It could be any number of things, but here's what to check...
Make sure the radiator is full of coolant (with the engine off and ice cold, facing slightly uphill)
If you need to add coolant start the car (with radiator cap removed) and add coolant while its running directly to the radiator. Once the radiator is full replace the cap then add coolant to the reservoir.
If coolant is not an issue, then make sure the fan is coming on when the car is trying to overheat...a dead fan or bad solenoid to make the fan run is very common on newer cars, older cars used a directly attached fan that always ran with the engine on.
Next thing to check is the termostat, if the car starts to overheat and the top radiator hose is hot and obviously coolant isn't circulating through it then a bad t-stat is to blame.
It could also be a bad water pump; however, under normal circumstances it would leak a small amount of water from a "weep hole", the location of the water pump varies slightly with vehicle.
Lastly you could have a blockage in the radiator requiring repair from a reputable shop or replacement (which is usually cheaper, if you're the one doing it).
Good luck!
might be a bad head gasket or radiator might be clogged or timing might be off you would need a machanic to look at it and diagnose it
most likely you need to replace te heater core.generally i if the leak is on engine you wont smell it in the car
You could be leaking coolant, your blower fan might not be working, etc.
maybe its u or da car
Each car overheats at a different temperature you need to look up and find out on the internet
You might need a new thermostat or heater core.
it sounds like you have a leaking heater core
Give us more info like the year, make and more detail as to what the heater is not doing.
usually it is a vacuumn problem right at the heater control switch or sometime under the hood
YES
You will know of your thermostat is going out when your car overheats, then turn on your heater really hot on full blast, then the temp will instantly drop. This is a sign of a thermostat gone bad.
check your thermostat or your heater core may be getting ready to go out