This is the Gary Grimes solution to my water pressure woes. A tee fitting just after the coolers allows water to run to the transom mounted pressure relief valve. When the pressure starts to rise a spring allows a piston to uncover two ports that allow water to flow out the transom. My top water pressure is 24 lbs. Not the 40 + I had before. I have no idea why I had this problem but this is the fix.

Dan

This is a shot of the whole system. Sorry for the boring power. I hope to change that real soon.

TTT

Where does your pressure guage tap in to the engine at? I am rigging my 47 and I dont know where the factory hose usually hooks up. Also where did you get the pressure relief valve at?

Dan, you still had this problem with the non merc exhaust? I see Gils or Stainless exhaust. So that to me would make me believe the problem may be in the newer style stat housing as you mentioned once before. ????????
Has anyone tried the old style stat housings on the merc cast iron exhaust and made use of the plugged NPT fitting on the iron riser for the 2nd set of stat hoses that are not used on the new style housing? Seems like that could help with the problem of leaking past the manifold to riser gasket that seems to be less than desired. Less pressure going thru it. And do I recall that your fix was something like a $650/motor cure?

Thanks for bringing this back TTT. This is SO what I did not want to screw with again.


Jerry

I keep trying to forget that part. What I did was way over kill but I just wanted to be done with it. The problem has got to be the thermostat housings unless something was changed in the way water circulates through Gen VI engines. Merc has a shinny new part available to supposedly solve high water pressure issues. http://www.mercruiserparts.com/partsByNumber.asp

I guess Mercury is sort of admitting that they have a problem.

I had two problems with my boat. I was sucking air into the system over 60 MPH. My water pressure only got to 32 lbs before it started to drop. It would drop to 10-15 lbs at wot. I never had a water pressure gauge on my other boats so I didn't realize this was wrong. I figured Fountain sweated the details so I wouldn't have to, WRONG! OSO taught me that I had a problem. Not to mention the blue on the exhaust risers. I fixed Fountains problem by buying new drives with the dreaded Low Water Pick ups. First time out with the new drives I buried the 35 lb. gauges. The water pressure didn't drop at 60 it continued to build. Problem one solved: I wasn't sucking air any more.

I gave up on the incompetence of Mercury, the black engine division. I turned to the board for help. Gary Grimmes seemed like the only guaranteed solution. I wanted to buy the Mc Master Carr relief valves but wasn't convinced they would be able to flow enough water. Gary had me rule out my exhaust as the pressure point before he would consider selling me his valves. I teed off the thermostat just before the hose went to the exhaust and ran two hoses back over the transom. Dumping the water over the transom I still couldn't reduce the pressure. This proved the pressure was building up in the engine and not from restrictive exhaust. Putting the valves on was a band-aid fix to my problem but the results are fantastic. I run at lower oil temps almost to the point of needing an Oil thermostat. The water pumps don't weep, the hoses don't look like there going to explode, the engine still runs at the correct temp, and the exhaust risers don't heat up.

Dan

Fountain taps off the block drain on the port side of the engine block. I would check out Mercury’s relief valve first if your pressure isn't too high. I don't think there were too many issues with high pressure on the 500efi's.

Gary's dump valves were designed for race boats having pressure spikes when they re-enter the water at over 100 mph. The boats would see 80+ spikes of water pressure. It caused hoses to blow off and worse yet gaskets to fail on his race engines. The valves are his design. They are a very simple piston with a spring that opens up a 1 1/4 " opening to dump a large amount of water quickly. If you need his number let me know. There are a bunch of posts about high water pressure in the tech section also.

Dan