Your heater core may have a leak in it, allowing the fumes to invade the inside of the vehicle.
heater core, tough job.take it to a qualified auto technician
if you can smell antifreeze you need to replace the heater core in the vehicle
You need to check for a leak.
According to the 1999 Ford Expedition 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 )
Your gaskets are leaking and you are leaking antifreeze inside the manifold. Same thing happened to me on my silhouette and cutlass. The problem is the orange anti-freeze eats the gaskets. Will cost $2,000-to-$3,000 to fix. Sorry!
heater core....
Usually a heater core problem.
you will smell antifreeze, you may or may not have heat, you could run out of anti freeze
According to the 1999 Ford Expedition 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 ) in the engine cooling system
Look for a valve at the inside bottom of the radiator, often on the left side.
Probably inside the door latch mechanism
The electric fuel pump is inside the fuel tank