My car has been overheating lately. It doesn't happen while it idles, but during the first 4-6 miles that is has been running. There is also some leaking that I saw under the car after driving it. There are no leaks while the vehicle is idling though. What could be the underlying issue? Thanks.
BMW had a TSB (technical service bulletin) out for a casting flaw where a leak could develop on the lower right side of the cylinder head. Good news though, that was on the M52TU engines and you have an M54 engine, so you are not affected by that bulletin; it’s a good thing because the fix is a new cylinder head.
Common leak areas are under the thermostat housing, and the bottom of the coolant reservoir. Look for a white residue in these areas to see if a leak has developed. If no leak is present in one of these two areas, a cooling system pressure test may need to be performed to locate the leak.
Please note: never open or service the engine cooling system while the system is hot or pressurized or serious injury may occur.
You may want to enlist the help of a mechanic, such as one from YourMechanic, who has the expertise and training to inspect your overheating issue, then locate and repair the cooling system leak, if that is the cause of your issue.