Its back....low oil red light...STOP Engine oil pressure

[GiantClam]

It happens on hot days. After 3 hours around town...first the oil can, then STOP SHUT ME OFF AHOLE...then low oil...it all vanishes when the weight of my foot raises it 100rpms.
The car was in car ICU..hooked up to every machine known to man...Nothing...pressure test, got into the data..changed the pressure sensor.....external temp sensor was telling me it was 105 degrees out...but its about 85..changed that..I believe my aux fan is dead, was on for 15 seconds, cold start, AC on....im going mad.
2003 530i
Thank you in advance, Clam

[edjack]

What is the actual oil pressure, as measured on a mechanical gauge?

Possible failure of the pressure switch on the oil filter housing. Change it, but be sure you change the correct one; the oil temp gauge looks the same.

Note that the ambient temp sensor measures the pavement temp, because of where it's positioned.

[pleiades]

It happens on hot days. After 3 hours around town...first the oil can, then STOP SHUT ME OFF AHOLE...then low oil...it all vanishes when the weight of my foot raises it 100rpms.
The car was in car ICU..hooked up to every machine known to man...Nothing...pressure test, got into the data..changed the pressure sensor.....external temp sensor was telling me it was 105 degrees out...but its about 85..changed that..I believe my aux fan is dead, was on for 15 seconds, cold start, AC on....im going mad.
2003 530i
Thank you in advance, Clam

Seeing more threads of this nature over time ....

In my case, it was a faulty light control module (LCM) with a roasted chip inside. The LCM sends that message to the cluster. Not saying this is your problem, just another item on the checklist ....

How many miles on your car?

[bdiefAZ]

Low oil warning can be from a faulty oil level sending unit located at the bottom of the oil pan.

Part number: 12617508003

[GiantClam]

150.....original owner....03 530.
Im thinking a cooling issue too...plenty of airflow on the highway.....around town..not so much...takes a few hoursnto happen...

[E39 Newbie]

Had the same problem on my E46, M52TUB25. Turned out to be a weak oil pump. I crutched it for a while with Liqui-Moly's oil additive which upped the oil viscosity a bit. I replaced the pump and it's been fine ever since. In retrospect it was probably a weak spring in the oil pump, but as long as I was in that deep, what's a few extra dollars for a complete pump?

[Chedley]

+1
It’s most likely an oil pump buckling.

It isn’t a cooling issue. If anything, heat increases the oil pressure, doesn’t lower it.

[R Shaffner]

+1
It’s most likely an oil pump buckling.

It isn’t a cooling issue. If anything, heat increases the oil pressure, doesn’t lower it.

Respectfully disagree. All oil gets thinner, less viscous, with heat. Thinner oil flows easier, which reduces the pressure.

[Chedley]

Yes oil flows easier with heat.
But all parameters being equal, an increase in temp will increase the pressure of any fluid:
P.V=R.T (Pressure, Volume, Temperature, R is constant for a given fluid)

[R Shaffner]

Yes oil flows easier with heat.
But all parameters being equal, an increase in temp will increase the pressure of any fluid:
P.V=R.T (Pressure, Volume, Temperature, R is constant for a given fluid)

I have no desire to argue, but that science doesn't apply to this situation. That equation has to do with applying heat to something in a confined space. Here the space is not confined. The oil can expand in the crankcase without constraint, and just push a little air out. (The pressure being discussed here isn't in the crankcase. It's the pressure from the oil pump as it pushes the oil through the oil passages to important parts of the engine.)

What does apply is the fact that hotter, thinner oil flows more easily, so it provides less resistance. That means the oil pressure at idle on a hot engine will usually be less than it is when cold. That's true even with multi-viscosity oils. And if the pressure is low enough, it can make the oil light come on when the sensor is based on oil pressure.

[JimLev]

I have to agree with StephenVA as I have had an oil pressure gauge connected to the filter housing in the past.
Cold idle at 550 RPM was around 40PSI, maybe 45. At hot idle (same RPM) it was 8-9 psi.
The oil pressure switch will trigger at 7 or lower PSI.
Turn the AC on to increase the idle and the pressure will increase.

[GiantClam]

Update....Last 2 days in NY were hot.
Removed front bumper to put in new aux fan ( which of course wont work)
That said....with the front bumper off, for 2 days and about 150 miles..stop and go, highway....the oil lights vanished...all of them.