I would only put water in an emergency situation where I don't have coolant available. The coolant helps the engine to not overheat and to not freezing, while that could happen if you just use water. If you don't have your vehicle's manual to know the specification of the coolant, you can use the generally available Prestone and add water according to the table on the coolant's recipient. (or you can buy the pre-mixed formula)
Is the question how to bleed a Buick 3800 cooling system? I would say open that little petcock by the themostat housing and release all the air as you fill the system with coolant. When coolant comes out instead of air all the air is out.
Low coolant? Cooling system airbound? Low coolant? Cooling system airbound?
Low coolant? Cooling fan not working? Bad thermostat? Cooling system airbound? Water pump not circulating coolant? Radiator core plugged or restricted? Bad radiator cap?
to check for leaks or in the case of the cooling system preasure cap to raise the boiling point of the coolant
In the cooling system.
Poor coolant circulation in the cooling system.
The coolant will not protect the cooling system against corrosion.
to increase the boiling point of the coolant
To bleed the cooling system on a 1996 Olds Cutlass, locate the bleed valve, which is on the front of the engine above the water pump. After making sure the cooling system is not under pressure, open the valve by turning it counterclockwise. Fill the radiator with coolant until no air comes out the bleed valve, and a stream of coolant begins to flow from there instead. Tighten the valve and close the system to finish the job.
Air can get into the cooling system when the coolant is replaced as either part of a maintenance schedule or when the system must be drained for a repair. When the coolant is replaced the coolant system must be "burped" to get any air out of the coolant lines. There are various ways to do this dependant upon the type of vehicle. A repair manual for your vehicle will describe the proper technique.
to increase the waters boiling point
I believe that the coolant system capacity is 8.6 quarts ( 8.1 liters ) for your Explorer ( if it has air conditioning )