I had most of the coolant system replaced and continues to over heat? Any ideas?

What is your question?

Radiator, water pump, thermostat 2x, and expansion tank replaced. Last mechanic said they think it’s the cylinder heads being warped but they didn’t take them off to check. That being said they don’t like working on bmws anyhow. Bought a 88c thermostat to help it run cooler hope it works. No leaks visible, oil seems fine and no smoke out the exhaust. Temp gauge will go up and down for a little bit then will begin to over heat after wards

What makes this problem better or worse?

Happens after 15 minutes of driving

How long has your 2003 BMW 540i had this problem?

A couple months