Exhaust manifold/risers/elbow question

[badrano]

I've been digging around the forum to what info there is regarding how long manifolds last in non-fresh water environments.

I've got a 2005 Chap 256SSi with the MX 6.2 MPI s/n 0W061713, Bravo 3. I've owned the boat going on 6 years and bought it with 160 some hrs on it. It was a fresh water boat and I mainly boat in brackish water. It's trailered and I haven't been consistent on flushing it after every use. Based on what I've read, I think I'm pushing the limit to where I need to start thinking (and saving $$) about replacing the manifolds and such. I have not had any cooling issues up to this point.

I've also read that I could start off with popping the elbows off to inspect the water passages. I'm assuming if I pop off the elbows, I will need to replace the gaskets. Can I re-use the bolts? I've read things where these bolts could become elongated if torqued down too many times. I've seen pictures of what the rust build up would look like, but I just learned that those pics were of wet joint elbows/manifolds. I have dry joint with 3in risers, so would I expect to see similar rust build up?

Any advice/suggestions? Probably more questions to follow.

 

[alldodge]

Guessing your open (raw water) cooling and not closed, correct?

Bolts can be reused provided they are fully intact and have not been reduced by rust. If bolts are over torqued they can be compromised, but assuming your motor has not been touched they should be fine

Yes have a look at elbows and do replace gaskets

 

[Lou C]

I would figure on using a thread chaser, solvent and compressed air to make sure the bolt holes are clean, or else you might not get adequate clamping force on the gasket. Merc's dry joint is a lot better about keeping water out of the exhaust than the older style wet joint though.

 

[Chris1956]

Pull the rubber sleeves off the risers and look at the place where the cooling water mixes with the exhaust. They tend to rot/rust out there first, in my experience.

In full salt water, risers/mannys tend to last 8 years of so. If you do remove the risers from the manifolds, clean up the mating surfaces with sandpaper on a glass plate. Also, be sure to use the silver Mercruiser gaskets. The thinner paper gaskets often fail

 

[Scott Danforth]

Pull the elbows and look

 

[Lou C]

I'd start by removing the rubber exhaust hoses (this can be quite the battle, sometimes harder than getting the bolts out lol) what you are looking for it this:
I'd think that given the difference in the Merc water flow for the dry joint vs the wet joint there might be a greater chance you can re-use the manifolds, but they should be tested by filling with acetone (careful, flammable).

not mine but saw this on the hull truth

 

[Chris1956]

Lou, The mating surfaces of the risers have the Merc gaskets on them, right? Those gaskets are for a 1/2 FWC cooled motor, yes?

 

[Lou C]

They do and can be set up either way.
there was a guy on this forum who adapted those to a V6 Cobra like mine and if they actually fit and worked well I might try them the next time I have to change manifolds/elbows which will be about 2 seasons from now. I've been using the OMC/Volvo 2 piece units since 2017 when I did the top end overhaul, but the dry joint is superior in terms of keeping out water.
I do use the endoscope camera to check inside each season so I'd know if water was getting in. A good maintenance practice.
You can get a nice pic with them!

 

[Chris1956]

In case someone does not know, a 1/2 FWC motor needs a heat exchanger in the boat to function. A raw water-cooled motor does not have a heat exchanger in the boat.

 

[Lou C]

True and if you want a full system including the manifolds, you have to make sure that the impeller in the outdrive or on the engine flows enough water volume to deal with the extra heat load of the manifolds.

 

[tpenfield]

I would do the inspection thing, because in fresh water the exhaust should last forever. Brackish might get you some deterioration.

 

[Chris1956]

The way I understood it was that a V6 or smaller FWC engine could be cooled by the outdrive pump, but a V8 or larger FWC engine needs a belt driven thru the hull water pump to cool the heat exchanger. Is that correct?