I've heard that a contributing factor to XJ radiator failure is due to frame flex causing the radiator to be mechanically fatigued. Has anyone ever considered adding a cross brace to go in front of the radiator to prevent that portion of the frame from flexing? Maybe there is no room?

 

If that's actually an issue seems like a better solution would be to float the radiator... flexible mounting.
Putting anything in there that's going to block airflow to the radiator seems wrong ( I always like the people who mount license plates on the grill)

 

Of all the issues I've had with my XJ, front flex hasn't been one of them - and I do wheel my jeep

 

Best I can say is that there posts where frame flex has been blamed for failure of all-aluminum radiators. I have no personal experience with this. But I do have an all-aluminum radiator.

Floating the radiator would be one way to deal with this. Probably leave the lower mounts as-is, and then set up a squishy rubber donut for the upper mount like I've seen in newer cars.

 

If your concerned with flex in that area several company's make a steering box brace that ties the front end together nicely in that general area.

 

I'm pretty maxed out on bolt-on braces for the front of the vehicle. I have the IronMan4x4 gearbox brace and a custom track bar mount brace. I also have extended bumper mounting flanges that run the length of the steering gear box and have steel steering gearbox spacers on both unibody rails.