2003 Johnson ST 6/8 HP 4 Stroke Outboards Service Manual, PN 5005471, Page 50Get this manual
MAINTENANCE LUBRICATION
Oil Pressure Tests
Remove wire from the oil pressure sender and remove sender from the powerhead
Start enginePressure must be established within 10 seconds of start up at 900 RPMMinimum oil pressure should be: HP -15 psi at 900 RPM HP10 psi at 900 RPM Maximum oil pressure should be: HP35 to 40 psi at 4200 to 5200 RPM HP35 to 40 psi at 4200 to 5200 RPM If test results vary, check the following: Oil level Clogged oil filter Clogged internal passages Clogged oil inlet screen or tube Stuck or defective pressure regulator Defective oil pump