you must put distilled water in there if you choose to put water. remember it is important to put a 50/50 mix of coolant and water because the coolant raises the boiling point of the water. if you just put water, it will boil too quick and may lead to damage.

also, the thermostat does not activate your cars cooling fans(it has no electrical connections). it is a mechanical part that allows the coolant to flow through the engine once the coolant has reached a certain temperature. you must test your fan switch.

you should get your hands on a HELMS manual. it has a flow chart on what to test. i would start with these items first: cooling fan relay, condenser fan relay, fan switch, and make sure they are getting the necessary voltage(refer to service manual for what pins should carry what voltage).