1997 Ford Expedition Low heat

Before doing that, lets check something. With the engine warm, rinning, and the heater on high, feel both heater core hoses. Both should be hot. If they are, there isn't a problem with the heater core.

Let me know what you find.

You shouldn't need to cover the radiator. If both hoses are hot, then the heater core is okay and not plugged. What I would think is the problem is called the "Blend Door". It is a vent door that directs air through the heater core box so hot air enters the vehicle. It is located near the heater core and not easy to get to. THat is what I would check. As far as flushing the heater core, if you would have said one hose was hot and the other cool, then I would have recommended the flush. However, I feel strongly that isn't the problem and it's related to the blend door. I hate to say it but I would suggest taking it to a shop to have the blend door checked unless you really feel confident that you can do it. It can be quite a job.

It's been awhile since I did one, but I think you need to remove a good portion of it.