Exhaust manifold - FWC service life

[Skipper]

Howdy,

I read in Boat U.S.'s mag something about an exhaust manifold lasting only 3-5 years in salt water. They mentioned that (paraphrasing) if the manifold is visibly rusty on the exterior, then the interior should be suspect.

However, I don't recall their differentiating between fresh water cooled and raw. Should we be equally concerned regarding a FWC manifold? I would think not; seems the manifold would wear the same as the engine circuit. Also, my 28-year-old Universal M-18 manifold is well rusted on the exterior, mostly I think from a previous lethargic cap, but the coolant looks and smells like it just came from the coolant factory after 10 - 15 hours (7 months including winter layup) use.

Should I be looking at a new $700 manifold based on age and extrior rust? Sideline: Luuuudicrous ripoff for a hunk of metal with no precision or complexity to build. I mean, it's 10% of the cost of a WHOLE NEW ENGINE - IE: Beta 16.

 

[Tim R.]

Not true. A manifold can look awful from the outside and be sparkling clean on the inside if properly maintained.

The combination manifold/HE on my Yanmar looked new on the outside but corroded a pinhole between the fresh and raw water sides after 14 years and roughly 2000 hrs. Although I bnelieve this to be a design defect as the wall was too thin. The replacement had a wall double the thickness.

 

[kloudie1]

From the article, http://www.boatus.com/boattech/articles/exhaust-manifolds.asp
It sounds like they are talking V-8, sea water cooled.. You can inspect a little of the inside on most engines by looking inside the header tank under the "radiator" cap. My Yanmar fresh water cooled exhaust header is fine at 27 years of age. It gets new coolant every couple of years. The "riser" that they talk about is the elbow where the sea water and hot gases mix. This does corrode and needs cleaning/replacement, especially if operated in salt water. Many posts on this site .. Mine was about 10 years old whenn it corroded through.

 

[Stu Jackson]

BoatUS has been writing that for the past twenty or more years. I, too, was concerned, as you are. But after doing some research, I concluded that they have never differentiated V8 engines in mobos from the exhaust manifolds on our small diesel engines. Kloudie and Tim are right.

That said, what DOES go south on our diesels is the exhaust RISER where the hot water from the heat exchanger meets the hot exhaust gas before the water lift muffler. BoatUS hasn't said much about that, have they?

 

[bria46]

I've had my exhaust system checked by an engine mech. He said that the manifold looked the same as the day my Westerbeke 10-2 was installed. Oh, It's a fresh water boat!

 

[Skipper]

Thank you

 

[tommays]

On a saltwater cooled inboard based on a car block 95% of all boats manifold life is SHORT if it used in saltwater full time

Trailering and flushing with freshwater they will last almost forever as these were 12 years old when checked in these photos

Powerboats have tried all kinds of flap valves to stop water ingress into the cylinders and a properly installed motor with the elbow at the correct height above the waterline still works better

 

[Stu Jackson]

Here's ours in 2008, 1986 boat. Pretty clean even before prepping for the new riser and "green" Universal gasket. We'd just taken the exhaust riser off.

M25 engine, around 2,000 engine hours. On our diesels, it is NOT the manifold, it is the riser.

If the boat is freshwater cooled with a HX it don't make no diff'rerance mon, 'cuz the stuff that goes in the manifold is FRESH coolant.

I have yet to understand the "different" issues on fresh water or salt water sailed boats, when it comes to these kind of things.