maybe your radiator is broken and you need to get a new one or just get a reparation if the radiator starts leaking when is in use it may be leaking because of the pressure of the water.
It could be water pump, leaky radiator, hoses, head gasket, or just about anywhere else that the coolant circulates. You'll need to get under and find out where it's leaking.
Assuming you mean under the front of the car, the water pump, hoses or radiator could be at fault.
Radiator or hoses. Possible water pump
Could be one or more of several problems.- leaking radiator or hoses, leaking water pump, leaking thermostat gasket, leaking head or intake gasket, leaking or low over-flow reservoir, leaking heater core, radiator drain cock not tight enough, bad radiator cap. Drops or puddles of antifreeze under the vehicle or in the engine compartment or on the carpet under the dashboard (usually passenger side) can often indicate where to look for leaks. White smoke from exhaust sometimes indicates a blown head or intake gasket. In any event, the problem needs to be addressed. It is not normal and leaks of any kind will only get worse over time, potentially bad enough to cause harm to the engine.
Vacuum leak, check your vacuum hoses.
Let me tell basically the places it could be leaking. If it inside the car then the heater core is probably bad. Check the radiator, the top, and bottom coolant hoses. The bottom hose will coming from your water pump. The hoses or the water pump could be leaking (if the pump is leaking then it will have to be replaced). There is a thermostat that could leak if not properly installed. This will be located, under a housing, at the point your top hose enters the engine. There will also be two hoses going toward the fire wall. These are the in and out hoses for the heater core. Theses could also be leaking. You could always get a UV light kit and put dye in the coolant and trace it that way also. (This in my opinion is the easiest method.) Well, I hope you find it. Good luck.
A couple of the most common are leaking cooler hoses and a failed solenoid pack. That is the square thing under where the hoses hook to the trans.
There are hoses, gaskets amd water pump which cause leaking. Check it out where the coolant is comming from.. The speed sensor is probablu bad.
Radiator hoses are located on almost all cars in front of the engine block. One hose on top and on on the bottom. Open your hood and look between the top of the headlights, you should see the first one next to the radiator cap. The bottom one you can see under the car, behind the bumper. They are the largest hoses under the hood.
So far you've done all the right things. Have you considered also having the radiator flushed? Have you replaced the hoses? As the hoses age, they get soft and can collapse when under suction by a properly operating water pump.
your heater core is probably gone
Try to find out where it's coming from. Often coolant will leak down the front of the water pump, under the pulley. Even if you don't see the coolant, look for the mineral trace of the water. By the time you notice a leaky water pump it has usually been leaking for a while and has left a noticeable trail. If you don't notice coolant leaking there, check other places, freeze plugs, the sides of the radiator, radiator and heater hoses... Again, the coolant and water minerals typically leave a nice bright trace to tell you where it's leaking. If the radiator is leaking, don't try to fix it yourself and certainly don't put stop leak or any other chemicals in it. Either replace the radiator or take it to a radiator shop and have THEM repair it properly.