Mysterious hole

[maksio]

On the Tohatsu two-stroke engine column, there is a hole at the top of the back.
Various things fly from it: exhaust gases and water.
I have several different engines of this type: 9.9 15 18 25 and 30 HP - and they fly differently!
Who will be polite and explain to me what role this mysterious hole plays (because the exhaust is through the screw) and what and when should it fly from there?
Water: warm? cold? much? a little? exhaust?
Thank you very much for understanding my inquisitiveness

 

[GA_Boater]

The hole is called an idle relief. The purpose is for release of cooling water and exhaust gas pressure when the through prop exhaust is water filled at idle when the exhaust cannot overcome the weight of the water. Once a boat begins to move as RPMs go up and the prop spins, exhaust can exit through the prop.

 

[maksio]

Cool!
thank you very much!
So little reading - and I learned so much
So: by controlling the work of the water pumping system you should add the amount of water from the control hole and this "mysterious hole" Great!
Does it have anything to do with the thermostat?

 

[GA_Boater]

Nothing at all.

 

[Sea Rider]

Don't know about the 8 and 9.8 HP motors, but on the larger HP ones those holes are called Cooling Water Check Ports and work all the time whether the motor is being flushed on a barrel, muffs or running on open water. Place your extended palm there and will feel how the water varies its temp as the thermo opens and closes, good indicator that the thermo is doing its homework right. Should feel medium hot to warm temp depenfing if the motor was running at slow or high rpm, but never should burn you hand.

Happy Boating

 

[maksio]

Sea Rider
I meant the hole in the back - not the water control. There are various things happening there - now I know that it is an "exhaust of idle" and I know why! I was wondering if something changes there depending on the condition of the thermostat.
But GA_Boater said no.
I was wondering why different amounts of water flow - in different engines and with different strength - but because it is the exhaust, even the condition of the engine has an impact on it! The condition of the water pump - too!
Ok - I'm smarter thanks to you.
Thank you again!

 

[Sea Rider]

Sea Rider
I meant the hole in the back - not the water control. There are various things happening there, was wondering if something changes there depending on the condition of the thermostat.

Assume you're talking about 2 strokes motors, right? If so, the large hole at middle upper lower leg is what told you it was called, the other one with a tiny hole at side it's the water indicator also known as the peeing port, which only tells if the water pump is working ok, but if it's clogged with salt, debris, whatever won't see a drop being peed.

The amount of water exiting "the hole" will depend entirely if the motor was running at idle, medium or max wot rpm range, the more rpm the more amount of water will exit, it's temp will also vary if having an immaculate free internal water cooling passages or a very salted one along and most important an impeller working spot-on.

Happy Boating