Last year I posted 4 articles in which I detailed some inexpensive steps I took to get my car running : https://steemit.com/cars/@pinkspectre/diy-auto-repairs-saved-me-thousands-part-1
https://steemit.com/cars/@pinkspectre/diy-auto-repairs-saved-me-thousands-part-2
https://steemit.com/cars/@pinkspectre/diy-auto-repairs-saved-me-thousands-part-3
https://steemit.com/cars/@pinkspectre/diy-auto-repairs-saved-me-thousands-part-4
Here it is a year later, and the same vehicle was starting to overheat again! I flushed out the system and added KSeal again, just like I did last time, but the problem was not fixed. The intake hose at the top of the radiator was getting hot as it should, but the outflow hose at the bottom was remaining cool, indicating that fluid was not flowing. (Incidentally, although a laser thermometer can be picked up very inexpensively now-days, it isn't necessary for this diagnostic, as you can easily feel the temperature difference in the hoses with your hands after only a few minutes of starting the engine.)
I figured the next place to look at would be the thermostat (about $30), and if a new one didn't fix it I'd have to change the water pump. But I happened to read that the radiator cap has to keep the system to a specific pressure, and if the mechanism fails, it can throw off the whole works.
So for 10 bucks, I picked up a new one at the auto parts store. And that fixed it. Boom! Problem solved. The old cap had failed and wasn't keeping the pressure in the system. I'm so glad I tried this before taking out half the front end to get to the thermostat, which is totally buried in my 2001 GMC Envoy.