2004 BMW 325xi Q&A
2004 BMW 325xi Question: What could cause the engine to overheat when air is turned on?
You may have air in the cooling system or a bad thermostat. - jrich4344
Being detailed shouldn't be the cause for the overheat. I suspect that you either have a faulty thermostat or faulty water pump. If you coolant was low from a leak somewhere (expansion tank for example), that can also cause overheating. If you recently had any work done, it could also be that there is an air pocket in the cooling system. Running the air conditioner puts extra load on the engine, which can facilitate overheating issues, if something is wrong. - Autohaus Lake Norman