I got a 2001 es300 coach and the other day I did a little pull and it started smoking like crazy
I drove the other day and it was fine up untill the car was sitting at normal temp then it just kinda did it again
I'm thinking it's the radiator cap because it's such a slight leak it sprays it out but not a lot and it stops the second the car cools. The temp stays cold for a while so it couldn't be the thermostat

 

That's a whole lot of guessing a good way to ruin the engine. Check the radiator for cracks especially the top tank portion. If good fill with Toyota Long Life coolant replace the rad cap with a new OEM part. How many miles, any maintenance history?

 

How much coolant are you losing when the reservoir is filled to the full line?
Radiator cap should be changed every 5 years, however I am going on 12 years with the original and I am finally noticing loss of coolant from my reservoir. I have one on order.
Grab one from autozone, advance or amazon