97 Honda civic dx.. commuter vehicle.. 283k on it. Temp gauge normally runs just under half way up any driving conditions. Recently started heating up after freeway driving when I come to a stop. Put in neutral and rev engine, it cools off. I waited until it cooled and radiator was low. No leaks anywhere. I have changed the radiator cap, thermostat, and coolant recovery system. What it does is when it heats up freeway driving it transfers antifreeze into the overflow tank. It just sits there and doesn't transfer back and overheats. When it cools for a couple of hours, (engine off) I take antifreeze from the overflow and fill the radiator with it. It runs normally freeway driving until I have to come to a stop and the cycle repeats. No smells or obvious head gasket leaks, no steam out of the tail pipe. I am at a loss.. cooling fan comes on just fine. Did I mention no leaks noted? :( any input would be greatly appreciated.

This link should help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post235973

The radiator may need replacing due to phosphate scale buildup.

I've lived in areas with extremely hard water such as Arizona and had never thought about minerals and boiling thus plugging a radiator. visual through the radiator cap does not show me that this radiator is scaled or anything. Should I be looking at something else?

My bet is the radiator is bad. Take it to a radiator specialty shop, if you have doubts.

Radiator could be bad or the thermostat is sticking... much cheaper fix so I would check thermostat first