My recently purchased 1997 SL500 occasionally shows zero oil pressure on the analog gauge at idle (e.g., at a stop light), but usually the pressure is 1.5 to 2.5 at idle. The oil warning light illuminates properly when I first turn the ignition on, but goes out properly as soon as I start the engine; I have never seen it illuminated while I am driving. Can somebody clarify whether this suggests an oil pump problem? Is the oil pump an electric pump, or a typical mechanical pump that runs off a pulley driven by the serpentine belt. Is the red light an oil level indicator, or a pressure warning indicator?