I had a bad over heating problem yesterday. Today I was going to start checking thing out. But , I got lucky that my son came out to help. When he did. He noticed something that I never did and I was so glad that he saw what I didn't. When we went to the store yesterday there were millions of butter flies to and from the store and my radiator was completely blocked with the damn butter flies. So glade my son came out when he did! After flushing out the the radiator fins it is back to normal.
This just goes to say that not always is it a major problem. But, a simple fix.

 

As dinky as the XJ rad is, 2....maybe 3 butterflies, could block it solid.