Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

boatmon345

Petty Officer 2nd Class
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Apr 26, 2006
Messages
113
Hello,
I discovered the nipple housing of the exhaust manifold water pressure valve has cracked and is in the middle of disintegrating after discovering water was coming out from below the cowling, and the spring is exposed. I have had no problems overheating to my knowledge.

I figure I will replace the nipple housing, spring, valve, and grommet.

However, I don't think this valve assembly serves any purpose on my engine. The reason is because the plasitc valve inside does not slide, and if I remember correctly when I personally rebuilt this engine in 2006, the valve didn't slide then either.

Several questions:
What is the purpose of this valve, and under what conditions is it closed or open?

I am thinking about capping it off on both the exhaust mainifold side as well as the hose side because saltwater seems to shoot up into the nipple housing, doesn't pass, and slowly eats away at the housing causing it to corrode.

Thoughts please, thank you.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

When at low RPM the PRV is closed with spring pressure, if it sticks open the motor will not fill up with water and you end up with no cooling at the areas with no water to them.
High RPMs will cause water pump to build up pressure and will open PRV to release some of the water.

Keep the motor the way it was designed
 

Ldavidgrover

Petty Officer 2nd Class
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Feb 22, 2012
Messages
197
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

There was an update on the valve. When you get your new one it should be mushroom headed instead of the straight 4 blade that always stuck in place. I'm surprised that you exhaust plate isn't corroded out too.
 

boatmon345

Petty Officer 2nd Class
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Apr 26, 2006
Messages
113
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

Thank you both for your replies.


PressureValveHousing.jpg



Corrosion.jpg


The exhaust plate side wasn't too bad after I cleaned all the corrosion out.
 

robert graham

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Apr 16, 2009
Messages
6,908
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

Best to clean it out best you can and replace all parts,valve, new gasket, etc., then inspect yearly for new corrosion and valve operation. Considering the amount of corrosion deposits there, maybe your motor would be a good candidate for a yearly "Saltaway" flush? Good Luck!:)
 

boatmon345

Petty Officer 2nd Class
Joined
Apr 26, 2006
Messages
113
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

I think what's been happening is that the valve has been stuck shut since 1996, and the hot salty water has been backsplashing up through that tube and slowly eating away at the valve housing which never had received the pleasure of a freshwater flush.

Is there really that much pressure that can come from the impeller to counteract that tough little spring enough to open the valve?
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Purpose Of Exhaust Manifold Water Pressure Valve - 97 Yamaha S150TXRV

I can't explain the exact workings of my outboard's cooling system, but I sure wouldn't think to eliminate any integral part of it. If that valve wasn't important I expect Yamaha would just save their time and money of putting it on the motor. But I'm a long way from being an expert on these motors, and hopefully one of the guru's on here can better answer your question. Good Luck!;)
 
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