The nx200 (2017) intercooler cooling system is a separate cooling system, with its own drain and overflow/refill tank.
Changing the coolant

Finding the petcock to drain the coolant is the most difficult part, it's barely visible. You cannot see it from the top, and even with the lower shield off, it's barely visible from below. But you can feel it.
To find it:

No need to jack the car up.

Get underneath.

Lie on the floor, face up.

Raise your hand, and move your hand forward over the steel cross beam just to the rear of the radiator. You'll feel the rubber hose, maybe one inch diameter (or maybe 1.5 inches?) It runs transversely, just rear of the radiator, about a few inches above the radiator bottom. Slide your had back and forth along the hose, you’ll feel a couple of hose supports, and moving your hand along the hose towards the right side of the vehicle, you can feel the petcock inline with that hose .
The petcock works by partly unscrewing the petcock handle, which is located on its bottom, under the hose, and you unscrew it using your fingers on the two small ears at its bottom. No tools needed. Don't remove it, since as soon as it’s loose enough, you’ll feel the coolant dripping down your arm, it only takes a turn or two. And it might be hard to get it back in since you can't see it.
To refill (3 qts total) you need to open the bleeder on the far right side of the top of the radiator. See pictures.

There is a 6 mm hex recess in the handle; you can see the hex wrench in that recess in the close up pic. Hold the hex wrench horizontal and enter the handle from the front of the car into the handle, and you unscrew a couple of turns. Don’t remove it either.
After those two are found and opened, the rest is straightforward
Lexus asks you to turn the electric pump on a few times via a scan tool, but just drive it a bit and after each heat-cool cycle the bubbles will rise and you just keep refilling the overflow tank

 

I did this last year - I maintain my sister’s 2015 NX200t. I did spot that intercooler drain valve and it was a PITA to access. I didn't know about that bleeder valve on the radiator. I did find a different bleeder screw on the block, where they are normally found. On the NX it is right next to the oil dip stick. And I also found out later there is another one. See link below. And, as I always do, I flushed out the Toyota coolant with distilled water and replaced with green universal coolant.
https://www.clublexus.com/forums/mai...tor-flush.html

 

At what mileage/duration do you recommend flushing/filling the intercooler?