After I flushed the radiator and filled it with fresh coolant (50% mix) up to the optimum level in the reservoir "low coolant" light comes on when I drive the car. The engine does not over heat, there is no leak, and the coolant level in the reservoir is at mid point between the low and high levels, but the "low coolant" light still comes on. Could it be that the coolant has not circulated through out the system, particularly up to the point where the coolant level sensor is located, and will it correct itself after some time. Thanks for any insights on this.
You need to squeeze the radiator hoses to remove the air from the cooling system after filling. While the engine is cold, just reach down and squeeze both radiator hoses separately, but along their entire length. You will hear bubbles, repeat until you no longer hear bubbles. Some people call this "burping the system."
The 3rd-gen Taurus doesn't have bleeder screws like most engines and instad relies on the coolant reservoir, also called the "degasser", to purge air from the system. Basically, fill the reservoir to the brim and idle with the reservoir cap off until air stops bubbling up. This should be done after burping the system, and beware of the mess this may make, idling without the reservoir cap and all.
Here's 2 links where I got this info from: