1998 Johnson Evinrude "EC" 2 thru 8 Service Manual, P/N 520202, Page 219Get this manual
25Pressure and vacuum test the gearcase as follows:
INote Pressure and vacuum test gearcase before filling Remove the oil level plug and screw in pressure test gauge Pump pressure up to 3-6 PSI (21 -42 kPa)If pressure gauge indicates leakage, submerge the gearcase in water to determine source of leakage as evidenced by bubblesIf the gearcase pressure gauge does not indicate leakage, increase pressure to 16-18 PSI (110-124 kPa)If pressure does not hold, submerge the gearcase in water and check for source of leakageMake necessary repairs and repeat test Install vacuum testerPump out to 3-5 inches (76-127 mm) Hg and see if vacuum holdsThen pump out to 15 inches (381 mm) Hg and checkIf the gearcase fails to hold on either test, put oil around suspected sealIf leak then stops or oil is drawn in, that seal is defectiveReplace defective components, test, and fill gearcase