Oil Warning buzzer

[LCSCHADT@aol.com]

Phillip,

In your recent posting you wrote:

>this time the oil light comes on and the buzzer sounds, at random times.  if
i press in >the clutch to drop rpm's below 2k the buzzer and light stop and
usually do not occur 
>again for days (weeks!)  each time i check the oil and it is ok.

>... i have thought that it might be the sensor, but the mechanic i use says 
>it tests ok.  has anyone else had a similar problem?

Intermittant problems can be a bear to figure out....

Your experience that the warning lite/buzzer go off once RPM drop below 2k
indicate that the low pressure oil switch (.3 bar) is not part of the
problem.  That leaves the high pressure switch (1.8 bar), or the circuit
board/buzzer that monitors the two switches and engine RPM.  (oil pressure
below 2,000 RPM can be below 2 bar, and be acceptable, but the high pressure
switch closes - the "computer" knows to ignore the high pressure switch if
RPM are < 2k - the low pressure switch is reacted to if the engine is
running).

Similar problems in an '82 jetta, turned out to be the little on-board
circuit board/buzzer.
 
However, despite your mechanics reassurances, it could be that the 2 bar
pressure switch IS malfunctioning intermittantly, and closing to ground (and
completing the circuit) even when the pressure IS above 2 bar.  I believe a
posting a couple of weeks back suggest that the circuit board is ~$150 item
-PLUS LABOR (the jettas was ~$115 in '87).  The pressure switch I think about
$15 (as a matter of fact, I may have the one we tried replacing on my
daughter's jetta.... to see if it would fix the problem before forking out
the $115 for parts).

At ~$15, (and little labor) it might be worth replacing the the 2 bar oil
pressure switch, which on my 5kSQ is mounted on the driver's side of the
engine between 2nd/3rd cyl, with the WHITE wire (don't know about your '86
coupe).  It's down under the power steering pump, looks like a large bolt
(about 25mm head) with a wire coming out of it.  It could also be a problem
with that wire grounding somewhere.

Alternatively, you could simply disconnect that wire for a week or so, tape
it up out of the way so that it doesn't ground to anything (and thus set off
the low oil pressure buzzer/lite).  If the problem goes away, and then
returns when you hook it back up, then you can be pretty sure its that oil
pressure switch.  DANGER WITH THIS APPROACH... if its not the switch, and it
IS THE OIL PRESSURE you could get into some trouble....  There is a second
switch (.3 bar - located near the other swich, this has a brown wire) though
should warn you about a catastrophic failure, and would still work while the
other was disconnected (and would continue to show the warning light even
after RPM below 2000).

There is also a small instrument voltage regulator which can malfunction and
cause the oil pressure computer to malfunction...and I image there are others
resons such as the faulty ground that you suggest.

Good Luck,

Larry  '87 5kCQ (formerly '69 bug, '66 912, '82 & '85 jettas)

In the event you decide to replace the 1.8 bar switch, I suspect it is
standard VW/Audi fair.