Exhaust cooling system

[NHGuy]

My boat is 22 years old, but I have only had it for 2 years. It allegedly spent it's life in fresh water, but you know how stories go. How do I determine how much to trust my exhaust manifolds and risers? I don't want to be the guy with water in the combustion chambers. How do the saltwater folks decide when to change them? I hope there is some way to find out when they fail without engine repairs. I read too many horror stories on here I guess.

 

[HT32BSX115]

Re: Exhaust cooling system

Howdy,


Fresh water risers and manifolds can last a "good long time".

If they're 22 years old, you should pull them, separate the risers and carefully inspect the sealing surfaces and whether they're clogged or not. (you'll need new riser gaskets of course)

If I had manifolds and risers that old, I would consider myself lucky I didn't destroy the engine and replace them!

How old are they?

 

[NHGuy]

Re: Exhaust cooling system

I had the risers off before I ever used the boat, they are fine, but I am seriously thinking of pulling the risers and manifolds for an acetone test this off season.
Or I might just buy manifolds as a maintenance item.
But again, how do you know they are bad? Do you wait for engine trouble? That seems kind of dumb. Who ever lives in freshwater only, how long have yours lasted?

 

[meesh]

Re: Exhaust cooling system

I replaced mine last year after 29 years in fresh water. The manifolds looked great, but the risers were thinning with a lot of rust scale flaking off in them. I fill mine with antifreeze when I winterize and I personally think it adds to their life. I know that will get a lot of arguments but I like the idea of added corrosion protection.

 

[cr2k]

Re: Exhaust cooling system

Just be sure to replace the riser gaskets with the same one in the same arrangement. Many have not paid attention to this and had temperature issues subsequent to riser removal.

 

[HT32BSX115]

Re: Exhaust cooling system

I fill mine with antifreeze when I winterize and I personally think it adds to their life.

I think you're right.

29 years is pretty good service for risers and manifolds.

but I am seriously thinking of pulling the risers and manifolds for an acetone test this off season.

That's ok. BUT, that only tells you if they are NOT leaking. It doesn't tell you when they'll start!!!

There's really no reliable way to tell how long you have until they start leaking.

AND when they start leaking........ they start allowing water into the exhaust area (where water should NEVER go)


The real problem is when 1 or more exhaust valves are open and you let it sit for an extended period of time. (like the whole winter)...........

THEN, (of course with "Murphy" laughing), you discover it next spring.....


I wouldn't go 29 years on a set of manifolds.........good luck on that.....


If there's a question on them......replace them. They aren't all that expensive....


Most exhaust/riser kits are around $500-600.....if you replaced them every 10 years, you're only talking about $60/year.


Probably less than the gas you put in the tank in an average couple of summer week-end trips!!!!!!!!!

 

[NHGuy]

Re: Exhaust cooling system

So very true. If they DO leak can one tell? Or do you end up with bent & broken engine parts from hydrolock?

 

[HT32BSX115]

Re: Exhaust cooling system

So very true. If they DO leak can one tell? Or do you end up with bent & broken engine parts from hydrolock?

Yes you can tell. From the hydrolock that is the result of water running into an open exhaust valve.

It doesn't always cause damage.

A few years ago my OMC 460 had leaking risers on both sides. It was the sealing surfaces (and gaskets) on both riser-manifold surfaces.

The (fresh-water only) manifolds and risers were only about 11 years or so old........but they had not been "broken" down and the gaskets replaced.

Every time I shut it down, it would "hydro-lock" if I tried to start it within 15 min or so....... The engine wouldn't completely crank over....it seemed like the battery was dead or the starter was failing.

If I let it sit more than about an hour after shutdown, The water would (presumably) drain past the rings and I could crank it right over.

It always started. The amount of water was small and since I ran the engine a lot, it never accumulated enough in the sump to cause a "milkshake" since the engine ran hot enough to completely evaporate all the water when running......and you do not get any water in there while the engine is running since it's blown out with the exhaust.






It did it all summer.


When I finally pulled the heads, it was quite evident that water had been sitting on top of some of the pistons and there was some corrosion on the cyl walls.

I think it sat more than a few winters with a little water in the cyls.


I was going to rebuild the engine when I found out that I couldn't buy manifolds (they don't make them anymore!!)

That's when I started looking for a replacement engine and drive....


Those manifolds were more or less ok but the sealing surfaces had started leaking..... The same thing would happen if the risers or manifolds began to leak.

My current engine is completely closed cooled. Anti-freeze is in the engines and manifolds now......but I still have raw water flowing though the risers......


You probably won't end up with broken or bent rods etc. The starter usually doesn't have enough power to bend a rod.....It'll just seem like the battery is dead or weak or the starter is failing......

You get bent rods from the engine turning fast and sucking water into the intake or during a reversion event.....


I would replace those manifolds and risers if they are really 22 years old.