Re: 1975 135 horse evinrude
There are two identical 1/2" slotted screws on the starboard side of the gearcase, one above the other. The lower one is a drain and the top is a vent. You can remove the lower one first to take a sample.
When you refill,or drain, both screws should be removed, and the unit should be allowed to drain for at least 15 minutes, longer when cold. Turning the propeller occasionally will help.
Refill from the bottom until the oil flows from the top, then return the vent (top) plug first.
You need a high viscosity marine gearcase lube. The gearcase holds 27.9 ounces.
OMC recommended that the oil be changed once a year or every 100 hours of operation whichever came first.
