OM618, IMO you may have damaged the engine. Every time it is heated beyond it's design point, and especially without circulation to eliminate hot spots and localized boiling, you run the risk of overstressing the metal and the gasketed joint. These engines have some margin for abuse, and I believe you have used up much of that margin. Incipient cracking may have already begun. Fortunately you have an iron head that has much higher fatigue strength than aluminum (and a lower coefficient of thermal expansion). If you had an aluminum head, I think you'd already know the answer because the car would be in the shop getting a new head gasket at minimum and probably a new head. I think you should be extremely conscientious about maintaining normal cooling temperatures from now on, and perhaps the engine will be OK. Wintertime will be an additional stressor, although you live in a mild climate. Good luck!

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1987 W201 190D