IMO, it's an old wives tale that the thermostat isnt needed in the Phils.

Without the thermostat the water/coolant runs freely; to the point that your engine may be running too cool then what is intended (meaning it is running out of the optimal temp range). I noticed also that your location is in Baguio city so that would mean your temp there is generally cooler (more meaning for the thermostat then).

Just to clarify: your got better fuel consumption when you had the thermostat installed? When the engine isnt running at the optimal temp range (i.e. cold morning starts) thats when it also consumes more fuel.

Isnt the boiling point of water 100c?