my 2003 mazda protege has been over heating. Theres no white smoke coming from my tailpipe and my engine oil level is nominal. when it first overheated i looked at the engine for a few minutes and suddenly the coolant(which had gone up well above the fill line) drained out suddenly. it didnt drain onto the ground which i know is a sign of a blown head gasket but ive had no other signs. i let the car cool down drove it till it began to heat again and stopped again to let it cool. i did this three times till i got home. i had someone follow me just in case i couldnt make it. i took it out again the next day after i changed the oil and it did fine for a bit then began to over heat again however the coolant never drained out like it had done before and the engine oil level was still nominal. i let it cool and had someone follow me home again. still no white smoke. could this just be a thermostat issue or something more serious?