You won't find a separate "heater intake tube" sticking out somewhere. The coolant flows from the engine block, through a hose to the heater core (located behind the dashboard), then back to the engine. The "intake" is the hose that carries hot coolant *into* the heater core from the engine. This hose is usually located somewhere near the firewall, and is generally connected to a fitting on the engine's water manifold or a specific heater supply hose that originates near the engine. It's difficult to give a precise location without being able to see the specific engine bay.
To find it, you'll need to:
1. Consult a repair manual: A Haynes or Chilton manual specific to your 2003 Ford Windstar will show diagrams of the cooling system, including the heater core hoses. This is the best way to pinpoint the location.
2. Look near the firewall: The heater core is behind the dashboard, close to the firewall. The hoses connecting to it will be routed through the firewall, often near the bottom.
3. Trace the hoses: Follow the coolant hoses from the engine. One of them will lead to the heater core. The hose going *into* the heater core is the intake.
Caution: Working on the cooling system involves hot coolant. Let the engine cool completely before attempting any work. Also, be prepared for some disassembly (possibly trim removal) to access parts of the system, especially near the firewall.
