On Mon, 10 Jun 1996, Will Zehring wrote:
> Fellow fiends:
>
> I am catching up on the digests (I've been out of town) and read the posting
> regarding fluctuating oil preasure and have grown confused.
Wow... What dedication... I just unsubscribed while I was gone; this is
my first post on returning.
>
> --How can the gauge be reading 90lbs if the engine has a 60 lb oil preasure
> relief valve? Doesn't the valve open at 60 lbs and therefore establish an
> maximum upper oil preasure at about 60 lbs?
The relief valve is only in its element when the oil is hot; from cold,
it is not at all difficult for the high pressure and viscosity of the oil
to "overwhelm" the relief valve.
It is also possible that the valve can be stuck shut, either from grit
etc. in its bore, or from a blocked drain passage behind the piston
resulting in a hydraulic lock type condition.
When the two conditions coincide (thick oil/stuck relief valve), look
out. We have a BMW with a stuck relief valve, and every time the engine
is started at below 10degF, it blows the oil filter apart. Quite
entertaining, if you're not the one that has to clean up the mess.
> --why was the engine designed and built with a 60 lb oil preasure relief
> valve if it can run happily and safely at 90 lbs?
Because 60 psi is enough. Raising pressure to 90 psi will not improve
lubrication or protection any, but it will use (a teeny tiny bit) more
power and then there is the danger of developing leaks, occasionally of
the spectacular variety.
> Or, am I completely missing the point (again)?
It's OK, Will, as you doubtless know by now, missing the point is not
only tolerated but encouraged on the list! I think MGs may in fact win
the coveted "Most-bizarre-segues" award for 1996 :)
Michael Chaffee
mchaffee@staff.uiuc.edu
[note new improved address]
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