'97 Vectra B 2.5 V6 oil light coming on

Hey guys, have been mucking around with this very same Vectra B with the 2.5 54deg V6 (at least it's 5spd manual.) which has been the bain of my existence for the last 6+ months. It first came to me with a sheared off cam-shaft dowel pin after a reputable workshop here in Hamilton had replaced the cambelt (and seals) not long before hand and musn't have torqued up the camshaft sprocket bolt tight enough. Anyway after it had been sitting for a while after the engine lunched itself, I replaced the front bank cylinder head (and torquing the camshaft sprocket bolts up tight enough), refitted a new cambelt and tensioners etc and got it running.

While taking it on its maiden voyage for the first time since 2008, the oil light started flickering on ever so slightly and as you drove along further it eventually turned on more or less solid. The flickering doesn't seem to correspond with engine revs or anything else. The oil was still full and there were no leaks etc. After getting it back to the garage and letting it sit for about an hour the light did not come on after the re-start and even after letting it idle for 15-20 mins, but would come on shortly after when taking it for a drive.

After having experience with a similar symptom on a Vectra A 2.0 4cyl which ended up being the oil relief valve dirty and sticking open, we decided to set about removing the oil relief valve on the V6. However Opel in their infinite wisdom made it that you needed to remove the cambelt and tensioners to do so, and the torx drive it requires only sits into the hole about 2-3mm. Needless to say, the head/cap got munted when attempting to undo it. It looks like the oil pump needs to be removed in order to get the oil pump in the vice and the oil relief valve cap removed easier on the bench - however to remove the oil pump the job requires you to remove the sump pan, the alternator, all four camshaft sprockets and the steel backing plate behind the camshaft sprockets - basically not a fun job at all!

My question is, has anyone else out there experienced the same issue with a Vectra V6 and happened to fix the fault without the removal of the oil pump and oil relief valve! We've flushed the oil out once so far, using oil flush and letting it idle for 30 mins and refilling with fresh oil - the oil which came out of it (1 hour old 15W40) was still clean as a whistle when drained.

Any ideas! Not looking forward to removing the oil pump.

Check oil pick up. If it was sitting for a while oil pick up may be blocked. simple things first.

Sounds like cavitation.

I'm not trying to sound like I'm a rough c.t, but have you tried using Morey's oil stabiliser additive!

Mmm, have you actually tried plumbing in a guage and really seeing what oil pressure it actually has!

We've switched to 20W50 after the oil flush which made the engine alot quieter in the top end, but after still driving it, the oil light comes on. Basically oil pressure is strong until the revs/pressure get up enough to open the oil relief valve, and once it's open it sticks open only closing again when the engine has been cooled down over time.

No we haven't fitted a gauge due to Opels using such a weird thread which would require buying an expensive adapter. We have however tried multiple oil pressure switches including a brand new one and the result is exactly the same. Leaving the oil pressure switch unplugged results in no oil light whatsoever and after taking it for a drive with it unplugged the oil light doesn't flash once - so I don't think it's a wiring fault, and we're fairly certain the oil pressure switch is definitely seeing low oil pressure.

I had the same problem on a slightly later model V6 Opel - it was the oil sender in the sump of all things (had to remove sump to replace the unit) wasnt cheap ex OZ but it sounds similar, this was not oil pressure related but this model shared the same circuit for level & pressure to trigger the lamp which can fool a few people, can you put a test gauge on where the pressure sender is!

cheers zeph - I'm not sure if this one has an oil level sensor, but I think I'll remove the sump anyhow to check the pick up strainer.