It can happen if the engine gets hot. When I bought my latest 300SD, the PO forgot to mention that he jury rigged the radiator neck that had broke, so when the car got to temp, it would start spewing. The car made it about 25-30 miles before it lost enough coolant to get hot. After I installed a new radiator, I found myself chasing a bunch of cooling system leaks. It started with the bypass hose and then the water pump housing gasket. I got fed up with it, so I replaced all the gaskets, pump and several hoses. THe pump was probably fine but the last person to install it used RTV instead of a paper gasket. I figured if it had to come off, I might as well install a brand new one.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge