4.3 Water in cylinder 4

[Gutie04]

Okay, new to me 1900SR with Mercruiser 4.3(carb) Alpha(1 I believe).

Engine ran great on a 30 minute sea trial. 2 successful boat days. Then starting having some starting troubles and would die when pulling back to idle or when putting into drive sometimes.

Took it out of the water. Freshwater rinsed just fine. Put it away for a week til I had time to play with it. Took it out and got an engine alarm 10 Minutes after start. Found, thermostat was bad. Replaced it. But when I attempted to start, it clunked and didn’t turn. Checked electric all good(battery @12.7V). Tried again, It surged slowly several times then started eventually. Wasn’t normal, so I pulled the plugs.
After inspection I’ve got water(salt) in Cyl 4 and in the oil pan. Manual says to change oil, run it and check for water again, but I’m leaning towards a new engine and my mechanic seems to agree.

Any recommendations would be appreciated.

If I have to get a new engine can I upgrade to a 4.7 or 5.0?

[mmwjr]

The exhaust is water jacketed and cooled. For salt water use they typically need to be replaced every 5 years due to corrosion which will allow water to get back in through the exhaust valve. I would inspect the exhaust and perform a compression test on the engine. A blown head gasket or cracked block or head may also be the source.

Not sure what a 4.7 is but either a 5.0 or 5.7 may fit it there is enough room in front of the engine box.