1997 Ford Aerostar

Heater problem
1997 Ford Aerostar 6 cyl Two Wheel Drive Automatic 86000 miles

Only mild heat from front and rear heaters when fan set to low. Air goes cold on higher fan speeds. Replaced water pump and thermostat last night. Same as before. Controls seem to work normally. Fresh coolant. Well maintained van. Could bad heater bypass valve affect both front and rear systems?Could too much cold outdoor air be entering somewhere?It's cold here in Chicago!

Thanks. Jim
January 8, 2010.

Sounds more like restricted heater cores.

What do the heater hoses feel like at the heater cores? Hot to the touch, same temp?

Both heater core lines are hot and bypass valves working properly. Seems like too much cold outdoor air entering both systems. What should I check. I am very mechanically able. Very frustrated. Jim

Jan 9, 2010.
Okay good.
Lets look at the probablity of air pockets. I think you have a stubborn one. Raise the front of the van up 3+ feet or as high as you can get it. Add coolant a few ounces at a time. Keep reving up engine, lettling it come back to idle. May take 50 times of this slow procedure.

There is a tool that snap on makes. Prolly others too that attaches to the rad and puts a vacuum on the system to pull the air out. The aerostar can be a real stubborn one to bleed. The engineers didn't worry about that when they built it. I'm pretty confident that you'll nail this thing if you get the air out.

Car just seemed to be taking in only cold outside air and overpowering heater cores. Removed outdide grill that runs accross bottom of windshield and along hood. Removed and found fresh air intake opening. Sealed hole by compressing large sponge and inserting into opening. Front heat now working at about 80% of normal which is pretty good. Rear air still same(slightly warm at low air speed)Does rear air have fresh air intake also? Sounds like a damper/s issue. Any ideas. Cannot find any diagrams of ventilation or heat controls. Jim

Jan 9, 2010.
I still think there is an air pocket in the cores.

Remarkable how much the temp came back for you by blocking off the air intake duct.

I'll look for the info you requested and update when I do.