Re: Oil Warning Buzzer - Possible Causes (Oil Pump, Oil Filter, Vacuum?)

[BJohn77777@aol.com]

In a message dated 96-10-07 17:12:09 EDT, you write:

<< I recently started having my oil warning light/buzzer going off again in
 my Audi 4000SQ.  The first time it happened was a year ago, after not
 driving it for months.  (Out of town.)  I changed the oil and everything
 has been fine - UNTIL NOW.
 
 
 It buzzes for about 5 seconds, then goes away.  It usually happens when
 the car is colder, and only every 3-4 times I drive it.  It will occur up
 to 5 times within a 30 minute period.
 
 I have opened the oil cap with the engine running, and see oil splashing
 around in there.  My oil stick shows full.  Tried changing the oil w/ 5
 quarts of 10W30 and a new filter.  Still have the problem.
 
 Am I correct that the buzzer goes off due to low oil pressure?
 
 My unknowledgeable guesses as to possible causes:
 
 1) Oil pump going bad - but Linda @ Carlsen claims this almost NEVER goes
 bad.  It's also $320.

Last resort!$!$!$
 
 2) Oil filter causing too much resistance - I use filters with the
 anti-backflow valve (Bosch, AC Delco) - Should I try a Fram, which does
 not appear to have the valve?

Ummmm..idon'tthinkso...
 
 3) Oil pressure detector malfunction - Some of my vacuum lines are old.
 Can this be the cause?  Does the oil pressure check even use vacuum lines?

Oil pressure control unit...good possibility...yet still$$$$ Vac lines
totally irrelevant...not even...
 
 Any suggestions?

John,

Buy a cheapy direct reading oil pressure gauge at you friendly auto parts
store (with proper metric adapters).  Remove one of the two oil pressure
switches and insert the gauge in its place.  Start engine and observe OP.  Is
it good?  Above 2k rpm @ oil temp of 80 deg C pressure should be minimum of
28.4 psi

The dynamic oil pressure circuit uses two oil pressure switches, a .3 bar and
a 1.8 bar switch.  These work together to indicate some very basic engine oil
pressure parameters.  The .3 bar is used for low speed/low oil pressure
indications.  At idle if pressure drops below .3 bar (4.3 psi) the oil
pressure light will illuminate.  Some vehicles this would show up as a
flickerig of the light after a high speed run and then coming to a stop (i.e.
freeway off ramp).  Considered normal (arrgh...) according to some owners
manuals.  Theother switch is probably the more crucial one.  It will cause
the oil light AND warning buzzer to come on if oil pressure drops below 1.8
bar (26 psi)  and engine speed is above ~2150 rpm.  The . 3 bar switch is
normally closed at 0 psi and opens at .3 bar,  The 1.8 bar is normally open
until ~1.8 bar is reached, when it will close.  I would buy a gauge and test
the system and switches (least expensive way to verify) vs changing expensive
engine oil pressure control units, oil pumps, etc unnecessarily.  If you need
help checking the switches with this setup let me know and I'll walk you thru
it...
 
 Thanks (yet again) guys!

r plezur...
 

Bruce Johnson
85 4Ksq
Olympia, WA