My Bmw has 150,000 miles on it and has been religiously maintained. I'm
now getting the "low oil pressure" readout along with the warning bell.
This happens when the car is warmed-up and then parked for a few minutes.
Then it occurs at every stoplight. Once cooled down, it does not recur
until it is stopped and then restarted. Is this mechanical or just a tired
Yes, no panic, but at the same time this is not something to be delayed
looking into. You could do some serious engine damage if there really
is low oil pressure (such as was mentioned with the oil pump bolts).
As I said earlier, I would have the oil pump bolts checked:
This problem could cause both low, and intermittently low readings.
Definitely don't drive it until you get the problem (whatever it is) fixed.
We can assume by "local" you mean local mechanic?
More important is what is the oil pressure at idle (600-800 RPM)? The
oil pressure light sensor (a switch) turns the light on at 7PSI. If the
pressure is less than that with the engine warm - you have a problem.
As far as sporadic - it sounds to me as if you described a pattern, not
a sporadic happening. It is OK when the engine is cold (oil is thicker
and clearances are tighter = more oil pressure), it shows up after
running the engine, warming up the oil, stopping the engine (which
transfers more engine heat into the oil - thinning it) and then
restarting the engine. It then shows up when you come to a stop light
(where we can assume the engine is idling.)
The oil pump is engine driven. It puts out more pressure as the engine
speed increases. Oil - especially if you're not using a good quality
multi viscosity - or if the oil has been in the engine too long - tends
to thin out as it gets hotter - thin oil passing through the same
passages as thicker oil = less pressure. Engine bearing clearances get
wider due to the expansion of the metal as the engine warms up. The
engine is probably warmest when you shut it down hot and then restart it
while it's still hot. Wider bearing clearances allow oil to pass though
the bearings with less back pressure - lowering the oil pressure. ALL of
these can be combined to lower the oil pressure.
Given these symptoms, I have two conclusions:
1. Your oil pressure sender is bad - and triggering the light. It is
turning on at more than 7PSI of oil pressure at idle.
2. Something else is worn/wrong in the engine causing the problem. The
oil may be the wrong grade/viscosity, or may be old. The oil filter may
not be a stock BMW one - and it's causing problems. The oil pump may be
having the mounting bolts backing out problem - causing an internal
engine leak that lowers the oil pressure. The engine may be just plain
worn out due to lack of maintenance. OR all of the above.
I'd try to eliminate #1 first. The part is less than $20USD. It is easy
If this doesn't solve it - try an oil change with fresh oil of the grade
specified for the engine and a new BMW filter.
If that doesn't solve it - your mechanic is going to need to do some
investigation on the possibilities from #2.
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