One water tube has two small drilled holes in it between the water pump and the adapter plate. Do they just relieve pressure when the thermostat is closed or some other purpose?
I'm told they cool the exhaust. I guess it keeps the exhaust tube cover from getting too hot. Nothing spoils a day on the water like burning yourself on the motor.
My old 60hp has them too, I figured they were some sort of air bleeds eliminate air pockets but it's just a guess, the exhaust is mixed with cooling water internally as it it exits a water mist right?
They cool the exhaust and more importantly, they protect the rubber hub inside the prop from melting and spinning loose on thru-hub exhaust propellers.
All outboards have some type of water spray to help cool and quiet the exhaust areas.
