Just take you time doing it and you should be fine.
I'm surprised the temp still climbed with the thermostat out. I would assume once it crossed halfway on the gauge that you heard the fan kick on.
When you turn the AC on the fans should have automatically kicked in.

I know this may seem obvious, but did you check that there is nothing stuck in front the AC condenser that may be restricting air flow to the rad?

Throwing out my prediction now...you will install the Aisin thermostat and replace the waterpump, and the issue will still be there.
Then you'll change the rad and it will be fixed.
I know you said that you flushed water through the rad and it came out as fast as it was going in...but the symptoms that you are having are most commonly caused by a plugged/semi-plugged rad...now that you eliminated the original thermostat.
Keep in mind that even with the bad thermostat the issue hasn't changed...with no thermostat the issue didn't change.

 

Damn, is there anything I can flush the radiator with instead of replacing it?

 

I'm not sure if there are any chemical flushes, but perhaps a local rad shop can do it. Those kinds of shops are a dying breed where I am.

Prior to this all starting when was the coolant replaced last?

 

I'm going to drain the rad, pull the lower hose and just flush the radiator by itself with prestone radiator flush + cleaner. My idea is to just pour it through the top and collect it at the bottom a few times then plug the bottom and fill it up and let it soak a while and flush it out with distilled water and see if anything comes out. I'd really prefer not to cycle that stuff through the whole system if I can avoid it and I'm hoping I don't have to pull the radiator, looks like you need to remove the font bumper to do it.

I drained the rad and refilled with the zerex Asian vehicle red coolant every 50k, I've never drained and flushed the whole system, I figured if I just did a drain and fill every 50k I really wouldn't need to.

 

the inside of an original water pump with 192k



looks pretty damn clean, impeller seems fine.... i did see what COULD be some leaking, but it could have been from coolant that leaked down pulling the thermostat twice? I never saw any coolant on the ground under the car and the inside of the pulley just had dirt, no dried coolant so idk..




printed a picture of the water pump, taped it to cardboard and punched the bolts through as i took them off to keep track...thought it was a good idea




waiting on amazon to deliver the new one today, going to prestone and citrus flush (mercedes method) the radiator by itself...i was going to take it out but there's just too much to pull off to get it out

I'll update if the new aisin pump, aisin thermostat, radiator flush fixes it. God help me if it doesn't.

 

Im a retired mold maker and I built the tooling for this water pump (if it’s an Aisin). Brings back memories

 

The inside of the waterpump is so clean you could eat off of it...I wouldn't recommend it though lol!

That's actually a legit good idea to print out the pic of the waterpump for bolt hole reference.
From the pic of the breather hole I would say the waterpump was weeping coolant slightly...which Toyota will say is normal to an extent.
Certainly the waterpump was on the road to needing replacement, but it would have held out a little longer...I would say no regrets replacing it now.
That amount of weepage wouldn't have caused an overheating issue though.

Any chance you can access the block drains for the coolant? Now that you have the waterpump and thermostat out, you could flush the engine side of the coolant system with a garden hose...but you'll want to drain out as much of the water when you're done...via the block drains.
In case you're thinking "where are the block drains?"...

There one on each side of the engine...it's like a spigot...loosen the bolt a couple turns and the coolant comes out the spout...when it's empty just tighten the bolt back up. I think the bolt is a 10mm.

 

got the new water pump on, while the radiator was disconnected I filled it up with prestone radiator flush and let it soak for 30 minutes...no sediment came out, same with the citric acid flush, flow is fine water comes out like a fire hose at the bottom.

same damn issue!!!!!!! could it be the coolant temp sensor? I mean do those even go bad wtf? really feel like just driving it until it blows up then buying the IS500. There's no leaks from new pump, this sucks.

edit: I used a spill proof funnel and ran it for 30 minutes hot and waited until all bubbles came out, turned car off, turned it on again 5 times and more bubbles came out, did it another 5 times until no bubbles at all...

 

To recap you have an OEM thermostat and waterpump, flushed the rad, and filled with new coolant...and it still overheats when you get on it?

If the temp sensor was bad, then that means it failing only under a very specific condition...which wouldn't make much sense. If you're wondering where the sensor is, it's on the back of the engine above the very top middle of the transmission.
To get to the sensor i think the Intake Manifold would have to come off at least.
The only other thing I can think of is a head gasket...but that is so uncommon for these engines it's not even funny...to the point it's never been heard off. It's not like an '86-92 Supra that eats head gaskets for breakfast.

This one is a head scratcher.

 

I'm lost seriously. I forgot I had an old OBD-II bluetooth scanner in, I downloaded the app and drove...if I get on it, temp got up to 237F... turn heater on full, dips back to a hair below half on gauge and says around 212F...I'm out of ideas. This means the temp sensor is working right?

If it was a head gasket I would be losing coolant, or getting chocolate milk in oil or coolant right? I have neither

 

For the 350 normal coolant temp reading is between 167-212F...factors affect this like altitude, ambient temp., blah blah blah.
From your own account with the scan tool the sensor seems to be working.

I'm really hard pressed to think this is a head gasket issue.

If you didn't turn the heater on would it eventually come down on it's own? Or just keep climbing?

 

just stay hot, once i turn the heat on blast it drops to normal within a minute, maybe a minute and a half...rad fans come on, I'm so lost here, I'm ready to call lexus and take it in for a diagnostic who the hell knows how much that will cost...FML!

 

I'm running out of reasonable or rational suggestions.

I'm assuming you've had the car several years and this is the first time it's had this issue?

If you had access to a coolant system pressure tester, you could pressurize the cooling system to 17 PSI and watch the gauge to see if it drops.
If it drops and you can't see a leak around the engine or inside the car, then the issue is internal to the engine...which brings us back to head gasket.

The coolant pressure tester is basically a short thick bicycle tire pump looking tool with a gauge and a short hose w/ an adapter that looks like a rad cap.
You remove the vehicles rad cap, install the tool, and pump to 17 psi by hand...then watch the gauge for the next 5-10 minutes to see if it moves or not.
Because the cooling system is sealed, the pressure should not drop at all.

 

just ordered one, will get in a few days...I'll update them. Might just order a temp sensor anyways, really don't want to pull all that stuff off to change it but eh

looks like the way to do the coolant temp sensor...battery, intake, looks like MORE coolant fun with the heater core hoses? I can't wait.

 

The ECU has 3 codes for the temp sensor...You'd figure if something was up with the sensor it would have tripped one of the codes.
I don't think you need to move the heater hoses, but there may be a fuel line in the way.
Honestly though I don't think the sensor is faulty at all...if anything it's working perfectly fine.
At least do the pressure test first before anything else.