Diverted water?

[A-Willing]

Can anyone help me figure out what these are? Look like a home made (abs) tank, with a 1/4” tube running from the freshwater hose between engine and transom up to the bottom of the tank and then a 1/4” tube running from the side of the tank to the port side exhaust riser Water jacket. There is one on each of my 1989 merc 4.3lx’s.

 

[Baylinerchuck]

I definitely don’t have anything on my 1990 4.3LX. Wonder if it was added to check proper winterization of manifold/ riser. Kind of like a sight window where antifreeze could be added?

anyway to contact the previous owner and inquire?

 

[A-Willing]

The previous owner was clueless. You may be on to something. The tank is under pressure when running and drains away when the engine shuts off.