I have a Mazda 626 and it is overheating and when I put water into the radiator it won't fill up

some things to think about..no water leaks RIGHT? thermostate not upside down Have you run a pressure test on the cooling system?.......do you have the right(pound) rad cap. coolant reserve/overflow tank and radiator Full.... ..... maybe a bad sensore and your high speed isn't kicking on all the time.....stuck closed thermostat, a Diagnostic Trouble Code (DTC) can be set......The powertrain control module (PCM) has been programmed to monitor certain cooling system components:...... .. are the fans/fan kicking on...is it worse standing still does it do ut at 50 mph (if not then are your fans working cause you dont need them at 50mph so they say your fans dont matter...anyway is there a code or codes???? all air out of system? a trick is to drill a few little holes in the thermostate as shown...is a rad hose collasping... its 8 years old is the rad fins inside clean... hope theres no bubble (emissions) ( gaskets/crackcoming out of the rad,filler,take it to a shop and have a block checked / head gasket checked to see if exhaust gases are getting into the cooling system. so you wont forget !!!! hummm..time for a break... > If the problem is sensed in a monitored circuit often enough to indicated an actual problem, a DTC is stored. The DTC will be stored in the PCM memory for eventual display to the service technician. It really could be a whole host of different things that can cause a high temp reading. Some things to check for: Is the temperature gauge reading correctly? Is the temperature warning illuminating unnecessarily? Coolant low in coolant reserve/overflow tank and radiator? Check for coolant leaks and repair as necessary. Pressure cap not installed tightly. If cap is loose, boiling point of coolant will be lowered. Poor seals at the radiator cap. Check condition of cap and cap seals. Replace cap if necessary. Check condition of radiator filler neck or degas bottle. If neck is bent or damaged, replace radiator or degas bottle. Coolant level low in radiator but not in coolant reserve/overflow tank. This means the radiator is not drawing coolant from the coolant reserve/overflow tank as the engine cools. Check condition of radiator cap and cap seals. Check condition of radiator filler neck. If neck is bent or damaged, replace radiator. Check condition of the hose from the radiator to the coolant tank. It should fit tight at both ends without any kinks or tears. Replace hose if necessary. Check coolant reserve/overflow tank and tanks hoses for blockage. Incorrect coolant concentration? Coolant not flowing through system. Check for coolant flow at radiator filler neck with some coolant removed, engine warm and thermostat open. Coolant should be observed flowing through radiator. If flow is not observed, determine area of obstruction and repair as necessary. Radiator or A/C condenser fins are dirty or clogged. Remove insects and debris. Radiator core is corroded or plugged. Have radiator re- cored or replaced. Dragging brakes. Check and correct as necessary. Fuel or ignition system problems. Bug screen or cardboard is reducing airflow. Remove bug screen or cardboard. Thermostat partially or completely shut. Check thermostat operation and replace as necessary. Cooling fan(s) not operating properly. Check cooling fan drive operation. Cylinder head gasket leaking. Check for cylinder head gasket leaks. Heater core failure.