You're running the desktop version?
See this FAQ: http://siminnovations.com/wiki/index.php?title=Air_Manager_FAQ#The_EGT_gauge_for_aircraft_X_is_not_displaying_the_correct_value
Not all EGT gauges have a user property setting, you'll need to modify the script a bit. The problem is the same, each developer uses their own EGT values, so there's not one instrument that works for all.