 mph, including sitting in traffic.

Speed and passing gear usage spike temp, no reverse until sitting in reverse for a few minutes. There’s a fluid flow problem somewhere.

IMG_5257.webp
 
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thescreensavers said:
Nice! I was trying to buy a cheap one to take apart. Thanks for the pics.
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The outer spring is weak, inner is strong, very strong. When it’s closed, the solid plate is pushed up against the body with the ports. When it’s open, it looks like flow is not optimal around the plate. I put it back in with the spring assembly because the mandrel (button?) you push in when you pin it open is only held in place by the o-rings. If it were to somehow get pushed in without the spring assembly, or get pulled in when the transmission cools, you could lose all your trans fluid, IMO. Very little fluid came out when I pulled it. Maybe 3 OZs. I believe it’s a 24 mm fitting. Same as the trans fill plug
 
BC11SVT said:
We need a 160 degree replacement thermostat for these rigs
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Need a replacement spring. The entire assembly is held together with a C clip. It’s by my left thumb in the blurry picture above.

I’m also considering tapping the cap to accept a bolt where the mandrel/button lives so it can be run without the spring assembly
 
gsi18867 said:
Need a replacement spring. The entire assembly is held together with a C clip. It’s by my left thumb in the blurry picture above.

I’m also considering tapping the cap to accept a bolt where the mandrel/button lives so it can be run without the spring assembly
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It might be worthwhile to put it in a pot of boiling water and see how far it actually opens. I've tested engine coolant thermostats that way.
 
Rednexus said:
It might be worthwhile to put it in a pot of boiling water and see how far it actually opens. I've tested engine coolant thermostats that way.
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It would be. It looks like the limit is about a 1/4”.

But I still believe there is a flow restriction around the outside of the plate that sets against the main plug/orifice. I think the diameter of the plate is too wide for optimal fluid flow, especially for a unit without a stock secondary cooler. And at this point the flow path has 2X 90 degree turns very close to one another.

I’m not specifically a fluids engineer, but I’ve run into similar flow path restrictions on oil well production chokes. It can be a problem maximizing flow unless you move to a different set up, a larger choke, or a gutted choke.

IMG_5261.webp


IMG_5262.webp
 
gsi18867 said:
It would be. It looks like the limit is about a 1/4”.

But I still believe there is a flow restriction around the outside of the plate that sets against the main plug/orifice. I think the diameter of the plate is too wide for optimal fluid flow, especially for a unit without a stock secondary cooler. And at this point the flow path has 2X 90 degree turns very close to one another.

I’m not specifically a fluids engineer, but I’ve run into similar flow path restrictions on oil well production chokes. It can be a problem maximizing flow unless you move to a different set up, a larger choke, or a gutted choke.
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I'm not a fluids engineer either, but in my branch of engineering we'd call that a "torturous flow path" :). I'm sure there are some sizeable head losses when viscous trans fluid is pumped through that thermostat, which would then reduce the overall flow rate of cooled fluid coming back into the trans from the radiator.

Perhaps Toyota engineers thought of that and gave the 760F a better pump than the 750F to accommodate the head loss, but I still suspect they hurriedly concocted this system to meet CAFE regs :).
 
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i add no value to this discussion but wanted to say that fluid dynamics was part of my job and this gives me a headache. probably why was and not still am.
 
llm said:
i add no value to this discussion but wanted to say that fluid dynamics was part of my job and this gives me a headache. probably why was and not still am.
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It’s a big part of my job and I love the discussions, specifically around failures in gas/liquid systems. 🤣🤣.

On another note, I finally gave in and put a full bottle of AT205 in. I’m blown away by how fast it has improved function. Less than 15 miles in, I’ve regained full reverse with no hesitation or weakness. Only had 2 drives in that 15 miles. Still had temps rise. Had to clear codes 2X in the 10 mile drive to regain 3-4 shift. Typically had to clear codes or manually shift 10-20 times in that drive.

Improvements came very quickly. Thank you to everyone recommending it. I’m putting another bottle in the garage just in case
 
llm said:
i add no value to this discussion but wanted to say that fluid dynamics was part of my job and this gives me a headache. probably why was and not still am.
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It's quite interesting how often I find myself going back to the introductory engineering classes I took 20+ years ago (physics, statics, dynamics, material mechanics, chemistry, and yes fluid mechanics :)) to support my wrenching hobby/addiction. Understanding those fundamentals really helps when trying to diagnose and/or solve a problem.

Telling my wife "I'm an engineer" when she questions me doesn't help very much, on the other hand ;).
 
gsi18867 said:
It’s a big part of my job and I love the discussions, specifically around failures in gas/liquid systems. 🤣🤣.

On another note, I finally gave in and put a full bottle of AT205 in. I’m blown away by how fast it has improved function. Less than 15 miles in, I’ve regained full reverse with no hesitation or weakness. Only had 2 drives in that 15 miles. Still had temps rise. Had to clear codes 2X in the 10 mile drive to regain 3-4 shift. Typically had to clear codes or manually shift 10-20 times in that drive.

Improvements came very quickly. Thank you to everyone recommending it. I’m putting another bottle in the garage just in case
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It really is remarkable. I'm at 1200 miles now...zero issues. Damn thing shifts like new. Honestly, I'm taken aback by how quickly it seems to have worked...
 
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