Oil Pressure problems, on my 87 190D I just started to experience a drop in oil pressure at highway speeds while underway for at least 10 minutes. The gage on suddenly starts to creep from the normal 3 reading through the two's and to zero, and subsequent to zero the oil warning light also illuminates. The first time this occurred I stopped, and checked the oil, which was reading full. When I re-started the car the oil pressure went back to the normal 3 range. However, on the highway on the way back the same thing occurred. Is this indicative of the sending unit in the sump going bad, the sending unit on the side of the oil filter housing, or pump failure. The oil and filter are changed religiously at 3000 mile interval. Owned car for last 100K miles and never seen a oil pressure problem.

87 190D 203,000
87 300SDL 119,400
99 F350 Super Duty