Finally got the hose cleaned out at the block.It was really clogged with silt.This was on my starboard engine and my port gauge now reads 7 psi at idle and pins 35 psi at 3000 rpm, higher then it did before.Is this too high for raw water pressure ?And also my hoses must be crossed some where because my starboard guage still reads the same as before 0 psi at idle and 7 psi at 3000 rpm.Now I need to clean out the port engine and check the routing of the hoses.What should the max pressure be and why would it be so high?

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You have basically no pressure at idle. That's normal. The 7 is low. double check the WP hose, sea water pump for correct hose connections and for broken impellor vanes.

"ideally' max pressure should be around 20*. I have the same high pressure as all stock BBC do aand will blow water past the seals in the wp at wot runs and into the bildge.

What controls the pressure?any way to adjust it?Still wondering why the other is much lower.I will check it out if the rain ever stops.

The pressure is derieved from the T-stat housing and the exhaust. I take it yours has the brass tee on the stat housing. Those were never a problem like the newer design. Merc makes a relief valve ( for a problem they say doesn't exist), but it doubled in price last fall. Something around $250ish.

I guess they realize how many people have the problem that doesn't exist. More profit!
Dan

I'm going to flush the system out and clean all hoses and change thermostats.Maybe its a stat hanging up or something.What would it hurt yo run at 35 psi?Probably head gasket right.I was also told the 502 should have heads redone about every 350 hours.Whats your thought?Motors have 535 hours now and run good.Just wondering if I should do them over winter or not.