Why is my car overheating?

An overheated engine can be caused by anything that decreases the cooling system's ability to absorb, transport and dissipate heat; therefore engines can overheat for a variety of reasons. Let's take a look at some of the most common causes.
Cooling System Leaks
This is the primary cause of engine overheating. Possible leak points include hoses, the radiator, water pump, thermostat housing, heater core, head gasket, freeze plugs, automatic transmission oil cooler, cylinder heads and block. Perform a pressure test. A leak-free system should hold pressure for at least one minute.
Wrong Coolant Concentration
Be sure to use the coolant recommended by your vehicle's manufacturer. The wrong type of coolant and/or mixing the incorrect concentration of coolant and distilled water can also result in engine overheating. The best bet is to perform a complete flush and fill.
Bad Thermostat
A thermostat is a heat-sensitive valve that opens and closes in response to engine temperature. Heated engine coolant passes through to the radiator when the thermostat is in the open position. In the closed position, it prevents the flow of coolant to speed up the warming of a cold engine. When the thermostat gets stuck in the closed position, coolant stays in the engine and quickly becomes overheated, resulting in engine overheating.
Blocked Coolant Passageways
Rust, dirt and sediment can all block or greatly impede the flow of coolant through the cooling system. This can limit the system's ability to control engine temperature, which may result in higher operating temperatures and engine overheating. Once again, a flush and fill is recommended to remove debris.
Faulty Radiator
By passing through a series of tubes and fins, coolant temperature is reduced in the radiator. Leaks and clogging are some of the most common causes of radiator failure. Any disruption in the radiator's function can lead to elevated engine temperature and overheating.
Worn/Burst Hoses
A hose that contains visual cracks or holes, or has burst will result in leaks and disrupt the flow of engine coolant. This can result in overheating.
Bad Radiator Fan
A fan blows air across the radiator fins to assist in reducing the temperature of the coolant. A fan that wobbles, spins freely when the engine is off, or has broken shrouds will not be able to reduce the temperature to proper level, thus possibly resulting in engine overheating.
Loose or Broken Belt
A belt is often the driving link that turns the water pump at the correct speed for proper coolant flow through the cooling system. If a belt is loose or broken, it cannot maintain the proper speed, thus resulting in poor coolant flow and ultimately, engine overheating.
Faulty Water Pump
Known as the 'heart' of the cooling system, the water pump is responsible for pressurizing and propelling engine coolant through the cooling system. Any malfunction of the water pump, including eroded impeller vanes, seepage or wobble in the pump shaft, can prevent adequate coolant flow and result in engine overheating.

sounds like the radiator is blocked either coolant flow or ext air flow through the matrix the thermostat can get ruined when the system overheats so allways change the stat after a overheat problem GET THE RAD CHECKED FIRST if ok check the coolant pump

Needless to say you have not found the right shop yet.
You need to know if the water pump is pushing the coolant thru the system, is the system full of coolant and no air pockets, and is there excessive pressure in the system.
Do the radiator hoses and heater hoses get hot when the engine warms up ?
Are you sure the system is full of coolant ?
Do the radiator hoses swell up when the engine gets hot ?

Could be a sticking thermostat, a restriction in the air flow thru the radiator, a restriction in the coolant flow thru the radiator or block, or other issue.

ENGINE NOT GOING TO START IF GET TOO HOT FIRST THING I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP THEN ADD COOLANT UNTIL COOLANT LEVEL CORRECT THATS WHEN THERMOSTAT OPEN UP AND TOP HOSE HOT.CHECK FOR LEAKING RADIATOR HOSES CHECK TOP RADIATOR HOSE CHECK BOTTOM RADIATOR HOSE.CHECK FOR LEAKS AROUND THE RADIATOR LOOK DOWN BELOW COOLANTS FANS CHECK FOR LEAKS AT RADIATOR CORES OR LEAKS AT THE RADIATOR PLASTIC SIDE CONTAINERS. CHECK FOR LEAKS AT WATER PUMP WEEP HOLE AND CHECK FOR LEAKS AT THE HEATER HOSES AROUND ENGINE BLOCK TO THE HEATER CORE HOSES. THERE IS A REASON CAR OVERHEAT.IF CAR OVERHEAT WHILE DRIVING YOU HAVE FAULTY THERMOSTAT OR LEAKING OUT COOLANT OR BLOWN HEAD GASKET.IF ENGINE OVER HEAT WHILE SITTING DURING A LONG IDLING PERIOD.YOU COULD HAVE FAULTY COOLANT TEMPERATURE SENSOR OR FAULTY COOLING FAN FUSE OR RELAY.HOT WIRE COOLANT TO SEE IF IT RUNS IF NO REPLACE FAN MOTOR. IF YES FAN MOTOR COULD HAVE FAULTY WIRE OR PCM FAILURE. CHECK ENGINE CRANKCASE IF OIL LOOKS LIKE MILK SHAKE ENGINE HEAD GASKET LEAKING.

A split radiator hose will cause the coolant water from your radiator to leak out thus causing your car to overheat and 'die' on you for certain!
DO NOT ATTEMPT TO DRIVE YOUR CAR without a cooling system: with a cooled motor, you need to get this hose fixed and refill your radiator. Also get other engine parts checked as extreme overheating could also cause Cylinder Head and/or Gasket and Engine block cracks.

Does it heat up and overheat very quickly after you start driving , if so , probably thermostat.
If you are driving down the road and the temp is good , then you stop in traffic and car heats up , then probably cooling fan not working.
If it heats up slowly , then just keeps getting hotter till it overheats , then radiator problem.
Is is realy overheating , or is the guage just giving a false reading ?

If you're running it without a thermostat it's clear there isn't enough/any coolant circulating through the block. When the motor is running are the hoses off the radiator soft and flexible or stiff. If they're soft there's no coolant flowing through them. Chances are the radiator core is bad or there is a crack in it somewhere. Have it removed and tested.

The three most likely thing's cause overheating are faulty thermostat,electric fan or clogged radiator. Only at has been overheat so much it boils dry that it will cause engine trouble. Most common problem's are blown cylinder head gasket or a cracked cylinder head.
mixing coolant and water depends on where the gasket has blown or head is cracked. You will first need to check if it actually is overheating. The reason is. If the head is cracked or gasket blown then you can get a false boiling which is compresion from the cylinders blows through the crack in the head or gasket causing the coolant to blow out of the radiator cap.Fill the radiator to the top leave the cap off then start the engine.If the water blows out then you will need to remove the cylinder head check the gasket is ok. If its damaged replace if not get the head checked for crack's. If no water blow's when you start it check the thermostat is working properly. To check the thermostat put it a in a saucepan cover it with water bring the water to the boil. It should open before the water boil's but near boiling-point. If its ok then start the engine again leave it running until it boils and check the fan is running. If that's ok then its radiator problem. Their is no way to check if the radiator is ok you will need to get a new one. One last point. If the cylinder head or gasket are faulty it was caused by overheating so by just fixing the cylinder head problem is not a cure it will overheat again. Check the three things I mentioned at the begining and told you how to check them. Hope this help's. Cheer's

it's either a bad thermostat or a leaking head gasket