Inboard Diesel Exhaust

[Shaun]

Gday,
Ive tracked down a problem of water not getting out, on my inboard diesel to a blockage in the exhaust manifold(if thats whats its called?), the water is pumping well now through the engine & into the little inlet pipe at the top of the pictured exhaust pipe but its blocked... so its not getting out and mixing with the exhaust gas & then into the water lock.
I presume the raw water cools the inside exhaust pipe in a jacket type process.

exhaust.jpg (125.22 KiB) Viewed 4646 times

I suspect the steel exhaust is blocked with either salt or rust, exhaust fumes get through ok, but not the raw water.
Ive water blasted inside the pipe, but still blocked.
Im about to try my old friend Hydrochloric Acid, to see if that unblocks it...any other ideas?

cheers
shaun

[Miker]

Something a little more subtle, like Drano?

The other thing you could do is cut it in half and have a look inside, then weld it up again.

Michael

[Dolphin]

G'Day Shaun,
A blockage in the "Mixing Elbow" is a common problem. You can drill it out if there is enough metal there.

It maybe that it is just salted up. The salt crystalises at 85deg C into a hard salt that, believe it or not, doesn't disolve in water. To get rid of these salt deposits mix up 1:1 water and vinegar. Soak the parts for about 24 hours if you can and preferably in a hot solution. I have found that if your water is blocked then the enging has been running hot and is probably salted up too. To confirm this you can usually remove the thermostat and see what sort of salt encrustation you have on the thermostat. (If its raw water cooled).
Forthe rusted parts try and chip all the rust off. You can then try a rust converter with a base of phosphoric acid. Don;t use the car ones they're a bit light on. Bunnings have a good rust converter, I'll try and find the name of it. It produces a hard black finish. You may find there is not enough metal left to do anything with and you may have to fork out for a new mixing elbow. (ouch) They usually only last 5 years if you get a good one. The Hatz (BMW Marine) elbow was $874.95 They rust out quiclky because the exhaust has sulphur in it that makes sulphurous acid and hot salt water is very corrosive. These things just sit in the exhaust pipe while you're away at work!
If its not in the manual, the cooling water should flow at about 20 litres per minute at 2000 engine rpm for a Hatz diesel. That doesn't matter if the engine is hot or cold or loaded or not. The cooling pump determines how much water is used. If the thermostat is shut, ie a cold engine, the water is bypassed to the exhaust pipe to "put the fire out" and to muffle the exhaust noise. Simply put a bucket under the exhaust pipe outside the boat and let it run OR fill a bucket in the cockpit and connect a hose to the cooling water pump. Of course a 9 litre bucket will empty in under 30 seconds. Be sure to check ALL the cooling system from go to whoa. Although you said the water flow is good up to the mixing elbow. I even had a salt blockage in the inlet to the engine at the brass fitting. I made a rubber gasket to replace the exhaust mixing elbow gasket and that allowed me to fill the engine with water/vinegar solution to pickle it out.
I hope that helps.
How is the access to the engine?
Greg.

[Dolphin]

Here is a photo of Felicite's mixing elbow. It was a write off eventually.
Greg.

[Miker]

Shaun, you might want to look at this company. http://ppcco.com.au/

I don't have any affiliation, but have used their paints on various parts of my Harley and they're #1 in my book. It's not cheap, but I'm sure you'll get a good result. They're most helpful too, so if you email them with your problem, they'll most likely give you a pointer or three.

Cheers,
Michael

[bearmcnally]

Hi Shaun


Ive just had my BMW D7 re-built spent about $3000 on it Manifold $1200 now its stainless along with bits and pieces looks like new.Had a jacketed exhaust like yours but it corroded replaced it with a Nanni waterlock and rubber hose works like a treat.If you still like your wet exhaust and it can't be repaired Porter Props makes them.


Regards Bear

[Shaun]

Thanks for the replies fellas,
The vinegar treatment didnt work, so cut it in half, no wonder the vinegar didnt work, its a right off, extremely corroded inside the jacket, virtually jamb packed with rust flakes.
I'll have a bash at fabricating an identical one, should only take half a day and $15 worth of pipe

cheers
Shaun

[Dolphin]

G'Day Shaun,
the vinegar/water solution only works on salt crystalisation"
Phosphoric acid works on rust but it converts it to Iron Phosphate a hard form of iron (I think).
Looking at that mixing elbow it seems that you could make one easily. I guess that it would have two pipes one inside the other for a short length.

I'd be keen to see what the result is.

The Hatz manifold in the picture seems to have a section that cools the pipe before dumping the cooling water into the exhaust pipe and putting the fire out before it gets to the rubber exhaust hose.
The Volvo mixing elbow has a similar arrangement where it has two pipes, one inside the other. Theyre quite large diameter, from memory about 50mm or more.

Could I be so bold as to suggest as you are making a new mixing elbow, that at the same time you make a spare. That way when it blocks up again, in 5 years time, you can quickly swap it over and take your time to make another one.
I hope that helps.
Greg

Volvo mixing elbow sketch

Volvo mixing elbow.JPG (9.01 KiB) Viewed 4592 times

[Shaun]

Thanks again for the replies, ive learnt alot from them.
I considered changing the design, by making the space in which the raw water circulates the exhaust larger, after seeing the Gregs sketch, maybe making the outside diameter 65mm instead of 50mm, but they only had 50mm 90deg bends at the metal supplier, so went with the same as original(only made one, will knock another one up when needed, re-used the neck/piece that bolts onto the side of the engine)

The 90deg pipe bends come in two variety, a shorter one & an elongated one, fortuneatly or by design(?) the 35mm elongated fits perfectly inside the 50mm shorter one. I also reused the small stainless steel raw water inlet pipe, keeping with my DIY philosophy I tried to weld this small pipe onto the steel 90deg bend, but kept blowing holes in it, it ended up half the original length, before I took it to the welders to have them do it, also got them to weld the last small reduced diameter section, that goes onto a hose, then feeds into the water lock, as i was having trouble welding the Duragal pipe thats harder to weld than standard steel


The result
Pipe(offcuts) & x2 90deg bends $10
welding $35
about $3 of welding rods

jacket design

mixingelbowjacket.jpg (80.15 KiB) Viewed 4563 times

Now I just have to hope I got the correct downsloping angle cheers
Shaun

[Dolphin]

G'Day Shaun,
YOu've done a good job. Maybe you better start knocking them out.

Btw, did you know that gal pipe is hard to weld because the zinc fumes short out the arc. If you grind the gal off before welding it, it wont happen and you'll get a better weld. The fumes from the gal are not good for you and you should avoid breathing them in. Welders get a kind of flu like symptoms if they get too much fumes in them. It partucularly happens on mondays when they are not used to breathing in the metal fumes over the weekend. (Strange but true).

If you are having trouble welding the small pipe to a heavy gauge one, you can run a weld on the pipe only at low current to build it up and then weld the two pieces together. By the way, I'm prety good at fixing blow holes, plenty of experience!

Good job, hope it runs well.

Greg.