Diesel water valve

[RAD88]

This is a pic of the water valve on my Yanmar YSB12. It has been in this position (open - I think) for 6 years and no water has ever come out of it. I have tried to turn the handle but it will not move and I am afraid of breaking it off. Now it has started to leak a little. What is this used for and how can I fix it?

 

[Chris Patterson]

I can't see where it goes, but it was definitely meant to drain. And it is in the open position, so it may have plugged long ago. Common looking little dump valve, with what looks like 1/4" NPT threads.
When you unscrew it, who knows what junk may emerge..

 

[Apex]

I have a different petcock in the exactly same location on my YSM. It drains the head of cooling water. I pulled mine (1st season winterizing) as it was also stuck open due to crud not allowing it to close. My plan is to clean out the water passages on the head come spring.

 

[Jalepeno]

That is the cylinder raw water cooling chamber drain petcock. My 1979 YSM-12 has a slightly different one. Carefully unscrew it (metric thread) and clean it out the passage with a wire. You will probably also need to use a small screw driver to break the deposits from the cylinder chamber hole to allow the water to drain out. Not sure if there is a need to or what is the best way to clean the cooling chamber. “Salt Away” or “CLR” or ?

 

[Apex]

recirculate muriatic acid

 

[Benny17441]

Would suspect the petcock was turned into the open position but the valve is closed. The valve stem just twisted under force. Replacing the valve is the only way of fixing if my hunch is right.