[mkiv] Oil pressure light

[Oolan Zimmer]

Last night my oil pressure light came on and stayed on.  I immediately
pulled over, checked the oil (level was fine), then started the car, and the
oil light went out.  When I revved the engine to about 2000 RPM, the light
came back on, so I shut the engine down.  Starting the engine again, the oil
light was again out.  I then parked it and got a ride home.

Now, I need to figure out what's wrong.  Checking out the FSM and the
electrical manual, the only thing that causes the light is a pressure switch
mounted on the oil pump.  Either this is an electrical problem that is
causing the oil light to misreport low oil pressure, or something really
funky is going on with the oil pump.

This was a misty wet not-quite-raining night, so it's possible that water
played a role.  Electrical issues don't quite fit, though.  Then again, a
failed fuel pump or an internal oil leak don't fit either.

The only things I can think of are that either there's something in the oil
sump that's getting sucked up against the intake (and shutting down the
engine makes it fall away from the intake until flow picks it up), or
somehow the pressure relief is getting forced open and is then staying open
until the engine is shut down.  A problem inside the pressure switch could
explain things, too.  Does anyone else have any ideas?

The FSM says to remove the pressure switch and connect a pressure gauge in
its place.  I plan on plumbing in a pressure gauge at the remote oil filter,
since I can get to it from the top of the engine.

Oolan Zimmer