had cowl off motor yesterday and notice an oil residue on the starboard side of motor. investigated and found a small hose going from bottom of motor to the top was dry rotted and cracked. the hose is very small on the inside, about 1/16. the fitting it connected to on the top was brass with a barbed hose fitting and a screen on the other side. what is the purpose of this hose, is it an oil transfer for lubrication?
Yes its for oil transfer. Don't know if you can just replace the hose and reuse connectors or not. Thought I would give you a bump as this seems like an easy question for the experienced posters to answer.
They are called bleed lines. One of the fittings at the end of the line is a one-way check valve. The fitting at the other end is just a pass through. The check valve fitting must work properly for the oil to move though the line. Do a search for "bleed" and you will find more detailed discussions on how to test the bleed line check valves.
1996 Mercury 150HP V6 carbed outboard motor and Maxum 1900XR bowrider boat
Mark, That hose directs oil from the bottom main bearing where it has settled in the crankcase due to gravity, to the top main bearing to provide lubrication. The bottom brass fitting is a one way valve. Replace the hose.