[net.auto] Rabbit/GTI oil pressure sensor

seifert@ihuxl.UUCP (D.A. Seifert) (08/19/84)

This is being posted for Joe Pokorny, who's machine gets mail, but not news.

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>    The oil pressure light in my GTI has been coming on for a couple of
> weeks now, accompanied by it's incredibly nasty buzzer when above 2000 rpm.
> The problem only happens when it's humid or wet outside, and only lasts
> until the engine warms up.  There's no valve clatter or other noise to
> indicate a real problem, though at times it seems the oil temperature is a
> couple of degrees higher than normal.  (That may be due to the fact that I
> normally don't pay much attention to the oil temp, and don't know what
> "normal" fluctuation might be.....) 
>    The dealer checked all the pressures, etc. and said they were fine (of
> course).  Is this similar to your problem?  If not, has anyone out there
> had trouble like this?  Any recommendations? 

If you haven't had the "how-it-works" talk on Rabbit oil lights, here's a
brief synopsis:

1982 and later Rabbits and other VWs have a dual sensing oil idiot light.
Below 2K rpm the standard 2.1-6.4 psi normally closed (no pressure) sensor
mounted on the head (driver's side) is monitored by an electronic relay module
on the fuse block.
Above 2K, the module detects the higher revs and switches to a second sensor
which is normally open, set for 23-29 psi, and mounted on the oil filter
casting.
This provides sensing of high enough pressure at running speeds without
false indications at idle.

Your problem seems to be associated with the second sensor because it fails
at above 2K revs and thin oil is out because it passes hot.

When its in a failing mood, try grounding the lead to the top of the sensor
mounted on the oil filter casting while the engine is above 2K revs (it
may require a helper/observer); if the light/buzzer go off, the sensor is
sticking open--replace it. If not, the wiring or module are probably at fault.
I'm surprized your dealer didn't check for this but then again I've had
some bad experiences with incapable repairpersons at dealers.
If you don't have one, buy yourself the Bentley manual available at the
dealer or some bookstores. All of this info and a lot more is in there
but unfortunately not error free.

Good Luck

Joe Pokorny (ihnp4!nwuxc!pokorny)

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