A quick glance to the BL Service manual:
Recomended oil weights at temperatures:
Above 10 degrees farenheight (-10 C): 10W-40, 10W-50 or 20W-50
Between 0 and 20 degrees F (-15 to -5 C) 10W-30, 10W-40 or 10W-50
Below 0 degrees F (-15 C) 5W-20 or 5W-30
Oil pressure range:
948 and 1098 engines: idle, hot:10 to 25 lb/sq.in, normal running 30 to 60
lb/sq. in
1275 engines: idle, hot 20 lb/sq.in, normal running 40 to 70 lb/sq.in
With the modern oils, 20W-50 is my choice, because I have other cars to
drive when the temperature drops below 50 degrees. While I have had the car
in snow country, even there I never took the car for a drive with the
temperature was below 10 degrees. I have experimented with Syntec 5W-50, as
the higher the second number, the thicker the oil at opperating temperature,
and the thicker the oil, the higher the oil pressure. Although I have heard
that too high of oil pressure can cause as much damage to engine bearings as
too low of oil pressure.
30 lbs. in a 1275 when hot at normal speed (3000 RPM and above) is a little
on the low side, but 20W-50 would probably raise that to an acceptable
range. The addition of an oil cooler is also usually good for a few PSI.
If you aren't racing, the engine isn't knocking, and idle oil pressure
continues to stay above 10 PSI, I wouldn't worry unless you notice a gradual
decrease over time.
YMMV, just MHO, yada, yada, yada...
David Riker
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