Erratic heat - not good when you live in Minnesota!

I have a '98 Ford Taurus. Problem is the heater - I do not get hot air blowing unless the car is MOVING! Example: I start car and let it run 5 - 10 minutes before I leave. The defroster (or heater) is blowing cold air and it warms up as I start moving. Now I drive down the road and its blasting nice hot air but there’s a traffic light up ahead. I stop for this light - the air blowing from the vents start to cool down and if the stop is long enough, turns to ice cold fresh air. What is going on? This doesn’t happen with the AC in the summer. The blower works find - I don’t smell antifreeze in the car nor do I see any spots in my driveway, so I don’t think its a heater core issue.

Jeanne533k…what you are describing sounds like low engine coolant. It’s a common problem easily solved by topping off your coolant.

Most newer cars have air blend doors. The heater core is always hot and the blend door varies the mixing of cold/hot air thru the ducts behind dash. Does your car have climate control or manual heat control?

I believe you have a partially plugged heater core. My advice is to go to an independent shop and ask them to flush your heater core. Don’t let them do a chemical flush.
Your temperature control door is electric, so vacuum shouldn’t be an issue for you.
I have fixed many heat/intermittent heat problems by flushing out heater cores. And all of these cars were newer than yours!

Google Ford Taurus brown coolant. These cars are notorious for the coolant getting rusty, and full of brown sediment blocking the cooling system. The rust can also eat away the fins on the water pump Impeller causing the problem you describe.

First, check fluid level. Second, replace thermostat. Third, flush heater core. Then, if all else fails, you will probably have to replace the water pump. Mine was doing the same thing and found out that despite the fact that the water pump wasn’t leaking, it was pumping so poorly that it wouldn’t push enough coolant through the heater core. Once replaced, it heats beautifully now which is very handy in North Dakota.

@ndweekendwarrior this thread is 2-1/2 months old. OP is probably not reading this anymore.