1989 Crusader 454 problems. Need help.

So the mechanics start diagnosing the overheating by changing the manifolds and risers first?!? Then move on to the easier (re:less costly) items like hoses, impellars, etc?
Definitely get a second opinion after you get your yacht out of there. Buy a compression tester from Sears/Crasftman and test each cylinder yourself. Not likely all cylinders dropped 100 psi in a year. If you do get a low reading, then squirt some oil into the cylinder (not a lot, couple of squirts) and test again. If compression goes up, chances are you have a few busted rings (which could happen in several cylinders especially after sitting for 7 years, but does not explain the overheating).
If the block is cracked, typically but not always you get low compression in two cylinders right next to each other. Cracked head or block may dump antifreeze into oil or into cylinder where it burns and is billowy white at the exhaust (blue exhaust and probably burning oil, black exhaust signifies unburned fuel from various causes).
Do you know if they replaced the original risers? Is muffler aluminum or fiberglass? Aluminum will rust and give rust specks at the exhaust, had that problem on a Silverton with the 350 Crusaders.
Take hose off of the lower part of the oil cooler and make sure nothing is blocking the inlet (I think you can stick your finger up there).
Good luck.

similar issue but not quite the same

5.7 crusaders with heat exchanger and fresh water system is running hot and would overheat if we did not turn off the engine.

As part of trouble shooting we changed the thermostat and replaced the antifreeze and the impellers. After doing all 3 of these to both engines, one engine is fine and the other is still not fixed.

The heat exchanger itself is hot to the touch but nothing else seems hot to the touch. After running the motor I also do not feel hot water coming out of the tap.

What would be the next troubleshooting steps?

Thanks

Overheating Crusaders

To chase down an overheating engine requires a bit of patience. First of all, get yourself a digital infrared thermometer that you can point at various cooling components on the engine. You can get them at Grainger, Sears, an auto parts store, or your local truck jobber Snap-On guy. Take readings from cold start at your raw water intake, your raw water pump, heat exchanger at the middle and both ends, your intake manifold cooling ports that feed each head, your fresh water pump on at the hose, along the manifolds above each spark on both banks of the engine, then each riser top and bottom. Write these numbers down, then take them when the engines are warmed up. Next run the boat and let it get too warm, not overheated, and take the readings again at the heat exchanger, manifolds and risers. Check your oil coolers too, anything that flows water is suspect. Could even be your heat exchanger in the water heater for your fresh water on the boat. You never know. If You will find the rise in temperature infrared reading it will indicate the problem area. That is the component you should attack.

As far as compression, with universal low numbers, you could have a leaking head gasket on one bank or another. A cylinder leak down test will help you find out if it is the valve train, or the engine rings. Remember that the bottom end of your engine is nothing but a pump. Maybe a sticking ring at most. The valve train is a more likely source of power related issues.

Check the engine timing and dwell. Use a dwell meter on the distributor and look for a read in the 28 - 32 degree dwell range. Use a real timing light to check and set the timing. An over advanced timing can cause the overheat you describe, and if it is really bad it will burn a hole in the top of your piston. Don't advance it too much, and run the rpm's up in neutral to see how far your distributor advances the mark. You may have a bad mechanical advance that allows for too much spark advance. In your car you would hear this as knocking like on the wrong octane gas, but in your boat you may not ever hear it. Check that timing with a good light.

Finally, there is nothing wrong with carbs and conventional ignition. Easy to service and nothing too complicated to fail in the worst moment when running an inlet on an incoming tide. You may want to upgrade to electronic distributor for the lack of points to replace. But a good running carb engine is a reliable piece of equipment that you don't need $3000 in test equipment to find a bad $3 module.

Would appreciate you posting an update on this problem too.

Regards.

Our issue is solved

It turns out that one of the brand new thermostats was bad.

We were se to test it in boiling water.

We exchanged it for a new one and now it is not overheating anymore.