Re: [DML] Low Oil Pressure @ 10W30

[Scott McMullan <smcmullan@xxxxxxxxx>]

I described this issue over the summer in detail on this list, using a
different email address.

I had my oil pressure gague's accuracy tested, and it was fine.

As long as I have 20w50 in there, everything works according to spec;
pressure reads in the normal range and behaves as expected (needle
just about horizontal at idle, and near the top of the range when
running pretty much anything over 1K RPM.

If I put lighter weight oil in, about 10 minutes after the engine is
at normal operating temperature, oil pressure at idle reads less than
half the normal idle pressure, and the longer I run the lower it goes,
almost reading zero after 45min or so of driving.  With the engine
over 1K RPM, the pressure is on the gague, but lower than normal.  The
oil pressure light NEVER comes on when the engine is operating.  I had
10W30 in there, then moved to 10W40, with no noticable improvement. 
Change oil back to 20w50, and the oil pressure starts behaving
normally (although it was funky for the first 150 miles, like it was
working its way back to being OK).

While the engine was generally louder than normal with the lighter
weight oil, I don't recall any specific clattering that sounded
"wrong".

Maybe my engine had bad internal wear, I really don't know.  But I
*never* have any problems starting in the cold.  It was near freezing
on Thursday morning, and the engine fired right up on the 1st try, as
always.

I have never found anyone who could give me a good reason for this
behavior, I was just guessing at the oil pump.  One shop I consulted
when I first started having this problem (a friend of mine works
there) tried to tell me that the engine was probably shot, and putting
heavier oil in wouldn't help the symptom.  I found that hard to
believe with about 60K KM on the odometer... glad they were wrong.





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