The composite (plastic) intake manifold may crack near the thermostat housing and cause a coolant leak. Ford released an updated manifold that was reinforced to prevent a recurrence. No recall was issued for this problem but Ford did extend the warranty to seven years on some models from the date of purchase.
2003 Ford Crown Victoria Problem Reports
Most Reported 2003 Ford Crown Victoria Problem Reports
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Catalytic converter failure is common. Internal components become loose, causing a rattle or creating back pressure in the exhaust.