Last yr I bought my Fountian for a reasonable price because it didn't have the original motor in it. It ran fine but I went through and rebuilt it over winter. The boat did NOT have a sea strainer or an oil cooler or oil temp sending unit. I added a Hardin sea strainer and a oil temp unit. I also replaced the water impeller. First time out my water press was over 35-40 psi and did cause a gasket to fail. Not sure where yet but the oil is getting water in it and Im the in process of fixing THAT problem now. Is the high psi do to NOT having an oil cooler on it? I know it should have one anyways BUT if I buy one will it fix my problem?!?! I read on other forums about a relief valve but they aren t cheap. Any other options? I just have a gen VI 502 w/ a bravo 1 XR lower.

Look back in the old swap shop ads. Somebody had relief valves for $65 each.
You need an oil cooler, but I doubt that has anything to with the high water psi.

How much water pressure is to much??

525's with closed loop book says max is 43 PSI
Most say 30 is pushing it
15-20 is what I like.
It is about a balance of water pressure and temp period. If you have the pressure and temps you want in each area, flow & Temp and should be fine. A sign of possibly not enough water flow is low water pressure or high water temps. For low pressure, first try restricting the exits at the tail pipes or water dumps to boost the pressure. When you get the pressure right, what is the water temp? Is the water pressure 15+ lbs and the water temp still high? If so, now is the time to work on more water flow. Bottom line, if your water pressure and water temps are acceptable, you water system flow is adequate.

Use a pressure relief valve, you can cob up your own very cheap at the hardware store. just install a t with the valve and dump it overboard.
Steve