e46 overheating on road trip help please little town mechanic confused

[natvman]

Hello this is my first post ever. I usually work on my 04 e46 at home or if I get stuck my nephew is import mechanic at nice shop. Car was running great and I had my little trailer with harley in tow for trip to tombstone az. Had to manually shift the auto trans to get up onramp past semi. Got on freeway and ac started blowing warm. Saw temp rise to 3/4way so I pullex over and let cool off. Restarted and got off freeway and it rose again. Stopped for an hour than went 1/4mile to hotel. Then cablooey. Towed to shop. Expansion tank blew. 2 days later and $450.00 later it was fixed(outrageous cost I feel). Mechanic came to get me and had to turn around. Same gauge rising issue. Now this is where I am needing advise. What is most likely issue? I am 100% disabled vet living on disability and already am broke from repair and hotel stay. Can not have these guys guessing and costing me my food money. Thank you for any advise. I tried to be detailed and not sound like a dummy.

[tiger5]

If I'm not mistaken, you have the M54b30 engine.. From what a BMW mechanic told me, they have a flaw in design. They tend to get air trapped in the system very easily. I'm willing to bet that's the case. It was an absolute nightmare fixing my e39 530i for the same reason (same engine). What I'm thinking is that your coolant was probably low enough to allow air to be trapped in the system, or a leak in one of the hoses... I had the exact same symptoms. My expansion tank never blew, however.. It could also be your thermostat... But your symptoms remind me of my car, exactly!!! I'm thinking you had trapped air... You'll overheat INSTANTLY! Upon getting a new radiator and expansion tank, I had to bleed the system on an incline (engine angled upwards) because of the air pockets! It sucked... I'm really sorry, bro! Hope this helps!!

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Also, the factory expansion tank is prone to breaking, so maybe you had a crack in it and didn't realize until it was too late.. The system needs to be air tight to work properly.. The more I think about it, the more I feel that trapped air was the problem... Well, keep us posted. Good luck, man.

And thank you for your service brother!! Fellow veteran here!!

[pottsalot]

I'd say tell them to bleed the system the right way. That should take care of all your overheating issues.