2000 323i weird overheating problem
Here is what I have and what I've done maybe someone here can help. 2000 323I with 99k miles. Car had no heat then ran hot within 10 miles of my house. Had car towed in they put in a new thermostat, rad cap, pressure tested the system and did a chemical test to make sure I didnt hurt the head gasket. Car was fine for about 1 1/2 weeks then had no heat and ran hot again the same distance from my house. I opened the bleeder and filled the system with key on and heater on high. Car ran fine and I checked it when cold for a couple days and topped up the antifreeze. About 2 weeks later same thing happened the same distance from home. I bled it and it was fine until today( about 1 1/2 weeks later) when same thing happened at same distance from my house. I bled it and have been over 300 miles in the car today with no problems. Why am I getting air locked? Could the pump be bad? It always has pressure on it when I open the cap so I dont think I have a leak. Please help this is driving me crazy .