When to replace manifolds and riser/elbows?

[PoppyTortuga]

Here's what I have:
2004 8.1 Volvo Penta gas engines with heat exchangers. Engines have about 1,050 hours on them, 800 of which were fresh water until around October 2022 when I started down the east coast ICW from NY to Florida, so maybe 250 hours in salt water. Engines run rock solid, no issues.

The conversation/concerns:
Another 356 in my marina just blew an engine. Topic of conversation is "when have the manifolds and risers/elbows been replaced?" For my boat, never. From the outside all manifolds/risers look great. Several people are telling me it's not an "engine hour" item of concern but a "calendar" item. Stating all manifolds and risers should be replaced every 3-5 years max regardless of run time. I've done some research online, e.g., BoatTest article states 3-5 yrs as well (or I'm just asking for a blown engine repair). I don't have the expertise to take on a job this size and would need to have a mechanic do it. A quick quote was offered of $5,500-6,000. I know it's a lot cheaper than a blown engine, however, if I can hold off for another year or so while in salt water I'd do it.
What is your personal experience with replacing manifolds/risers on a VOLVO gas engine with heat exchangers, etc.? What condition was your manifolds in when you pulled them? Did you think, wow, they look great. Could have gone another 5 years? Or was it more like, damn, got to them just in time. What was your time frame, e.g., 3 yrs and replaced? 20 yrs? Or like my boat, never.

Thanks in advance for all your input.
Bob

[bud37]

One thing you could consider would be a fresh water flush system for your engines and manifolds.....done each time you return to dock, it may lengthen the time for you......until you return to fresh.

I believe changing out the manifolds etc is a maintenance item in certain boating areas regardless, unless you have a trawler with dry stack and keel cooler.....

[Midnightsun]

Tough call, expansion and contraction of metal does accelerate corrosion so running time does have some affect however I agree, calendar is a better way to determine when they should be done. The norm does seem to be 3-5 years in salt. Fresh water only applications on the other hand is not an issue, the elbows and risers will outlast the engine and then some.

[km1125]

First, you need to determine if your manifolds are raw water cooled or if the have engine coolant in them. If they have coolant, then they should be as OK as your entire block, meaning they don't have to be replaced. Your risers on the other hand, certainly should in that 3-5 year interval.

I'd say if you've only been in saltwater less then a full year you have PLENTY of time to figure out your move.

Are you coming back to freshwater, or is the boat staying in the salt life?

[km1125]

Oh, and I'm wondering why we didn't hear about this trip from the Finger Lakes down to FL?? (with some pics!!)

Sounds like a fun and adventurous trip! Did I miss the postings somehow?

[Viper]

You should be okay starting the countdown from when she first entered salt water, but given the vintage, I'd consider replacement at the lower end of the recommended scale for replacement. You need though to find out if the manifolds are raw water or closed cooled. If they are closed cooled (fresh water cooled/coolant), you'll only need to worry about the elbows and any other raw water cooled exhaust components.

[PoppyTortuga]

QR_BBPOST First, you need to determine if your manifolds are raw water cooled or if the have engine coolant in them. If they have coolant, then they should be as OK as your entire block, meaning they don't have to be replaced. Your risers on the other hand, certainly should in that 3-5 year interval.

I'd say if you've only been in saltwater less then a full year you have PLENTY of time to figure out your move.

Are you coming back to freshwater, or is the boat staying in the salt life?

I'm currently in brackish water, i.e., 25 miles up the St. John's River outside Jacksonville. So, that, and salt water when I cruise again. I doubt I'll see any fresh water with this boat ever again.

[PoppyTortuga]

QR_BBPOST Oh, and I'm wondering why we didn't hear about this trip from the Finger Lakes down to FL?? (with some pics!!)

Sounds like a fun and adventurous trip! Did I miss the postings somehow?

Ops! Sorry about that. However, you can find all my travels and posts on FB under "Poppy Tortuga".

[PoppyTortuga]

QR_BBPOST You should be okay starting the countdown from when she first entered salt water, but given the vintage, I'd consider replacement at the lower end of the recommended scale for replacement. You need though to find out if the manifolds are raw water or closed cooled. If they are closed cooled (fresh water cooled/coolant), you'll only need to worry about the elbows and any other raw water cooled exhaust components.

Yes, I was thinking the same. I was hoping for an answer to that question here on this forum. In the mean time I just found out we have a local Volvo shop which I'll be calling for that answer, and more. I remember the good ole days of BOAT, now it's BOATT (bust out another $10k).

[Viper]

QR_BBPOST ....now it's BOATT (bust out another $10k).

Ya pretty much