Mariner 175 HP OB -1993

by Patrick O’Hagan
(Mayo, MD)

Mariner 175 HP OB -1993

Having overheating problems. New impeller and new thermostats. I noticed that the thermal vacuum valve (Part #814612) is broken/ new one ordered. One of the two connections (the one closest to the engine) is still attached to the vacuum line that goes to the carbs.

1.) Does anything connect to the other nipple? Does it just let ambient air in?
2.) Will this parts failure cause overheating and rough idling?

The mechanics I normally go to with problems that I can’t fix are Johnson/ Evinrude guys and aren’t familiar with this part.