98 Taurus blows cold air after running

I have a 98 Taurus (apx 102000 miles) that yesterday started blowing cold air after it had been running about 10 minutes. I was sitting idol waiting in line at the drive thru on lunch hour. I turned off the heat. When I parked my car I let it set for a few minutes, then turned it back on. Then I had full heat - at all blower settings and changing the temp settings seemed to fluctuate as they should.

Today I had the same problem, after allowing the car to sit idol while waiting in line a couple minutes at the bank, it started blowing cold air. I let it run for about another 5 minutes while driving to see if it would heat up again while I was driving, but never did. When I turned the heat off, and gave it a couple minutes, and turned it back on, I would get hot air, but only for a minute or so before it would blow cool air.

Would appreciate any others with this sort of situation or who has knowledge what it could be. Thank you.

Next time it happens, place car in park and rev the engine up to 1500 to 2000 rpms and see if the heat comes back. If it does, the water pump is probably at fault. However, if the impellers are worn off the water pump, there is also a good chance the heater core may need flushed also. I would go ahead and replace thermostat at the same time repairs are made.

Compare the temp of both hoses going to the heater core. If there is a big difference in temperature between the hoses, I would suspect a clogged or restricted heater core. If the inlet hose on the heater core does not get or stay hot, suspect the water pump.

Thank you for the advice. My husband seemed to think the water level was low, and added water to the engine coolant. It works fine now. It is scheduled for an oil change this week, so I will definitely have them look it over and check out the items you've all noted.

Thanks again for your help - I appreciate it, as I am not well versed with auto mechanics.
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