E39 flickering oil pressure light

[bramley]

E39 530i, 107k

Oil level is to the max on the dipstick, but recently the red oil pressure light has been flickering on and off. It really is a flicker, it's not illuminated for more than half a second at a time i reckon. Seems to be fairly random - can't say it only happens at idle/when cornering/when accelerating for instance. Has only ever been serviced by main dealers and I've topped oil up with correct Longlife Castrol oil.

Hoping it's just a dodgy oil pressure sensor/switch but would welcome any ideas.

Now, I still have the engine light on which was diagnosed as a faulty oxygen sensor. Wondering if the two could be related? I read the o2 sensor issue could be caused by a vacuum pipe split, and someone on a forum suggested the oil pressure light could also be triggered by that - however, it was just one comment on a forum so not sure how valid it was as a suggestion.

I think the idle speed is a little lower than usual, and mpg may be slightly lower than usual but not 100% sure.

Re the oil, when I topped it up I was a bit worried to see a thin coating of rusty brown sludge under the filler cap - it doesn't look too serious, and one forum suggested They All Do That Sir??

Any help will be appreciated!

[HRG]

The vacuum pipe wouldn't cause the oil pressure light to come on IMO but it would definitely bring the engine check light on. Easy enough to replace but it might take a day or so for the light to go off as it's the long term map that brings it on IIRC.

Just had to replace that in mine. It's worth it as the extra cost in fuel will soon eat up the cost of the part.

[rm163603]

Rusty brown sludge... they all do that sir...

If the light is flickering randomly then it's almost certainly a dodgy sensor as you would expect a worn engine to show the issue at idle and not so much as revs increase.

Also to illuminate the light means there is almost zero pressure and your engine would be showing other signs of problems if that was the case such as knocking etc.

The only thing it could be other than the sensor I suppose is the oil pressure relief valve. If some crud got stuck in it it could be stuck partially open.

[bramley]

Thanks for the replies

[bramley]

Update - it is only flickering at idle. Does that help narrow down the possible issues?

[HRG]

It's either the sensor... Or low oil pressure

I'd either replace the sensor or get it checked out at a local indie. Oil is always cheaper than bearings

[bramley]

Fingers crossed it's just the sensor but am worried it's something more sinister. Will get it into the garage asap next week, would like to be able to go in there with some knowledge of the potential cause/solution.

[rm163603]

Flickering only at idle is more of a worry.

Causes could be:

Faulty sensor
Worn crankshaft bearings
Worn oil pump
Stuck oil pressure relief valve

I would get it looked at asap

[bramley]

Thanks for the reply.

The car is using a litre of oil every 1,200 miles or so, but that may not be connected as apparently some of them do that normally.

[rm163603]

I think a litre every 1200 miles is at about the limit of what's acceptable TBH. If you asked the dealer they would probably tell you it's OK though.

[BOR]

These oil pressure sensors are prone to this type of failure. Cheap to replace, even if simply to eliminate the sensor as the cause. For some reason, often exhibit these symptoms after oil has been topped up/overfilled.

IIRC, the sensor has a taper-thread, so don't over-tighten it.

[Shropshiremike]

bramley said:

Thanks for the reply.

The car is using a litre of oil every 1,200 miles or so, but that may not be connected as apparently some of them do that normally.

I can only think it would be connected if that oil usage led to it being run very low on oil. FWIW Dave, my cousin's 330i did about that sort of oil consumption when he had it, our 330i was hardly any with the same soprt of driving. People say it's down to how they've been run in, I don't know as we didn't have ours from new, but I think they modded the oil control rings at some point in production to try and limit the thirst.......certainly did on the M5 engine.
Hope it's just the sensor anyway

[miniman]

rm163603 said:

I think a litre every 1200 miles is at about the limit of what's acceptable TBH. If you asked the dealer they would probably tell you it's OK though.

blimey, mine has done about 12k since I bought it and it hasn't used any at all. Which reminds me, I really ought to change it as it currently wants an inspection service, an oil service and a brake fluid service

[bramley]

Dragging this thread back to life to add the cure for this in case someone does a search for something similar in future.

I had other problems with my 530 which are mentioned here: http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Anyway, it seems a lot of people here had correctly identified the problem. BMW replaced the crankcase breather valve and it's not only cured the lambda readings and the misfires, but also the flickering oil pressure light and apparently the car will stop using so much oil too, which is nice.

(Thanks to those people that contributed to the thread btw. If I had more time I'd have attempted the work myself.