JJONES

At speed does the raw water pump do anything?I am going to install relief valves and am trying to figure out if I should install them before or after the pump.It would be great to install them at the sea strainer which seems like they would work because the water is at pressure as soon as it enters the boat but does the pressure increase because of the pump at speed.Thanks

1CE

Most pressure relief set ups are installed @ the sea strainer because @ high speed press. can become excessive, what is your water press. @ WOT anyways ?

JJONES

At idle or threw the harbor its roughly 5 psi but when on plain 35 to 40 psi or more!I plan on installing relief at the strainer.Does this sound good?

fastlane40

I think if installed before the pump you would have issues with the pump sucking air at lower speeds.I thought all reliefs were after the pump for that reason.

MM1

Drill relief holes in your thermostat and you won't have to plumb in anything else to your boat.

1CE

merc. marine likes 30-35 lbs. max. your on the high side put your pressure relief in the strainer. The pump can't suck air the blow off valve it is set in the closed position and only opens when the set relief pressure is exceeded. good luck, J ps the idea here is to prevent excessive water press. which could blow intake manifold or head gaskets etc.

JJONES

Thanks 1ce,THat was the plan,just wanted to make sure.

fastlane40

Sorry Jonesy i was thinking bleed off instead of valve.

1CE

correction news report update from MERC. likes 25-30 psi max.

ROTAX454

Can the Merc raw water pump (at 5K plus rpm of the motor) exceed the 25-30 psi to the motor? If so, does the merc racing relief valve be better installed between the pump and the motor? That way the motor is completely protected from any spike in water pressure?