Inboard exhaust manifold question

[aldo]

I have a fresh water cooled 350 inboard installed in 1995. I changed the risers 4 years ago but never the manifolds.
The exhaust manifolds are getting flaky with rust.
Time to change them?
Does salt water pass through these or just the risers?
Thanks.

[ggreeby]

You will find there are 2 types of fresh water cooling. 1 is called a 1/2 system, that uses raw water to cool manifolds and rizers . 2nd type cools only the rizers with raw water. Find either a good photo of both plumbing systems ,or find a person who knows by looking which system you have. DO NOT CHEAP OUT ON MANIFOLDS OR RIZERS. George

[Islandtrader]

You will find there are 2 types of fresh water cooling. 1 is called a 1/2 system, that uses raw water to cool manifolds and rizers . 2nd type cools only the rizers with raw water.

I am not sure that is entirely correct.

There is a raw water system that cools the entire drive drain with the water that the boat is in.

One system (lets call it the 1/2)cools the engine block and intake manifold with a closed (fresh) water system. Raw water then cool upper and lower exhaust and risers.

The other type of system like Crusaders and Merc Sea Core uses a closed (fresh water) to cool engine and all risers.

However I agree don't cheap out...

[aldo]

I'm sure some where along the line the fresh water is cooled by sea water. Sounds like I will be changing them this winter.
Thanks for the advice.

[BigLew]

Sounds like it might be the optimum time to up grade to a full Fresh Water system. It may be more cash now, but given the longer life offered by the "full" system and that fact of life that costs simply seem to always go up, it isn't going toget any cheaper.

Just my 2 cents.

[aldo]

Did some home work. No raw water in the manifolds on this system, so the rust is from the outside only. Worst case is blowing a hole and exhaust out the manifold. I'll give it a closer inspection when I pull it out this week-end.

[ggreeby]

All fresh water cooling systems use some sort of heat exchanger ( fresh water to raw water ) . The 1/2 system cools The Engine complete. The full system cools the Engine plus exhaust manifolds , but not the Risers . The risers are raw water cooled thay is where the water to keep the rest of the Exhaust system Temp safe, and discharge the Raw water. George

[ggreeby]

All fresh water cooling systems use some sort of heat exchanger ( fresh water to raw water ) . The 1/2 system cools The Engine complete. The full system cools the Engine plus exhaust manifolds , but not the Risers . The risers are raw water cooled that is where the water to keep the rest of the Exhaust system Temp safe, and discharge the Raw water. George