The crossover is where the coolant flows thru in the front of the intake, and has the thermostat in it. The 96-early 01's had a plastic crossover that is prone to cracking and leaking. When it leaks it shorts out coils, and can do some damage. The fix is the aluminum piece for coolant to flow thru. It was a TSB on all Crown Vics with 4.6's, and any other 4.6 cars with plastic crossovers that started to leak under warranty. ('96-00 Mustang GT's are effected.) Just one of those things.