1971 Johnson 60HP outboards Service Manual, Page 58Get this manual
THERMOSTAT RECIRCULAT ING WATER
DESCRIPTION
EXHAUST HOUSINGS The 60 HP model features "wet sleeve" exhaust system consisting of an inner and an outer housing with water chamber in betweenThe water discharged from the engine cooling system fills the space between the exhaust housings and maintains specified level when the engine is runningSee Figure 6-1The water drains out when the engine is stopped and tilted above the water lineThis chamber of water serves as an effective silencer, quiets the exhaust relief, and cools the outer housing and lower rubber mountsExhaust gases are discharged underwater through the propeller hub for efficient silencing and performance