I have a 2005 29' Fountain with a 525 EFI. Water pressure is above 40 PSI over 4000 rpm. There's no blockage issue, and I'm thinking about installing pressure relief valve. Any one else install one? Any recommendations? Thanks!

Lots of people run them. 40 psi is too high. I have one pricy plastic mercrusier one, and a nice metal one from C.P. performance. There are a couple in the swamp shop. Cheap and easy to install, your only talking about hoses. Mine never go over 20 psi.

Mercury manual says you are OK up to 43 psi with the 525. I installed a pop-off valve on mine but have removed it. The 525 likes more than 20-25. I try to hold mine at 35-40 when running hard. I welded up and reshaped the inlet on the Imco shorty. If the pressure shoots too high I can lower it by bumping the trim up. If a relief valve sticks open on a hard run it could be disastrous. Brownie (Alan Brown) himself came onto a thread that I started about this same thing and advised against running a relief valve. With raw water cooling it is much more important to keep pressure around 20-25.

Yes the manual says up to 40 because they had problems cooling the headers when they first came out with the 525sc. Do a search on Water Pressure in the title, you can read the rest of the night. To much pressure and you can push water around the gaskets.

I use the merc relief valves. Come stock with 30 lb spring, should be plenty for most applications. I ran the exit hoses out the side of the hull, that way it is easy to check if they are working correctly. Working ok for 3 years now.

It's closed cooled. The water doesn't go around gaskets, it just flows through the various coolers. Mercury service manual says 43 psi max. Not up to 40. I regularly run 40 psi. This is an '07 vintage engine.

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