Whats this plastic thing? Cool air intake?
 

My 97 xj overheats and vapor locks. Before i do hood vents or a cold air intake from the cowl, was wondering what the plastic rectangle is and if i can remove it or will rain get in behind the headlight. It looks the same size as the opening to the air box and screwed in from the inside.
* and allready double flushed radiator, removed thermostat, and fuel line is wrapped with thermal tape.
https://cimg0.ibsrv.net/gimg/www.che...4fc46d41e3.jpg
the rectangle plastic cover directly infront of the intake box opening

I take that panel out on my cherokees and have no issues but doing so wont change your overheating problem. Want to share more details on how it over heats? Moving, stationary or both. How hot does your XJ get, have you confirmed temp?

You can take it out. A lot of people do. I don't think it will help with your overheating though.

I'll bet your radiator is bad even though you flushed it. Or, your water pump fins may be rusted off. You need a different approach than what you're doing.