496s with Bravo 3 with Sea Strainers. Condition: Low water pressure on Starboard engine. Ok below 1800 RPM, pressure will not go up above and the engine eventually overheats. Get a low pressure alarm. Changed the pump twice, New Hardin pump, then swapped with the Port side to verify I didn’t get a dud. Pump removed again, and backwashed system below the Heat Exhanger backwards and forwards with garden hose and compressed air. Took end caps off Heat Exchanger, clean as a whistle. The first time this problem developed it was after the boat was running about 3300 RPM for about 20 min, then bingo alarms go off. Now the alarm goes off as soon as I get it above 2000 RPM. I have Mobile VV and NMEA on the Chartplotter to watch the Gauges. Don’t think it is Bravoitis because I had this problem on the garden hose to eliminate that as an issue, plus everything I read is it should be more gradual overheating, not a overnight problem. May 15 I had 14.7 on Pressure. Sat Afternoon 10.8 (alarm and overheat never happened) Sunday morning after running 3300 RPMS for 20 min alarms and overheat 9.3 psi, Now it will not go above 4.3 when I bring the engine up above 1800 RPM. This is all in the course of 3 days. My next thing to check is those Ball Check Valves under the Exhaust Manifolds. Has anyone had any experience with those failing?

Are the tops on your strainers nice and tight? I've seen a loose top cause pressure problems.

Yes, even ran the engine on the garden hose bypassing the strainer with a flush kit I install to the intake hose I pull off the strainer. They are real tight.

Are you getting a decent water flow out of the exhaust when running on the hose? Is it pouring out? Low pressure doesn't necessarily mean lack of water flow.

Those balls are too let the water drain slowly when the engine is turned off to to help with heat after shut down. I don't think that would cause any issues if they were not working properly.

Say the ball is missing or not closing when the engine is running. Would water escape up to the manifold and out? And then causing an overheat because not all the Water is making it to the Heat Exchanger? Low Water pressure since the water is escaping thru a “hole” in the system now? Also if it is the Stbd Manifold the check valve allows water to escape before it gets to the pump. Just curious if anyone has experience with problems with those check valves and what condition was created by a failure.

Hard to tell with the boat in water. I did pull the hose off the fuel cooler to the heat exchanger on both engines to compare water flow coming out the fuel cooler and there was a noticeable difference when I reved the engine.

Say the ball is missing or not closing when the engine is running. Would water escape up to the manifold and out? And then causing an overheat because not all the Water is making it to the Heat Exchanger? Low Water pressure since the water is escaping thru a “hole” in the system now? Also if it is the Stbd Manifold the check valve allows water to escape before it gets to the pump. Just curious if anyone has experience with problems with those check valves and what condition was created by a failure.

Found this after a quick search on the forums:

That will tell you if the ball valve is causing the overheat.

The ball could be gummed up with debris and not letting water flow from the drive to the engine. I've seen it happen. Just remove the ball. It's not needed.