Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I setup my D10V plant over the last few weeks, I ran it yesterday and it took almost 40 minutes to get to steam, but the steam didn’t seem to be holding well with the engine.

The steam initially had a frothiness to it or cloudiness and there was a strange smell coming from it, almost metallic.   It’s a vertical home made boiler good for 165 psi. It only has a center exhaust flue that the flame goes up.

I can’t seem to figure it out. When I removed the water from it, it was clear… no particulates or cloudy matter.

The firebox doesn’t have water tubes, just a center exhaust flue and the flame goes up it.

Any insight would be great.

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A single vertical flue has rather limited surface area and is not very well heated as there is nothing impeding the hot gases of combustion from doing that which they most naturally do, ie: rise rapidly and exit out the chimney with only minimal brief contact with the part of the flue in contact with the boiler's water. It is usually best to have several small water tubes crossing the vertical flue to slow the heat rising and provide significant increased surface area of heating. In lieu of that, then multiple smaller flues is a good way to increase the heating surface area and is often used.

As for the "Metallic Smell" I would suggest that if it has never been heated before, that might not be unusual. It is also possible that it is assembled with certain dissimilar metals that are not quite at ionic equilibrium with each other, thus heating would instigate or accelerate any galvanic reaction that is "potentially" (pun intended) extant!?!?

If that is the case, then you may well get that smell every time you fire up, though likely less as time goes by. It is unlikely that you will note any significant deterioration in your lifetime, but depending on the metals involved, it is possible!

A single vertical flue has rather limited surface area and is not very well heated as there is nothing impeding the hot gases of combustion from doing that which they most naturally do, ie: rise rapidly and exit out the chimney with only minimal brief contact with the part of the flue in contact with the boiler's water. It is usually best to have several small water tubes crossing the vertical flue to slow the heat rising and provide significant increased surface area of heating. In lieu of that, then multiple smaller flues is a good way to increase the heating surface area and is often used.

As for the "Metallic Smell" I would suggest that if it has never been heated before, that might not be unusual. It is also possible that it is assembled with certain dissimilar metals that are not quite at ionic equilibrium with each other, thus heating would instigate or accelerate any galvanic reaction that is "potentially" (pun intended) extant!?!?

If that is the case, then you may well get that smell every time you fire up, though likely less as time goes by. It is unlikely that you will note any significant deterioration in your lifetime, but depending on the metals involved, it is possible!

My concern is that the top part of this single exhaust flue is overheated as the top portion of it isn’t in contact with water. Is there any danger to that?

If it were me I guess I wouldn't get too worried until it did the same again. It possibly could just be residue from a cleaning agent used when the boiler was made or just some kind of dirt or goop.  I'd try running it again and see if anything has changed.

Quote from: Steamburns on May 01, 2025, 11:46:25 am

Quote from: Stoker on May 01, 2025, 10:42:57 am

A single vertical flue has rather limited surface area and is not very well heated as there is nothing impeding the hot gases of combustion from doing that which they most naturally do, ie: rise rapidly and exit out the chimney with only minimal brief contact with the part of the flue in contact with the boiler's water. It is usually best to have several small water tubes crossing the vertical flue to slow the heat rising and provide significant increased surface area of heating. In lieu of that, then multiple smaller flues is a good way to increase the heating surface area and is often used.

As for the "Metallic Smell" I would suggest that if it has never been heated before, that might not be unusual. It is also possible that it is assembled with certain dissimilar metals that are not quite at ionic equilibrium with each other, thus heating would instigate or accelerate any galvanic reaction that is "potentially" (pun intended) extant!?!?

If that is the case, then you may well get that smell every time you fire up, though likely less as time goes by. It is unlikely that you will note any significant deterioration in your lifetime, but depending on the metals involved, it is possible!

My concern is that the top part of this single exhaust flue is overheated as the top portion of it isn’t in contact with water. Is there any danger to that?

Your flue is presumably copper or some alloy thereof, so transfers any heat it receives quite readily, I suspect that there is no part of your flue that is more than an inch or two above the boilers normal water level, so I don't think you have much to worry about with overheating the flue itself, unless your water level gets extremely low or you boil dry. Now your chimney has no contact with water and is only a little farther on the path of exhausting heat. If your chimney is surviving without any water to transfer its heat to, then I would suspect that your flue is doing just fine.

Thank you! That’s helpful.  I’ll try steaming it a few more times and see if I can still smell it.

It was like a very earthy copper like metallic smell or something like a stink bug and copper.    I highly doubt it but maybe there was an insect inside it.


Edit:   The chimney doesn’t have pressure associated with it. I just hope the exhaust flue isn’t thin metal, where as the chimney wall is like 1/4” thick.

How does the water taste?

I wouldn’t drink it.   Nah, this wasn’t just like a metallic smell but a very pungent and strong odor and it was alarming.

Glad you find it amusing, however!   

Haha I had to say it after the very descriptive smell 

On larger vertical boilers with tubes, the boiler is filled all the way to the top to prevent damage and as it’s heated up the water is drained down to operating level, but I’ve never had an issue on small vertical toy/model boilers.

Interesting… so I need to be filling it to like 80% or more? I am doing like 50-60%

I'm sure everybody does this a bit differently, but I usually like to start with my boilers about 3/4 full and add water whenever they get much below 1/2, certainly trying to never let them get down to 1/3 full.

But perhaps that's just me!?!?

I just don’t know what to do about this boiler. I built this entire plant spent so much time on it, and the boiler essentially doesn’t function right.   

I don’t know what the hell is wrong with it.