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Poppet Valve question, 94 Yamaha 115.

K

Klink

Regular Contributor
If memory serves me correct, I remember reading somewhere that the poppet valve opens only when the engine is at higher speeds (because of higher water pressures from the water pump) and it dumps the water out through the overboard exhaust pictured below. The if at high speed, water is not pouring out the overboard exhaust, your poppet valve is stuck closed.

Am I correct? I can't find a confirmation of it online.

Yamaha 115 overboard exhaust .JPG
 
Your memory is off. Happens with us old dogs.

You are correct about the operation of the pressure control valve/pressure relief valve/poppet valve. It opens to keep water pressure from getting too high.

Water does not always flow out of the idle exhaust port. It normally flows out through the lower unit and then out the propeller hub.
 
Not your specific 115 but the one depicted below gives a generalized idea of water flow. This one uses two PRV's whereas yours uses but one.

 
Thanks for the explanation and schematic. I was using a hose to flush the engine, so there would be no water back pressure on the through the propeller exhaust, hence no water is coming out of the idle release hole of the upper case. If I test it in a tank instead or on the water, then I'll see water at idle out the idle release hole of the upper case. At high boat speed on the water, I should see even more water coming out of the idle release holes because the pump will be cranking at maximum pressure.

Correct?
 
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boscoe said:
I don't think so.
Click to expand...

Heads were disassembled and manually cleaned, new gaskets, thermostats. I tested the engine in a tank, and the water pressure at idle was 10lbs and the water temperature was at 140. At 1800 neutral rpms the water pressure was 20lbs and the the only water that came out of the overboard exhaust holes was some spitting. So you were right.

I am getting a little sweating of water through the head gaskets sides (nothing appreciable). Everything was torqued to spec. I'm thinking that when the engine heats up with a good run on the ocean, that the seals will heat up and seal completely. BUT, I am worried about the poppet valve being stuck, it seemed to be a tad tight in the hole, it is the old style poppet that goes into the hole. How does one know that the poppet is not stuck closed? Water pressure goes above say 30lbs?
 
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