In today’s 11AM, I noticed my coolant reservoir almost bottom, I add some coolant in there and drive about 20 miles, and I checked the vehicle at 6PM, vehicle still little bit hot, the level is lower than before, and 10PM, I checked again, the level is almost bottom again, nothing on the ground and radiator, and don’t have any symptoms of valley plate leaking. Still confused

 

It's harder to diagnose a valley plate leak, need a boroscope to confirm if you don't see any residue rear of engine or on the ground.

 

same thing happened to my 2014 GX460 couple months at 95k miles.
it was the radiator or radiator cap (pink residual on driver-side of radiator). I replaced the radiator and then problem solved (so far)

 

Interesting observation as I have a 2023 GX w/ only 7K miles and I check my coolant yesterday and it was below L. Added some and seems to be fine. Wonder if its evaporation. Looked underneath and no leaks I could see. Running fine so who know.