Over heating

If my thermostat isn't responding right wat will be the side effect

Check the thermostat housing on the top of the engine, it's black, made of plastic, and has a radiator hose connected to it. Visually look to see if you have any water on or around it. They tend to develop small cracks around the joints. When the begin to leak, the water runs on top of the engine and usually evaporates off due to the head of the engine before it hits the ground. Is the plastic tank on the passenger side of the engine compartment empty or severely low? Does the fan blade turn when the engine is running? Has the coolant ever been completely changed since 2002? Never add plain water to a vehicle radiator.