Gas engine exhaust manifold compare

[Aj325]

I had come to the realization that I probably misstated my configuration. My engines are "raw", seawater cooled, they are NOT closed systems with antifreeze providing the cooling. Therefore my exhaust manifolds are susceptible to corrosion and plugging with deposits of lime and whatever, along with the risers and elbows. The only positive is the boat has always been operated in fresh water.
km1125's comment about no visible problems in the manifolds is somewhat reassuring until you factor in that mine are for sure 13 years old, but could be 25 if original!
KM1125, did you replace the risers and elbows at the same time as the manifolds? Is there any way to inspect these components after removing them? Or, are the internal passages totally inaccessible?

[tomschauer]

If you have a cracked manifold, it either overheated or froze. Either one not good.
Make sure you are not getting any water in the oil, which could indicate a cracked block.
If your good there, you of course need to replace at least the manifold and riser that is cracked. If you had no overheating problems while underway at cruise speed, you may be able to buy one manifold and one riser. Pull the old off and look at the condition of the passages. If they have a heavy calcium/ lime build up, order the others and do them all. Manifolds and risers aren't cheap, but they do cost significantly less then a new engine with new manifolds and risers.

[km1125]

There are two conversations going on in this thread which can cause some confusion. The OP had a cracked riser, but later AJ325 asked a related question.

QR_BBPOST I had come to the realization that I probably misstated my configuration. My engines are "raw", seawater cooled, they are NOT closed systems with antifreeze providing the cooling. Therefore my exhaust manifolds are susceptible to corrosion and plugging with deposits of lime and whatever, along with the risers and elbows. The only positive is the boat has always been operated in fresh water.
km1125's comment about no visible problems in the manifolds is somewhat reassuring until you factor in that mine are for sure 13 years old, but could be 25 if original!
KM1125, did you replace the risers and elbows at the same time as the manifolds? Is there any way to inspect these components after removing them? Or, are the internal passages totally inaccessible?

I did replace everything at the same time as I had no idea of the condition. I was "pleasantly surprised" to find no issues of concern on the old parts, even though I just spent quite a bit of $$ on new parts to replace them. You can do some visual inspection but you'd really need some better equipment to totally 'absolve' old manifolds of any issues with wall thickness.
When I look at the total number of years and hours we put on the boat, those costs were pennies in the overall scenario and completely removed one of the worries in running the boat.

[Cooler]

Aj325 - Are you having any problems that is causing this concern? If the vessel has been in your area on Lake MI it's whole life, then I doubt you have any concern for excess deposits, etc. I am familiar with the water condition in your area, and while considered hard water by normal standards, you are running in clean, fresh water. Like Viper said, a slight difference in temp to the touch is normal. If you need any guidance, Tom at Accurate Marine in Kewaunee is really good and could provide some assistance. Just a few miles north of you. Good luck! er

[buster53]

QR_BBPOST

QR_BBPOST Buster53 wrote:
"If you have a full fresh water cooled engine, you will probably never replace the manifolds, only the elbow/risers."
Would you please explain a bit further on this comment....

If it's "full fresh water" cooling, that means the manifolds are cooled with antifreeze and not subject to the rusting you get with raw water. The elbows/risers are still subject to raw water, so they would need to be replaced at some point.

With antifreeze running through the manifolds, they should last the life of the block from the standpoint of rust and corrosion.

[Dewmyster]

Just as an FYI - Mercruiser manifolds are not included in the "closed" cooling system. As far as I know only Crusader are.

[tomschauer]

Mercruiser manifolds on a closed cooling system are also cooled with the antifreeze/ engine coolant. Only the risers and elbows are exposed to the raw water.

[Viper]

Ya all brands have the full closed cooling option that includes exhaust manifolds. It's not a complicated difference from a raw water cooled manifold, usually just a gasket/block off plate depending on design.

[Aj325]

Cooler, No issues that I am aware of, just the unknowns of a used boat and the fear of damaging the engines if a faulty manifold leaked water into an exhaust port. I have a long to do list for this year with associated costs so I know I won't get to this PM until at least next year. Thanks for the lead to Tom at Accurate Marine, I will contact him to discuss. Look forward to meeting you sometime. Do you ever make Sturgeon Bay a destination?

[Cooler]

Yes, I do go to Sturgeon Bay a bit. Not crazy about dealing with no-wake areas and the bridges. I am almost always 5 or 10 min late for the opening at Mich St. Fish Creek much more often. Only 17 miles from my home slip in Menominee and no speed limited stretches. That plus Peninsula Park is just beautiful to anchor in. The smell of camp fires, pine trees, and bacon is always beckoning me. The municipal marina at Fish Creek is great for dock walkers, and great pizza & chili 500 feet from the marina. If you see me in Door County, you will know it's me. Just look for the . Can't miss it. er