1977 70Hp Johnson - Valve, pressure relief

[Tortoise]

G’day
Wonder if someone can tell me the purpose of these 2x “valve, pressure relief” (#101 in diagram) in my 1977 70hp Johnno.
If I was to hazard a guess, perhaps they’re to relieve excess water jacket pressure if the thermostat will not open????

 

[racerone]

They open to allow extra water to circulate at full throttle,-----Thermostat controls water temperature at idle.-----Why the question?

 

[Tortoise]

Thanks. That makes sense.
I just like to know what’s what under the hood, and these look very stuck in place. Add them to the list.
Thanks again

 

[racerone]

Remove / replace rubber grommets.----Clean any corrosion found in there.----Replace water pump impeller if you do not know how old it is.