I just had a coolant bottle explode.
No excessive pressure, possible prior trauma from an overheat long before I got the car, but has been fine for years now.
I went ahead and replaced the overflow tank and cap just in case, car is running a-ok again, incredibly it blew out in my driveway right as I got home one day.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion