mercruiser water pressure relief valve question
 

p/n 863208a3 pressure relief valve assembly

I had another post about a water leak in the bilge, well, between a cracked sea water pump housing and this relief valve, the leak has been narrowed down. What was found with this valve, is the relief output does not have any water outputted when the motor is running at idle, or revved up standing still. But as soon as the boat is on plane, it will trickle water out of it. My question is, is the valve working properly, or should there be no water coming out of it until a certain psi (25psi), then have water coming out of it. Motor is getting proper cooling, that does not seem to be an issue. But i would like to know if the valve is malfunctioning or not. Thanks in advance.

Re: mercruiser water pressure relief valve question
 

Sounds like it is working fine. No flow at idle or low speeds. Not enough water pressure to override the spring pressure. Then gradually opens till full open as rpms pick up. I replaced my springs with a lower rating so mine open a bit sooner and then am max'd out at 20psi.

Re: mercruiser water pressure relief valve question
 

i'm no expert on the part, i was just thinking that the valve wouldn't pass any water out the relief output until it got to 25psi, then the relief would open, till then, just water to the sea water pump and that's it......... Where are you guys typically plumbing the relief output, right now, mine is teed into the bilge hose, i was thinking about putting another thru-hull water dump fitting just for the valve.

Re: mercruiser water pressure relief valve question
 

No, it starts opening before the 25 psi. Gradually opening. It's not a pop off valve as you are thinking like the saftey valve on your home water heater.

I welded a peice of 1" SS tubing into the outlet side of my silent choice divetor valves right behind the pivoting plate that I dump the water into. Didn't want to install any thru hull dump fittings.

Re: mercruiser water pressure relief valve question
 

If you don't mind a through hull dump a nice place to dump the water is on top of your drive cap. Help to keep the drive cool when running hard.

Re: mercruiser water pressure relief valve question
 

already has a drive shower, but thanks for the ideas

I'm digging this out of the archives to bring up again, as I still have some concerns with my water pressure and don't know enough about it..

I think the most water pressure that I've seen on my dash mounted gauge is around 10-12psi. I have the pick off from the thermostat housing running a wet line up to the guage. At WOT roughly 80mph is where i'm seeing this, and the pop off valve is letting quite a bit of water out. Does the pressure sound correct, or should there be a stiffer spring in it or something? I've never opened the valve so I do not know what spring is in it. Just always thought it was supposed to be a max of 25psi. Thanks for the support.

I've seen a handful of people talk about the proper install location of this valve, and have read a handful of different locations.

What is the proper location for a merc or any other manufacturer of water pressure relief valve in the system?

I doubt you are getting a true water pressure reading from the tstat housing.

What do you suggest? I figured pressure was pressure no matter where in the engine. I guess what I don't know is how the thermostat plays into the pressure tap on the housing.....