James, here in the backwaters of CA. (i.e., Fresno and the central valley) we
regularly have overnight temps of 29 to 35 degrees F. I run a 20/40 oil and
at start up the pressure runs 55-60 lbs and then drops to 55 lbs after the
car warms up. Even in our triple digit summer temps (110+ F) the oil pressure
remains constant at 50 to 55 lbs. I believe that your oil is pretending to be
much more viscous than it really is and the effect of the cold is amplified
by the large volume pan resulting in the oil taking longer to reach operating
temp.
I lived in New Orleans for three years (when I was still young enough to be
able to party and go to work the next day) and upon returning to CA. had to
change the oil in my pickup. The oil I had at the time was purchased in New
Orleans. After the change I noticed the range of oil pressure varied at a
different rate than when in New Orleans. I attributed this to regional
blending for optimal performance based on temperatures of the area where the
oil was purchased.
Finally, the plastic pressure line may be reacting to the cold and
restricting the pressure reading until it warms up.
It would seem that all of these explanations may hold some sway in the
discussion. Unless you have change the brand/type of oil and filter or other
components the one variable is the temp. Try putting the car in the garage
where the overnight temp remains higher and then check results in the
morning. Then try piping warm air under the dash after leaving the car
outside overnight and then starting. I believe that this highly scientific
approach will give you answers. Finally, don't worry you still have adequate
pressure at start up. If you are still uncomfortable, keep the revs down
until the temp comes up. (Remember, that leaving the car at idle to warm up
can cause excessive wear with extra fuel washing away the protective oil
barrier on the cylinder walls.)
Hemmings new mag. Rod and Custom has an excellent article on oil this month.
If you can't find it I'll scan it and send you a copy.
Keep the revs down when cold and enjoy the humidity!
Dr. Moonstone
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