no heat

help,if any one can tell me what to look for in correcting this problem,fist off i am getting no heat,and my engine light is on,plus i have had to put antifrezze twice in the last 3 weeks,but overflow tank is ok now no leaks that i can find and trust me i,m been looking closely,no indacation of coolent in oil engine is running very well.
any help would be greatly needed thank you
thanks all problem was fixed was the therm after all

First Of Check The Code Of The Check Engine Light, If You Need To Put Coolant In, Then Its Going Out Some Where Else, Is Your Floor Damp? Is Their A Sweet Smell Of Coolant In Your Cabin? If So U Have A Heater Core Leak, If Not, Im Not Surprised U Have A Slight Headgasket Problem, Do U Have Heat In The Rear Of The Vehicle? The Overflow Tank Will Not Always Go Empty, Only If A Vacuum Is Created In The Cooling System Sucking It Back In...good Look
Ford Tech

Water Pump
I just went through the same thing, no engine light though. Bought it in Ohio and drove it home to Ontario (500 miles) without any problems, but no heat, and it would always take some coolant when I checked it (overflow was always fine). Traced it to the water pump. All the vanes were off and the impeller was like a flat washer. The leakage (that I could never find) as far as I can tell was small, and around the tube that comes out of the water pump going to the heater hose. It was rusted out around the o-ring.

Fisherman,

What year is the Windstar?

SOHCFreak makes a lot of good points:

1) Get the codes read
2) The coolant is going somewhere.
3) Does the temperature of the engine indicate a problem?