Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 212Get this manual
Bleeding Air from Power Trim System To determine if the Power Trim system contains air, position engine so two trim rods are slightly extended Do not extend tilt ram Push down on lower unitIf trim rods retract into trim cylinders more than 18 in(3.2mm), it will be necessary to bleed airfrom the Power Trim systemBleed air from Power Trim system as follows: IMPORTANT: This trim system is pressurizedRemove fill screw (a) only when engine is trimmed to the full "up" positionRetighten fill screw securely before trimming engine downTrim engine or times thru entire trim range; check fluid level (fill if necessary) each time engine is trimmed to the full "up" positionSee "Checking Fluid Level and Filling," preceding