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<02> Oil Pressure

Dan Chapman <R2002tii@domain.elided> said:

> I ... put an oil pressure gauge on my "new" motor.  When the car 
> is cold, I have a ton of oil pressure (the slightest touch on the 
> gas sends the gauge flying), about 20-30 psi at idle, but when 
> the car warms up, I get no more than 20 psi at idle (sometimes 
> the idiot light comes on), and the maximum is about 30 psi (even 
> at 7000 rpm!).  Is this normal?  Brand new oil pump, Mann oil 
> filter, using 20w-50 oil ... ['73 2002tii]. 

The BMW Repair Manual says the oil pressure idiot light switch should 
close when the pressure drops below:  

              0.2 - 0.5 bar  (2.8 - 7.1 psi).

The oil pump pressure specs are:

      Idle:   0.8 - 1.2 bar  (11.4 - 17.1 psi)
              0.5 - 1.5 bar  ( 7.1 - 21.4 psi) "Gear type oil pump"
  4000 RPM:  approx 4.0 bar  (     57 psi    )

Something is not normal.  You should consider the possibility that
your gauge is inaccurate.  Your oil pressure switch could also be 
faulty, although it's common for the light to flicker at _low_ idle 
when the engine is hot.  Can you try a different pressure gauge?
If your present gauge is accurate, then you do have a problem.

Curt Ingraham
ingraham@domain.elided