bellows on exhaust pipe melting

[clonefever]

have 02 larson with 3.0 volvo replaced bellows hose(8 inch) last year. put new one on last year,now whole engine compartment smokes, hose clamp cut the the bellows and appears to be charred. bought boat used last year, what is the cure, new bellows same result again. engine runs at 180 degrees so don't know why its charred unless mechanic got it hot changing oil, with water hose, he had to suck oil out from top as oil plug was rusted/ rounded off. very frustrated

 

[Maclin]

Re: bellows on exhaust pipe melting

The raw cooling water is expelled into the exhaust and mixed with the exhaust gases in the riser. This cools the exhaust and keeps the rubber parts from overheating. It does not take long to cook the rubber with raw exhaust and no cooling so it could have happened any time the engine was run long enough with no raw water supply. The rubber will usually cook before any real engine damage occurs. I do not have an explanation for why it is smoking now if the engine can stay at 180 and not overheat. If the raw water is not mixed with the exaust and is not exiting anywhere then the temp will climb way past 180 and the engine will overheat.

Is your exhaust stock, no thru hull or other mods?

 

[hezzy602]

Re: bellows on exhaust pipe melting

Do you have water shooting from where the exhaust leaves the boat. If you dont, maybe your thermo is giving you a bad reading? Like Maclin said the water cools your exhuast. Either way check your thermo because if its is and your running this thing while its overheating thats not going be good.

 

[seattle2855]

Re: bellows on exhaust pipe melting

have 02 larson with 3.0 volvo replaced bellows hose(8 inch) last year. put new one on last year,now whole engine compartment smokes, hose clamp cut the the bellows and appears to be charred. bought boat used last year, what is the cure, new bellows same result again. engine runs at 180 degrees so don't know why its charred unless mechanic got it hot changing oil, with water hose, he had to suck oil out from top as oil plug was rusted/ rounded off. very frustrated

I was dealing with the same problem earlier this year. Essentially you're not getting enough raw water circulating through the system. You have enough to keep the engine at the right temp, but not the exhaust.

You either:

1. Have a bad impeller pump/housing.

2. Blocked manifolds or risers -- they only last so long.

3. Blockage somewhere in the raw water system (like a broken impeller blade).

You can disconnect the raw water supply as it comes into the engine compartment and run the motor for a few seconds. You should have a strong water flow. Also you can remove the riser and check the ports for rust scales.