Ben2017 there is a general concensus that while they will reduce underhood temps they won't make a noticeable difference in engine temps. Here is a discussion on different installs for the XJ.
http://www.naxja.org/forum/showthread.php?s=&threadid=6298&highlight=hood+vents
and another...
The hood louvers on the 98 Jeep Grand Cherokee 5.9L are not thermostacically controlled. They consist of two parts a louver and water shield tray. Here is an article describing them.
January 19, 1998 Design News
Patented part adds more zip to Jeep engine
Detroit--At a quick glance, buyers...
