Every time I change oil in my '90 420SEL, I have the problem of loud rattling upon initial startup from everything being dry of lubrication. The engine parts sound as if they are going to literally swarm for a good three or four seconds at startup. It is scary.

I currently us a MityVac system to extract the oil, but I get the same circumstances if I drain the crankcase in the old-fashioned way. I have even tried cranking the engine several times, and quickly turning the key off before the engine can start with no effect on this problem even when I crank a dozen or so times or more.

Two questions, really: What is the underlying cause of this other than the obvious of dry bearings and oil pump, in other words is this some engineering or design flaw? Does anyone make a pre-oiler that can be installed on the engine in order to get a little lubing happening prior to startup? I've seen pre-oilers on some RV's. I'd appreciate any help as I can just imagine the damage these dry starts are causing my engine. TIA.

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1980 300SD 146K miles.