when you drain/fill any cooling system, the coolant will always drop a bit after the first ride around. They topped it off and it dropped due to the engine cyling the coolant. Top it off one last time and it'll stay full this time. you dont need to bleed the system, but you do need to burp it. fill it up and pinch the middle of the upper radiator hose, this removes air pockets from the system.
1998 Mustang GT
MAC CAI, MAC O/R H PIPE, FLOWMASTER 40's, BLUE FRPP 9MM WIRES, TRICK FLOW 75MM UPPER PLENUM, 73MM TB, BBK STRUT TOWER BRACE, HURST PISTOL GRIP, WHITE FACED GAUGES, MATCHING SPEEDHUT OIL PRESS. AND WATER TEMP. GAUGES IN A FRPP DUAL POD A-PILLAR, BILSTEIN STRUTS, KONI SHOCKS, H&R SUPERSPORT SPRINGS, DNA REAR UPPER/LOWER CONTROL ARMS, 18'' CHROME Y2K'S, MICHELIN 295/35 AND 275/40 PILOT SPORTS, KENWOOD HEAD UNIT, PLANET AUDIO 1000W AMP AND 10" MEMPHIS SUB :nogrinner