My 2000 RX300 literally started overheating all at once, as in pegging the guage and boiling the coolant. I have had no other issues with it so far. It has 178,000 miles and I have had it since 100,000. Top hose was HOT and bottom was cool/warm so I thought thermostat. I have pulled the thermostat and it looks fine. I boiled a pan of water and it seems to be openng fine, at least as well as the crappy new one from the parts store does, about 1/4" gap. I am not sure that this is my problem. I have mechanical experience, but mostly on older American cars, still learning on the newer foreign cars.
I am looking for common issues on the 3.0 VVT engine first. The water pump is a pain, and the radiator is expensive. I am assuming this is a reverse flow system(in the bottom out the top of the radiator)?