What is this valve on my yanmar?

[Aklein620]

What is this small valve and drain for?

[vw1961]

it looks likw the drain for the primary circuit engine coolant

[Aklein620]

In what circumstance would you use it?

[Emmalina]

When changing coolant !

[OloteleMtn]

When prepping the boat for winter storage, to keep the coolant from freezing, expanding, and cracking the engine, or to drain the head and block prior to removal of the head for service or repair.

[Uncle Bob]

Originally Posted by Aklein620

What is this small valve and drain for?

It looks to me like the valve is in the raw water fitting at the end of the heat exchanger,I would guess to facilitate raw water system drainage for winterization.

[Wotname]

I'm with Uncle Bob! Looks like the raw water drain of the the heat exchanger or exhaust manifold.

However if you tell exactly what model your Yanmar engine is, then we can tell you exactly what it does.

Or you can read the engine operation manual!

FWIW, see also https://www.cruisersforum.com/forums...38#post3162838

[bensolomon]

For draining fresh water from the engine during winterization.

[DougR]

Uncle Bob has it......
It’s the sea water drain for the heat exchanger tube bundle.

The freshwater coolant drain appears to be just below the throttle cable clamp bracket.

[Wotname]

You've got sharp eyes DougR