1998 Honda Civic Overheats?

Ive had 3+ Honda civics and they have all overheated at some point. I have a 1998 Civic DX and it is overheating again after replacing the engine... It started about 1 year after installing the engine... The car overheats when driving but if its cold and its idle, no overheating. Also, when I drive the car and it begins to overheat I turn on the Heater and it stops overheating. I can drive for 100 miles with no problem but with the Heater on. Once i turn it off, after about 30 seconds or so it starts to heat up again. I removed the thermostat prior to this. SO the only way it stops overheating is when i keep the heater on full blast... Also, if i dont turn on the heater, the coolant will flow through the resorvior and eventually have no water in the radiator, but when the car cools off the resorvior tank is empy and i still have to add water... Now, if i keep the heater on, the water is constant... no leaks, no missing water.. just overheats when the heater is not on. Antifreeze is 50/50 maybe more antifreeze than water. Bought a new radiator today and will put it on.. can anyone tell me what is going on? Thanks in advance