Re: Oil pressure

[jlandry@domain.elided (John A. Landry)]

LATE BREAKING NEWS: Russel DeArman <russde_93@domain.elided> wins the 40
million dollar lottery and says:

>  I put in 10W-30. My oil pressure is now doing funny
>things. When cold the pressure will take a while (10
>sec. or so) to come up to around 45 on the
>after-market mechanical gauge (dash one doesn't work).

This isn't abnormal, although 10 seconds seems a little long.  Both my old
200,000+ mile 345 and my new 392 do this.  It simply takes some time for
the oil pump to push the oil up into the engine passageways and pressurize
the system.  The pressure relief valve should limit the pressure to
something like 55 psi, so if 45 psi is the limit you see (and you can trust
the accuracy of the gauge), then this is a sign your internal engine
clearances are getting loose through normal wear and tear.

>Once it's warm, at idle the pressure drops to <10, and
>at highway speeds (2600 rpm's) it will only reach
>30-35.

Again, this isn't abnormal for a high milage engine.  With 10-30 my new 392
(with tight clearances) has a hot idle pressure of 10 psi and a highway
cruise pressure of about 35 psi.

An old rule of thumb (I'm not sure how valid it is) says that 10 psi per
1000 rpm is acceptable oil pressure.  You have that and more.  As long as
you don't have lifter clatter (except *maybe* briefly at startup) then you
have nothing to worry about.

>  I am thinking I should replace the 10-30 with 10-40,
>but I am also concerned with the length of time it
>takes to build pressure when cold. Should I
>rebuild/buy a new oil pump? Can this be done
>'in-truck'? i.e. without pulling the motor?

Very likely rebuilding the starter (new ones aren't available) will not
increase your pressure substantially.  A complete engine rebuild would be
needed to close up the internal clearances.  But again, you don't really
have a problem worth worrying about.  You might want to switch to a
slightly heavier oil in summer like 10W-40 or 15W-40.  10W-30 is still
probably good for the winter months.  You might loose a little fuel economy
with a heavy oil, but not much with an IH.

Take care,

John L.
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