Risers and manifolds at the same time?

[jonny rotten]

Why are they usually changed at the same time?
If there is no water in the manifold shouldn't it last far longer than the risers?
Is it just because of where they mate together being rusted out or corroded?
If that area is good do they need to be changed out with a riser swap?

 

[Scott Danforth]

If you are in fresh water, they last forever

If you are in salt water, they last until the mating surface gets rusted away

Inspection will tell you if replacement is needed or not

 

[tpenfield]

Why are they usually changed at the same time?
If there is no water in the manifold shouldn't it last far longer than the risers?
Is it just because of where they mate together being rusted out or corroded?
If that area is good do they need to be changed out with a riser swap?

There will be either raw water or coolant in the exhaust manifold.

A FULL Closed Cooling system will have coolant in the manifolds. HALF Closed or RAW WATER Cooling will have the ocean/lake water in the manifolds.

So, if you are running a Raw water or Half closed system (in salt water) there will be deterioration at the mating surface of both the manifolds and the risers. Therefore you would be replacing both at the same time.

With a full closed cooling system, it would be just the risers.

 

[Lou C]

And in either system the elbows deteriorate faster because they are partly full of water but not fully like the manifolds. The air gets at damp surfaces at the end of the elbow and corrosion there is usually the worst. As noted the sealing surfaces especially on wet joint systems often gets rust pitted & won’t seal even with new gaskets.
I coated the sealing surfaces on mine with gasket sealer before installing so I’ll see if that kept the sealing surfaces from corroding when I take em apart to check.
In the past I have filled the manifolds with acetone to check for internal leaks. In my boating area I have heard of people just changing the elbows at 5/7 seasons as long as the manifolds pass the leak test & the sealing surfaces are good.

 

[tank1949]

Why are they usually changed at the same time?
If there is no water in the manifold shouldn't it last far longer than the risers?
Is it just because of where they mate together being rusted out or corroded?
If that area is good do they need to be changed out with a riser swap?

It has been my experience in salt water only! Cast Iron risers go first: 4-6 years. In many cases when inspecting, you can notice wall thickness reduced on manifolds where they mate with risers. Remember, the block and heads are rusting too. If you get 10 years on a salt water block w/o flushing, you are living on borrowed time. I once had a head rust through and lock the engine. I pulled heads quicky but notice block's water passage was restricted with too much rust. I replaced motor. Salt and iron don't play well.

 

[jonny rotten]

It has been my experience in salt water only! Cast Iron risers go first: 4-6 years. In many cases when inspecting, you can notice wall thickness reduced on manifolds where they mate with risers. Remember, the block and heads are rusting too. If you get 10 years on a salt water block w/o flushing, you are living on borrowed time. I once had a head rust through and lock the engine. I pulled heads quicky but notice block's water passage was restricted with too much rust. I replaced motor. Salt and iron don't play well.

It's in salt water but I trailer and flush as soon as I get home religiously since day one. It's a 32 year old 4.3 but was fresh water only till I got it 10 years ago.
I don't even want to think about needing a new motor. Would be game over for the boat

 

[Lou C]

If those 1988 batwings are original even with flushing you’re on borrowed time. If your keeping the boat consider the upgrade I did 5 years ago, Barr 2 piece layer style exhaust

 

[Lou C]

After 10 years in salt even with flushing I’d want to at least inspect those & do the acetone test. Bad manifolds are the #1 inboard engine killer because they look fine on the outside but…
It’s REALLY a shame to lose an other wise good engine over that.
On the batwings the cast iron between the water passages & the exhaust gas passage just isn’t that substantial. The 2 piece units I installed 5 years ago have a lot more material there…

 

[Lou C]

top pic is batwings....look at the wall thickness of the cast iron between the water passage and the exhaust gas passage, left side is new right side is after 5.5 seasons in salt water...
now look at the wall thickness of the 2 piece manifolds in the bottom pic....

 

[tank1949]

top pic is batwings....look at the wall thickness of the cast iron between the water passage and the exhaust gas passage, left side is new right side is after 5.5 seasons in salt water...
now look at the wall thickness of the 2 piece manifolds in the bottom pic....
View attachment 370115View attachment 370116

You nailed it! I wished SS risers worked and were reasonable $$$ for my antifreeze cooled V8 motor.

 

[jonny rotten]

top pic is batwings....look at the wall thickness of the cast iron between the water passage and the exhaust gas passage, left side is new right side is after 5.5 seasons in salt water...
now look at the wall thickness of the 2 piece manifolds in the bottom pic....
View attachment 370115View attachment 370116

Mine is a 2 piece wet riser/manifold. I haven't heard the term batwing before. Is that a one piece riser manifold?

 

[tpenfield]

You nailed it! I wished SS risers worked and were reasonable $$$ for my antifreeze cooled V8 motor.

My Formula 330 had the SS risers (elbows) and the iron manifolds, with closed cooling. So the coolant ran through the manifolds and the sea water ran out the SS risers . . . worked great and lasts forever (ie a long time)

 

[Lou C]

Mine is a 2 piece wet riser/manifold. I haven't heard the term batwing before. Is that a one piece riser manifold?

Yes that’s the one piece used from 1985-1990. 91 and up they went to the 2 piece units that both OMC & Volvo used.
Looks like you got the first run of the 2 piece set up which is good because if you need to replace you can just get a Barr Marine aftermarket kit for like $725 or so…
10 years of salt water use you got your moneys worth. Any leaks or rust trails coming from between the manifold & elbow?