BMW Repair: Heating, coolant leak, 525i bmw

Question
I have a 1991 525i bmw and it's been overheating. When i drive it's fine but when i idle it starts to overheat. I've tried bleeding the system without any luck. I think i have a heater core leak. Will this cause the system to overheat? I just had the raditor replaced and it ran fine but due the the heater core leak i've added antifreeze here and there. Wondering if this could cause the system to overheat. Any advise would be greatly appriciated.

Answer
Bryan any coolant leak can potentially cause an overheat because the system isn't allowed to pressurize, thus not raising the boiling point of the coolant. If you have a pin hole leak in your heater core it is unlikely that this is the cause. I always replace the thermostat after an overheat as the internal wax pellet can be damaged. Phil if it is over heating at idle I would look toward the fan clutch and the electric fan if equipped. Make sure those are comming on when the vehicle is up to temp. and staitionary. It is their job to move air over the radiator when there is no ram air flow. Make sure your radiator cap is good also. Pressure test the system and look for any other leaks.
-Evan