Copper Wet Exhaust Soot Cleaning?

[Oatman]

As part of my Winter refit, I removed the Wet Exhaust for inspection. It is made (according to the survey) of copper tubing, approx. 2 1/2" OD.

It came out in 2 pieces. The first piece consists of: 1. a nipple connecting the manifold mounting flange to the water elbow; 2. The water Elbow, which descends at 45Degrees and has an 1 1/2" nipple for the water injection; 3. A 90 degree elbow to Strb and a 28" run to the outboard bottom of the cockpit locker; 4. Another elbow, with a 30" run to the top of the locker; and 4. A an elbow turning aft with a 12" run to a threaded union. The second piece is: 1. A threaded union that connects to the first piece and a 24" run to; 2.the muffler, which has a nipple on its aft end for a flexible hose to the thru hull.

There are 2 other 1 1/2" nipples, one on each side of the union, which leads me to believe there is an interior water jacket and water doesn't mix with the gasses until they all reach the muffler.

My problem is that all the bends and tubing are welded together, which prevents me from cleaning the accumulated soot inside or inspecting the water jacket. Looking through the ends of each piece with a flashlight, I notice a considerable accumulation of soot.

Does anyone know of a solution I could pour into these two pieces that would dissolve the soot, without damaging the copper? What about corrosion in the water jacket?

Any response would be welcome. Time is getting short! Thanks

Oatman

[delmarrey]

Unless the soot is coming out in chunks restricting flow or building up in the exhaust elbow, why would you want to clean it out?

Then there is your local chimney sweep.

[Oatman]

Well, I never noticed any "chunks" but there's quite a bit of black deposited on the transom, where the exhaust exits. Also, visual inspection of the elbow before the bend shows deposits on the walls, although I'm not sure how thick it is or when it becomes a problem. Perhaps I'm trying preventive maintenance.

[delmarrey]

It sounds like you may be overloading the motor or you have an injector problem. Too much un-burned fuel going thru the system.

[Oatman]

I agree, delmarrey; its a 13HP Volvo Penta, turning a 1" shaft and a 13" prop, to drive a 14,000 lb. boat. My research says the correct HP should be 24-35 HP. I would love to repower but am not able to do so at this time.

I'm planning to cruise thru The Great Lakes next Summer to The Atlantic and think it should be sufficient for this (no tidal flows or current to fight). I am,therefore, reluctant to invest in tinkering with the injection. But that's another post.

My concern here is what I've read about Exhaust Back Pressure caused by soot build up. Do you think this is not a legitimate concern? Should I simply reinstall the exhaust?

[delmarrey]

2-1/2" seems adequate enough for a motor of that size but w/o knowing what model & year motor you have it's hard to say for sure.

Usually the exhaust elbow would be the heaviest build up due to the heat cooking the stuff on. If that's clear then the rest should have enough volume for the system to breathe.

And 13 hp is really on the light side. The recommended ratio is 1-1/2 to 2 hp per 1000# of vessel.

One test to to check the prop is to give it full throttle from a dead stop in the water. If the motor dogs down then you have too much pitch to the prop. Are you able to make hull speed?

Back pressure can be measured by drilling a hole the exhaust pipe between the wet lift and taping for a 15 lb pressure gauge. If it's rubber then just a hole small enough for the gauge to screw in, it'll make it's own threads.

At an idle the pressure should be around 1.5 to 2.75 psi, at least that's what the trucks ran at in our shop but your motor may be different. I'd check with the factory spec's first.

[ConradG]

Unless there is buildup, I wouldn't worry too much about soot in the exhaust. Most diesels don't burn all that clean! Add a little oil from blowby and it can get kinda thick and chunky in there. I've used the torch and compressed air to burn out carbon buildup but I wouldn't linger too long with copper! Sometimes it's better not to fix what ain't broke!