The Red Oil light thread E39 540i
 

I am creating this thread in hopes of consolidating the collective knowledge of the community on this problem. I understand that many have experienced this issue. I'm experiencing the red oil pressure warning light at idle only after the engine has warmed to operating temperature. I otherwise don't have any other symptoms although I will occasionally feel an odd vibration or stumble as well as an rpm dip when it occurs. Anybody with experience is encouraged to post their findings.
Thanks

Delo 400
 

My first 97 540i, had this same issue at around 150K miles. Took it to (2) different dealers at some cost and even had the oil pump pulled and checked. (2) new oil pressure switches and still the issue. Finally tweaked the idle to run a bit high and got it to go away for a while. Moved to a diffeent area and another dealer said I was running the wrong oil. I had used Mobil 1 since new (changed twice as often as recommended) and he highly recommended Delo 400 (diesel spec) and the problem was solved. Sold the car last year with 230K and I did not have any other issue with the light.

Ordinarily, this is a sign of worn crankshaft bearings. How many miles on your car? More than 200,000? I say "ordinarily" because the bearings on the 540 are pretty long-lived, from what I've read here. There may be other causes, like a bad oil pump, but beyond that I have no idea.

I think it's more accurate to say that the symptoms were ameliorated, but the root problem wasn't really addressed. Normally, these engines are capable of running a variety of viscosities without the low oil pressure light illuminating. The question is, what happened to change this?

Another thought, in light of the stumble or vibration: Have you noticed the rpm's when this happens? If it's dropping below 500 rpm, the problem might simply be the idle control.

Dunno if the OP looked in the bestlinks yet, but here's what I found (among others):
- E39 (1997 - 2003) > Low Oil Pressure warning--possible cause
Here's just one post of that thread ...

Although the explanation in this post sounds bogus, it relates a symptom potentially very similar to the OP's. If you substitute the "unmetered air being pulled across the sensor causes the computer to think there is excess air (and not enough oil) in the crankcase" and just substitute, "causing a drop in idle speed" (say, below 500 rpm), it seems perfectly reasonable that this poster's oil warning light could have been caused by something like a vacuum leak.

I am the third owner and the odometer reads 146,xxx miles. I have also heard that too-large clearances in bad main bearings could be the reason the oil pressure is low. I hope not.

This is a good question bobdmac, and the answer is no the idle does not go below 500. Using OBC test # 7 and reading the digital tachometer it never goes below about 520 at the lowest.
Another thing of interest that I failed to mention is that sometimes when braking to a stop the engine will stall out. The revs will just fall and the motor will just shut off, as if the key was turned off. I don't know if this is related in any way, but thankfully it does not happen often. I first thought this was an electrical issue but now I'm just not very sure about anything. Thanks again to everybody for making this forum great.

The only thing that I can think of as far as anything like this goes is that perhaps my leaky valve cover gaskets have something to do with it? However, it is to my understanding that the crankcase has a positive pressure on it so I don't see how a vacuum leak could affect this.

This sounds like it's related to your stumble and vibration at idle issue. Have you gotten any diagnostic codes? I think it would also be worthwhile to hook up an oil pressure gauge and get a reading at idle. I'm guessing oil pressure at idle should be around 15-20 psi, but I haven't bothered to look it up.

Check out this thread, on Bimmerforums. After getting a low pressure reading with a mechanical pressure gauge, the party replaced the oil pump ($400), apparently fixing the oil pressure problem. He had no associated idle/vibration issues and no complaints about cutting out on braking.

Any car with this problem probably suffered from the old drive it like you stole it break-in technique. :D

Here's another potentially helpful thread (Bimmerfest), particularly post #34:

Then i found a interesting site about OBD and accessing its menus. Test nr 7 lets you monitor your engine core temperature, wich on the 540 is supposed to be at 105C (thats when the thermosthat opens). Ok guess what mine was... 117C And when the engine got hotter the oil light flickering was more frequent. then i got it, Its a temperature related problem not a pressure related. Im using 5w-50 synthetic oil. I believe the oil gets too hot and too thin, thats why it loses pressure, and thats why i notice more oil loss due to bad valve cover gaskets for example. (did the valve covers later and no leaks now also did the valleypan and oil pan gaskets, oilpump was tight, no missing or loose bolts)
Someone previously posted that a shut thermostat overheats the car in 10 seconds - well not really, it still permits the water circulation in the small circle, the big on is shut. The temp. needle begins to move on the 540 at about 114C so mine overheated only 3Cand never reached the red zone, dont really believe that it destroyed my head gaskets or did anything harmful to the heads. The play is between 105C and 114C. For example if its constantly 111C theres a problem, but the car doesn´t show it. the funny thing is that usually thermostats get stuck open when they fail, but the v8 ones seem to close. And theres some electronical device in them. A new one was available only at the dealer and cost me 120-130$ But it did the trick for my car so money well spent. I still think that depending on the level and spec of oil and on the condition of the oil, temperatures about 110C can and will induce the flickering oillight.

This party solved the problem by replacing his thermostat. By the way, in digging through the threads, I found numerous references saying that the oil pressure at idle should .5 bar (about 7.5 lbs).

Bobdmac, thank you again for your help. Okay well I am going to read through the thread on bimmerforum that you linked me to. I have a new thermostat and water pump as I did a cooling overhaul on my car when I got it. I have actually looked at test #7 for KTMP to see at what temp does this happen. It usually happens after the dummy temp needle reaches the middle and the temp reads ~105 degrees. My motor does not overheat or lose coolant, etc. I know that I need to check pressure with a mechanic gauge. Any tips on renting/purchasing a guage set? After that my next move is to drop the oil pan and see if I can find any obvious clues.

Update: Today I added some more mobil 1 10W-40 and filled it to the max line(as I always have done), I dorove around for a while, certainly long enough for the problem to rear it's ugly head, but lo-and behold, it did not come on in. It flickered a couple time but did not keep staying on at idle anymore. I will go for a drive later tonight and see what happens.

That sounds interesting but inconclusive. I'm still curious to know what the actual oil pressure is.

I feel the same way, believe me! I want to get my grimey paws on a mechanical pressure gauge to see whats going on. I think I will try to do that asap. I can't believe that it didn't come on. I even drove spiritedly a bit just to test it. Never showed up. Go figure.

How much oil did you add?

I added about a half-quart bringing me right up under the max line.

I just began experiencing this same issue this morning. My most recent maintenance was an oil change but instead of using the normal Mobil 1 0w-40 I chose to try the Mobil 1 0w-30 instead. I wonder if this weight is too thin. I also know my VC gaskets are leaking but i have no puddles of oil under the car.

Should I swith back to 0w-40?

Did you search forum for loose bolts on the oil pump?

Negative. My understanding is the oil pump lasts forever. I don't even know where it's locate.

The Oil Pump lasts forever but the bolts for M62 Oil Pump are known to work themselves loose!!!

You need to google "bmw m62 oil pump bolts" and start reading LOL.

Ok gotcha! will do! LOL

One more question, if they work theymselves loose will i notice any puddles of oil under car?

Yes,

Oil Pump is inside the engine, you can't see it w/o removing the oil pan.
And Yes, when the bolts work loose, the oil pump simply does not put out adequate oil pressure (very much like a failing heart during a heart attack).