it sounds like you have a leaking heater core
According to the 1997 Lincoln Town Car Owner Guide : ( it came from the factory with antifreeze that meets Ford specification ESE-M97B44-A ) * that would be green color antifreeze *
At the radiator or at the coolant resivoir.
if you can smell antifreeze you need to replace the heater core in the vehicle
look in your owner's manual
For a 1999 Lincoln Navigator : Assuming you want a 50 / 50 mixture of antifreeze and distilled water ( like it was from the factory ) With auxiliary rear heat ( approximately 14 U.S. quarts ) Without auxiliary rear heat ( approximately 13 ) * of antifreeze *
According to the 2001 Lincoln Navigator Owner Guide : It came from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze ( meeting Ford specification ESE-M97B44-A )
According to the 2000 Lincoln LS Owner Guide : It came from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze ( meeting Ford specification ESE-M97B44-A )
According to the 2001 Lincoln LS Owner Guide : They came from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze ( meeting Ford specification ESE-M97B44-A )
If you mean "why", then the answer is that there is a leak in the heater core.
Antifreeze leak top of engine
According to the 2003 Lincoln Aviator Owner Guide : It came from the factory with a 50 / 50 mix of distilled water and YELLOW colored antifreeze ( meeting Ford specification WSS-M97B51-A1 )
According to the 2000 Lincoln Town Car Owner Guide : It came from the factory with a 50 / 50 mix of distilled water and ( GREEN color ) antifreeze ( meeting Ford specification ESE-M97B44-A )