Rebel Heart, In my experience 12 lbs at wot is dangerous in motors without closed cooling. That is not enough pressure to keep air pockets from forming in your heads. Your temp sender reads the front of the motor and is not a tell all reading. Careful. I hope some one else chimes in here.
Jim

The Merc releif valves get it at a constant 25lbs

I know the engine builder cut the spring back so there would be less pressure. Should I have another spring installed to run more pressure? We were having trouble with water getting into the engines because of the pressure. I know he did go with a different gasket that corrected that problem, but most of the time the PSI only reads around 10 when cruising.

with out a doubt . 12 is way to low. w.o.t should see atkeast 20. i have found if you plumb a pop off valve in at the strainer you end up with more stable water pressure. or in the least a bleed off , if not both.
if you have a new style mercury package then you may put the engine in guardian with such low pressure.

How should this work with an intercooler that pumps thru the hull? My motor never gets hot, but I don't see any pressure until I'm on plane. Then, it's usually 5-8psi

Would this work?
http://www.hardin-marine.com/detail~ID~502.aspx
Are you placing it on the inlet or outlet of the strainer?

Dennis

How do I remedy the situation? Just buy another spring and leave it alone since it is automatically set at 25? Appreciate the repsonses, as I don't want to put the engines at risk.

that would be it.

if that will remedy your situation with out being too involved then yes.

Presently I believe the stainer has a 1/2" NPT female fitting on it which I use to run freshwater flush.I could replace with the popoff tied directly into the strainer and regulate pressure through the strainer.Simple enough..........