BMW E39 528i: Cooling System Bleeding Insight
Lesson Learned – Do Not Overfill the Cooling System. I described my experience changing the thermostat housing on my 1997 528i, but I did not describe the problem (a result of my mistake) that followed. As background, all the cars I previously worked on were older, and used a more antiquated cooling system design. “Back in the day”, the cooling system was filled directly into the radiator, and the radiator cap has a pressure relief valve built into it. Excess pressure and (important for this discussion) excess coolant vented from the system through a tube to either the ground or an atmospheric reservoir.
