2001 BMW 530, 146,000 miles, Well Maintained, Original owner. Coolant flushed every 4 years as per manual. Pinhole leak near top of expansion tank, can see it bubbling when hot, no overheating problems but need to occasionally top of coolant. should I replace just the expansion tank or should I include the radiator since all is plastic?
Yes, both. And maybe the water pump as well because I think it has a plastic impeller. While you are there, replace the hoses and the thermostat as well. After all, it is 17 years old. These cars will run a long time if you stay on top of cooling leak/failure issues. Any good independent BMW mechanic will know ALL the things that are likely to bite you on these cars.
Thanks for confirming my trusted independent BMW mechanic’s assessment. It is still a great car and was pristine until a couple of weeks age when someone tried to break into my trunk and failed so they carved an X into the paint on the deck lid.