My 2000 XJ8 has started overheating when stopped for a few minutes in traffic. Once I start moving again at a steady speed, the temperature lowers to normal. I have already tried having the radiator flushed and refilled with new antifreeze.

 

The easiest test is start it, Push the climate control panel down again and again until the screen says LOW. and then turn the fan control knob for max fan.
Now is the electric fans running like the are trying to cool the desert. If yes shut down the AC. If no then the fan controller or the fans themselves have quit working.
Next let it sit and idle to warm up do the fans come on and shut off. If yes then get the systems flushed and refilled. If no then back to bad fans or controller.
12 volts can be applied to the fans to see if they run and if they do that would point to the controller.

I just realized the error of my ways check fuse 12 in the engine compartment fuse box it powers the fans. Duh simplest first.

 

Hey Vern, what about the plastic water pump veins?

 

Highhorse, that is a possibility but I always like to start with the easy checks first.If all of the checks show the fans good then it on to the thermostat and pump.