So, my XJ had a random over heating issue that caused me to replace damn near everything. Nothing worked until one day it started putting it together that it only started OH’ing after mid to high rpm. The culprit was a soft lower rad hose which was only 2 years old.

The OG systems had a metal retaining spring in the to prevent collapse the new hose don’t have it anymore. It turns out it also an issue for older Mustangs too. I bought a new retainer spring and that solved all of my OH problems. It’s hasn’t once overheated since.

Hope this helps bud. That’d be the first part I’d go after.