1977 ford 302 pleasurecraft exhaust manifold crack

I have a 1977 correct craft with a ford 302 pleasurecraft engine. It is fresh water cooled with a water pump. Why would the exhaust manifolds crack or split. One cracked on the water jacket one year and the other the next few years after that. I want to replace but what else is wrong. is the muffler or something else not working correctly.

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GeorgeLandis said:

I have a 1977 correct craft with a ford 302 pleasurecraft engine. It is fresh water cooled
This would be a Closed Cooling system.

with a water pump.
You'll see two pumps.
The Ford pump is an engine circulating pump. The other will be your seawater pump.

Why would the exhaust manifolds crack or split. One cracked on the water jacket one year and the other the next few years after that. I want to replace but what else is wrong. is the muffler or something else not working correctly.
We'll see two types of Closed Cooling systems.
A "half" system and a "full" system.
The half system will not include the exhaust manifolds, of which will remain seawater cooled and probably explains why they cracked if they had not been properly drained of seawater.

In either event, the exhaust elbows will remain seawater cooled.

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It is not a closed system. water is pulled up by a pump then goes into the engine cooling system, then is exhausted out the exhaust system in jackets in the exhaust. I am not sure if it was caused by freeze or by temperature of water being to cool on the hot exhaust manifolds, i am thinking the latter, since it was always drained in the winter but i suppose rust could let the water not drain completely. I am thinking maybe the thermostat was letting to much water into the cooling system and cooled the exhaust to quickly thus cracking them. Any thoughts? This is a fresh water system.

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GeorgeLandis said:

It is not a closed system.
My mistake.
You did say: "It is fresh water cooled with a water pump."
FWC is often use in a misnomer fashion to describe Closed Cooling.

I am not sure if it was caused by freeze or by temperature of water being to cool on the hot exhaust manifolds,
The manifolds will receive coolant (water) long before temperatures are up.

i am thinking the latter, since it was always drained in the winter but i suppose rust could let the water not drain completely. I am thinking maybe the thermostat was letting to much water into the cooling system and cooled the exhaust to quickly thus cracking them.
See above!
Also, most coolant will be by-passing the actual engine cooling demands and will be going out the exhaust system.

This is a fresh water system.
Meaning that you're operating in lake or river water... yes/no?

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