What would cause all the coolent to go into the over flow and cause the car to over heat?

thermostat needs changed..its a mechanical heat valve..

I will assume that your engine is full of coolent, and does not overheat. Now if your car takes like forever to heat up, It will be that your thermostat is stuck open, but after a while, you would have heat in your car. If your engine coolent hoses get hot, but your heater hoses do not, remove the heater hoses where they connect to the engine. This is the first place dirt, grime, and corrossion build up, stopping the flow of hot coolent from going through your heater core. (heater hoses stopped up at engine/waterpump connection.) Your heater core may also be stopped up if there is alot of corrossion present.

The thermostat is located directly under where your upper radiator hose connects to the engine.

Assuming that you have the proper amount of coolent added, check where your heater hoses connect to the engine block for rust and corrossion, this is a common area to clog up, preventing coolent flow from circulating through your heater core.

Assuming that you have the proper amount of coolent added, check where your heater hoses connect to the engine block for rust and corrossion, this is a common area to clog up, preventing coolent flow from circulating through your heater core. If ok, check for a thermostat that is stuck open.

check to make shure there is good air flow thru radiator. could be pluged between radiator and condensor

Possible causes include low coolent level ( I know it sounds wrong, but if the coolent level is low hot coolent won't circulate to the heater core)

The thermostat may be stuck open, if it is the engine won't reach proper operating temp. Only solution is to replace, but it is easy to do and thermostats are inexpensive.

Heater core may be plugged, this is more likely if stopleak has ever been used to stop a radiator leak. Solution would be backflushing the heater core.

The valve that controls the flow of coolent to the heater core could be stuck or defective or the vacuum switch that controls the valve might be defective.

the lower coolant sensor is inside the over flow bottle

disconnect the pipes that feed the heater and join them together with a piece of copper pipe

you can find the coolent lines into the heater through the fire wall disconect them and put pressure through the core to see if its clogged other than that possably a coolent flush cause stuff builds up in the antifreeze and clogs the lines. your heater uses the heat from the engine coolent to heat the air in the heatercore so naturally if you got bad coolent you got heating problems too

Your thermostat will not affect the heat in your car. This is controlled by the heater core which is pulled from coolant from the engine where the coolant will be the hottest. Your thermostat opens and allows the coolant from the engine to circulate into the radiator and the coolant from the radiator flow into the engine. A thermostat is cheap and easy to replace. The sensor should be a fairly inexpensive and easy replacement as well. I would change out the sensor first because bad thermostat would create an overheating problem.