Just now I opened the bonnet of a ~8? yr old Avalon to top up the windshield washer reservoir.
As I now know :) idiotically the coolant top-up reservoir and the windshield washer reservoir are right next to each other and look the same!
I put only about a cup of the blue windshield wash in the coolant top-up reservoir.
The coolant top-up reservoir was otherwise, almost full with the usual "pink colored" coolant stuff.
The vehicle is running perfectly, as-new, is perfectly maintained, and never "uses" any coolant even on long runs. (I've never seen the level drop in the coolant top-up reservoir.)
Any thoughts on this?