oil warning Light

[rocketroy]

Was driving my 91 8v in to town in slow stop start traffic. After about ten mins the oil warning light started to flash. I parked up strait away and when I got back to the car after 30 min and started it up the light had gone out.
Checked the oil when I got back and it was up to level. The car drives fine on normal roads and water temp is where it should be.
Any ideas?

[Santiago]

How long since the oil was changed?

If it's been a while that's the first thing I'd do.

If it comes on again after that, I'd be considering dropping the sump to get a look at the oil pick-up strainer.  Could be that it is partially blocked and needs a good clean out.

[The Mighty Elvi]

The warning is for Oil pressure, not oil level.

[rocketroy]

Its been a little bit since the oil was changed so that will be the first job.
Would oil pressure dropping be consistent with what is mentioned above or a sign of another problem?

[Diamond Hell]

Change the oil, as suggested.  It may be you have the wrong grade of oil in there - it warms up, thins out and the pressure goes.

If when you've done that, the warning is still there, drop the sump.  Also check what the sensors on the engine are and make sure they're the correct ones for the motor - wrong ones will alarm at lower pressures than correct.  The part number is on the underside when you remove them.

[rumlad]

Yep, mine was doing this too, oil light flashing when engine warmed up in slow traffic.

First thing I did was change the low pressure oil switch on the side of the head for a proper blue VW one and problem solved. Try this first. 

[clipperjay]

If all of that fails drop the sump clean/inspect the strainer its like a domed mesh that sits in the pick up sometimes they get clogged and suffer pressure drop and feed to the head!

[djfox]

Oh ok so if the strainer is clogged the head won't get oil?

[clipperjay]

Oh ok so if the strainer is clogged the head won't get oil?

Yes but the pump could be finished as well hard to speculate unless you check it after all senders have been switched out prior!

[Santiago]

Oh ok so if the strainer is clogged the head won't get oil?

The whole engine - not just the head - will get lower pressure oil if the strainer is significantly blocked.  Head may give the first symptom though; your engine has hydraulic valve lifters, which tend to get noisy/tappy quite early if the oil pressure drops from what is needed.

Check the pressure switches for oil leakage (which probably indicates internal failure) but I'd say if either had failed completely you'd have a constant warning light rather than one that comes and goes.  Partial failure I guess could occur?
The blue switch that has superceded the brown one has marginally lower threshold, 0.25 bar rather than 0.3 IIRC, so swapping that out and 'fixing' the warning light may be a false sense of security.  Unless the old switch really was faulty of course.