I run 10W30 in my '51 235 which is the same engine just diffrent displacement. it calls for 20 or 30w by the manual and use non detergent 30 weight if you don't have an oil filter. they idle around 5-8 PSI oil press and usually read just over 1/2 gauge at cruise. which is just about 15 PSI... crank it over without ignition, to get the oil pump going then fire it up