Exhaust hose burn thru

[R-and-R]

Burned thru the exhaust hose on the starboard riser, starboard engine today. Pics below. It appears to be an actual burn through, not just age-related failure.

Engine temperature was normal.

Any thoughts on how/what would cause it?

2002 340 Dancer. 8.1s engines. ~ 700 hours

 

[scoflaw]

Not enough water

 

[velooce]

You have a water blockage reducing water flow most likely a piece of your impeller stuck in a cooler, transmission etc

 

[Zim]

Water blockage ...and thus causing it to run hot.

 

[R-and-R]

Thanks guys. I suspected impeller problem, but the normal engine temp threw me off.

 

[Jimmy Buoy]

I had the same thing 10yrs ago when getting my current boat. There must be enough water flowing through the heat exchanger to cool the engine's closed system, but in my case the exhaust manifolds were substantially blocked by corrosion. Raw water pumps were fine.

 

[R-and-R]

I had the same thing 10yrs ago when getting my current boat. There must be enough water flowing through the heat exchanger to cool the engine's closed system, but in my case the exhaust manifolds were substantially blocked by corrosion. Raw water pumps were fine.

Good point, thanks. A dock neighbor of mine mentioned exactly the same thing yesterday.

I've only had the boat about 2 months. I know the manifolds are not original, but I don't know when they were replaced. How did you analyze the problem to figure out what was causing the insufficient water flow?

I'm pretty mechanically inclined and thought replacing the impeller would be an easy and inexpensive first step. But about 30 minutes in, I realized I was getting in over my head, so now I have to wait for my mechanic to respond to my pleas for help.

 

[northern]

If you buy a spare raw water pump it will probably be the same cost as getting a mechanic to change the impeller. Rebuild it when you have time. Lots of utube on how. Then take the rebuilt one and put it on the other engine.
As to risers plugging off, it takes mine 3 years before I see white smoke (stream) in the exhaust and in the 5th year it last a couple of minutes. When that happens I replace the risers. They are not fully blocked but have a lot of rust in them and the cast iron looks good but when hit with a hammer it easily chips at the matting faces..

 

[Handsome Transom]

Our of curiosity was it the port side exhaust hose? I recently changed mine along with the butterfly valves at the y pipe and while I was at it I changed all the distribution hoses as a matter of maintenance not because of failure. Anyway the molded 1" hose on the port side that goes from the t stat housing to the water portside manifold was going to be a backorder so I replaced it with new 1" heater hose and made it ling enough to do a gentle curve instead of the molded ones 2 90degree bends .i used ed a pipe securement to the bulkhead to makevsure it stays . in place I was pleased because my risers are now equally cool while prior to this change my portside riser was noticeably hotter to the touch..
I also wonder if it would be less money in the long run for guys who run in salt water to just go with aluminum manifolds and risers.

 

[R-and-R]

Our of curiosity was it the port side exhaust hose? I recently changed mine along with the butterfly valves at the y pipe and while I was at it I changed all the distribution hoses as a matter of maintenance not because of failure. Anyway the molded 1" hose on the port side that goes from the t stat housing to the water portside manifold was going to be a backorder so I replaced it with new 1" heater hose and made it ling enough to do a gentle curve instead of the molded ones 2 90degree bends .i used ed a pipe securement to the bulkhead to makevsure it stays . in place I was pleased because my risers are now equally cool while prior to this change my portside riser was noticeably hotter to the touch..
I also wonder if it would be less money in the long run for guys who run in salt water to just go with aluminum manifolds and risers.

This was the starboard hose. Our surveyor shot the risers with an IR camera and all four appeared temperature balanced. I'm more inclined to think it's a recent development...possibly due to a recent shallow water encounter.

Interesting thought about aluminum replacements. One blog writer I saw regarding risers and elbows was pretty adamant about sticking with iron.

 

[R-and-R]

If you buy a spare raw water pump it will probably be the same cost as getting a mechanic to change the impeller. Rebuild it when you have time. Lots of utube on how. Then take the rebuilt one and put it on the other engine.
As to risers plugging off, it takes mine 3 years before I see white smoke (stream) in the exhaust and in the 5th year it last a couple of minutes. When that happens I replace the risers. They are not fully blocked but have a lot of rust in them and the cast iron looks good but when hit with a hammer it easily chips at the matting faces..

I like the spare pump idea...

 

[dwna1a]

Spare pump is the way to go. I purchased a new one and rebuilt the old bronze pump. You can find kits online.

Port failed first....6 weeks later the starboard. It was good to have the spare

 

[scoflaw]

He probably has the plastic pump. Forget the rebuild if so, they are cheap, buy a new one.

 

[Jimmy Buoy]

Good point, thanks. A dock neighbor of mine mentioned exactly the same thing yesterday.

I've only had the boat about 2 months. I know the manifolds are not original, but I don't know when they were replaced. How did you analyze the problem to figure out what was causing the insufficient water flow?

I'm pretty mechanically inclined and thought replacing the impeller would be an easy and inexpensive first step. But about 30 minutes in, I realized I was getting in over my head, so now I have to wait for my mechanic to respond to my pleas for help.

In my case, the boat was from Florida and had the original cast aluminum manifolds. Upon close inspection it was clear that one of the manifolds had been leaking seawater from a pinhole on the outside, so I decided to replace all four manifolds. Only after removing them did I see the full extent of the corrosion on the inside water channels on all of them. It was hard to believe that there was enough cooling water getting through to prevent the engines from overheating they were that restricted with aluminum oxide. Since I'm boating in the Great Lakes (fresh water) they were replaced with OEM Aluminum Manifolds which should last indefinitely here, but salt water really did a number on the cast aluminum (even with Merc's special black paint process). That's why they switched to cast iron, but they still have a limited life span in salt water due to build up of corrosion inside the water chambers.

As far as getting over your head, I wouldn't sell yourself short. The water pumps are usually not too bad a job, but with your engines facing backwards you may have to take off an exhaust tube to gain access. There are posts/photos of the job here on CSR if you do a quick search. The biggest job is getting the pump out and back in. I can usually have this done within an hour (including impeller replacement) now that I've done it a couple of times. Just take your time if you think you'd enjoy being able to do it yourself!

 

[R-and-R]

Finally circling back around...with positive results.

In the end, I did not replace the seawater impeller/pump.
After a lot of reading here and elsewhere and discussion with some dockmates and my mechanic, I suspected that the problem was a shallow-water mud encounter earlier in the day.

First, I replaced the offending exhaust hose. Then cleaned out the sea strainer. Using my newly purchased SeaFlush funnel, I turned over the engine just enough to verify that the pump was drawing water. From there, I disconnected the dripless and heat exchanger hoses and again turned over the engine to make sure I was getting output. Reconnected those and then started the engine (still using the seaflush) I ran about 15 gallons of fresh water thru the system. Closed everything up and then ran at idle for about 10 minutes while monitoring the heat exhanger, exhaust manifolds and risers with my newly purchase infrared thermometer.
Finally took it out to sea with wife driving and me monitoring temps on both engines and all four manifolds/risers/hoses. All were within 10 degrees of each other throughout the run.

The SeaFlush will come in handy for winterization. And the IR thermometer was an item my surveyor had recommended, for occasionally monitoring the exhaust system.

On a side note, I found out that my risers are stainless steel. Not sure whether that was OEM or PO.