I use Mobil1
synthetic. When I replaced the 20W-50 builder fill with 5W-30 Mobil1 my
oil pressure went up! I figure the thinner
oil went through all the plumbing of the cooler and hoses more easily than the Parrifin
oil did.
The thinner oil also means it pumps more easily and put less stress on the oil pump gears. At 2000 RPM I have 55 PSI with a crate 351W.
Bob