White Smoke (Steam?) from Exhaust

[Spirit (of Glenans)]

Well, I've been to the boat this evening and after first starting the engine and running it up to 2000 revs I ascertained that there were no visible emissions when it was cold, I concluded that it must indeed be steam. I also concluded that while the gouts of water emitted appeared to be the same volume as before, the intervals between them were greater.
I decided to start dismantling at the exhaust elbow and found that it was very encrusted, and this appears to be the main cause of the problem, as the heat exchanger matrix only had very minor deposits which I was able to remove after a soak in vinegar.
I will have to get some brick acid in the morning for the exhaust elbow however.

 

[duncan99210]

Well, I've been to the boat this evening and after first starting the engine and running it up to 2000 revs I ascertained that there were no visible emissions when it was cold, I concluded that it must indeed be steam. I also concluded that while the gouts of water emitted appeared to be the same volume as before, the intervals between them were greater.
I decided to start dismantling at the exhaust elbow and found that it was very encrusted, and this appears to be the main cause of the problem, as the heat exchanger matrix only had very minor deposits which I was able to remove after a soak in vinegar.
I will have to get some brick acid in the morning for the exhaust elbow however.

Be prepared to replace the exhaust elbow if you're going to soak it in brick acid. There's a fair chance that under the carbonate deposits there's damage to the cast metal of the elbow such that when you try to get rid of the carbonate you'll either cause a hole or discover that the deposits had been blocking a hole. Leastways, that's what happened to me. First time it needed cleaning, I got away with it, second time a series of holes was found: cue a wait of about a week for a new one to arrive from Athens....

 

[Spirit (of Glenans)]

Be prepared to replace the exhaust elbow if you're going to soak it in brick acid. There's a fair chance that under the carbonate deposits there's damage to the cast metal of the elbow such that when you try to get rid of the carbonate you'll either cause a hole or discover that the deposits had been blocking a hole. Leastways, that's what happened to me. First time it needed cleaning, I got away with it, second time a series of holes was found: cue a wait of about a week for a new one to arrive from Athens....

The elbow survived the HCL and the subsequent scraping out, with a hacksaw blade, of the space between the inner and outer skins. The inner tube has no pitting, but the top spigot, where the raw water enters, is beginning to break down and will only last one more season.
My next suspect is the thermostat; when it's heated in water my meat thermometer shows that it opens at 105.5 deg C. When I tried it with a thermometer of the type used in a professional kitchen, it appears to open at 92.5 deg C. The latter is likely to be more accurate, but is that temperature the correct one for the 'stat in a VP D1-20?

 

[VicS]

The elbow survived the HCL and the subsequent scraping out with a hacksaw blade, of the space between the inner and outer skins. The inner tube has no pitting, but the top spigot, where the raw water enters, is beginning to break down and will only last one more season.
My next suspect is the thermostat; when it's heated in water my meat thermometer shows that it opens at 105.5 deg C. When I tried it with a thermometer of the type used in a professional kitchen, it appears to open at 92.5 deg C. The latter is likely to be more accurate, but is that temperature the correct one for the 'stat in a VP D1-20?

According to the owners manual the thermostat should begin to open at 90 +/-2 C and be fully open at 102 C

I always use a laboratory thermometer !

The temperature at which it begins to open should be stamped on it. The fully open temperature may also be stamped on it

 

[Spirit (of Glenans)]

Here is the happy sequel to this story:
When the boat was lifted out I discovered that there were quite a few small mussels within the water intake passage of the saildrive. I bashed these out with a length of rebar and gave it a good blast with a pressure washer through all the ports. When the boat was re-launched, the short trip from lifting dock to berth showed no visible emissions from the exhaust, but when, on a subsequent visit I ran the engine up to temperature, the same symptoms were evident.
The output of water from the exhaust was even less than before, but the exhaust temperature below the elbow was still well below the "pain" level, and holding a hand on the elbow was bearable, up to a point. The temperature of the water coming out of the exhaust was like bathwater and my hand did not have a smoky smell afterwards. It was a humid day and I could see condensed steam on my newly painted topsides confirming the fact that it was steam I was dealing with.
Having examined all possibilities, I eventually came to the conclusion that the reduced flow coming out was a direct result of a reduced supply and the cause must lie just below the inlet seacock.
In the interest of not allowing large quantities of seawater into my engine space while clearing the problem I attached 20 inches (50cm) of spare 19mm hose to the seacock and attempted to rod the inlet with a drain-clearing spring, but this would not go in far enough, coming up against a sharp angle in the passage. I then resorted to pressurising the down the hose, by mouth, three or four times. That did the trick, obviously removing a mussel (or mussels) which I had missed earlier, and after running the engine at 2000 revs for 15 minutes nothing could be seen emerging from the exhaust outlet except pure seawater in copious quantities. Problem solved!