RE: Oil pressure

["Dombey, John R" <John.Dombey@domain.elided>]

Bruce wrote:

> I've just had an oil pressure gauge added to the wife's Stag ('73 Mk
II)
> and am mildly concerned about the oil pressure. At about 3000 RPM
> after warm-up, it's 28-30psi. However, at idle (and I don't remember
> the idle speed; maybe 600-700 RPM) it drops to 8-12psi. Does
> anyone have any comparison numbers for me? I have my suspicions
> <sigh> and they aren't good.

Having been through the bottom end of my engine in the recent past and
verifying factory-spec clearances on everything, I can submit that the
oil pressure on a fresh engine seems to stay between about 40 and 60 psi
under all conditions.  I assume that the pressure relief valve is
setting the upper limit, and that things are tight enough to supply the
lower.  I've seen it drop very slightly below 40 psi on a hot day with a
slow (~700 rpm) idle.  I'd say that you've got a worn engine, but don't
get overly bent about it yet - keep an eye on the gauge and see if there
is any change over time.  Chances are you can safely drive for many
miles with these kinds of pressures without doing damage (as long as you
aren't autocrossing or being otherwise abusive).  I drove my TR6 with
low pressure for about 4 years, and on tear-down found that the oil pump
rotor had a crack in it, but that there was not abnormal wear on any of
the rotating bits (except the rocker shaft, which wears out when even
pressure is high...)

Just my thoughts and experiences - I'll be interested to hear what the
list has to say...

John
'69 TR6, '73 Stag, '81 TR8, '86 XJ6