1997+ Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-826148R2, Page 190Get this manual
Check Valve NOTE: heck valve can be replaced by removing intake manifold when powerhe ad is attached to driveshaft housingThe check valve is 316 in(4.76 mm) diameter brass casing containing nylon ball-valveIt can be damaged by hot combustion blow-by into crankcase (ie backfire, or hole in top of piston, etcTO CHECK: Inspect check valve by looking through holeIf light can be se en the nylon ball is bad (probably melted); PLA valveIf you se no light, insert fine wire into check valve hole to se if there is slight movement of nylon ballIf ball moves, valve is .KR eplace valve if ball does not moveInstall check valve into check valve holder as shownAir
Thermostat
Wash thermostat with cle an waterUsing thermostat tester, similar to the one shown, test thermostat as follows: pen thermostat valve, then insert thre ad betwe en valve and thermostat bodyAllow valve to close against thre ad Suspend thermostat (from thre ad) and thermometer inside tester so that neither touches the containerBottom of thermometer must be even with bottom of thermostat to obtain correct thermostat opening Fill thermostat tester with water to cover thermostat Plug tester into electrical outlet bserve temperature at which thermostat begins to openThermostat will drop off thre ad when it starts to openThermostat must begin to open when temperature re aches (3 C) above designated stamping on bottom of thermostat