Steam in Exhaust

[Scallywag]

Hello Forumites,

I have a large amount of what I believe to be steam coming out of my exhaust. I have a Volvo Penta D2-40 engine on which the raw water is sucked through the saildrive, through a raw water filter, to the water pump on the engine, to a Vetus anti-syphon valve, then into the heat exchanger on the engine and from that into the exhaust elbow.

When the engine is at idle speed all appears OK. When in gear and under load, stream appears in the exhaust. Water comes out of the exhaust but the exhaust sound is more "tractor-like" than usual when under load.

Since the problem arose I have chemically cleaned the heat exchanger, replaced the valve in the anti-syphon valve, checked the impeller and all the connections.

I have now watched closely the water system when the engine is under load in gear. I can see air appearing from time to time in the anti-syphon loop.

1. Am I correct that there should be no air in the system at all when the engine is running?

2. Does anyone know how warm the exhaust elbow should feel? (at idle it is cold and under load it is hot but not so hot it cannot be held).

3. Is it OK to bypass the anti-syphon device (i.e. connect the water pump outlet straight into the heat exchanger) or will this cause water to be sucked back into the engine? I would only does this as a test in the marina when there is no risk the exhaust outlet can be below the water to eliminate the anti-syphon device as the problem.

4. Any other things to check/ideas?

 

[RichardS]

How warm is the water actually coming out of the exhaust? If that is as cool, at least as cool as it always was, even at high revs and there is a good volume coming through, then I can't see that the steam can be being generated in the exhaust elbow. If the discharge is hot or lacking in volume then it does sound like a problem in the seawater side.

If the coolant level is not going down then it can't be coolant being vapourised in the cylinders.

Richard

 

[Billjratt]

Is the volume of water still the same? Does the "steam" smell of paraffin(ish), is the power down?.
If you have these symptoms one of the atomisers has blown a tip.

 

[Yngmar]

It certainly all sounds like yours isn't moving enough water through the heat exchanger. "Tractor sound" from the exhaust means it's no longer water muffled, likely due to what little water is making it through flashing to steam.

My MD22 was also emitting steam (but still some liquid water) at high RPM when I'd just bought the boat. It turned out to be fouling that had grown inside the saildrive leg (there are water channels leading up from the intake holes at the bottom to the seacock fitting at the top.). Entire fully grown mussels were living in there! This was most likely due to a prolonged period of disuse while the boat was for sale.

I only noticed this when I hauled the saildrive and gearbox out of the boat and split them to renew the big rubber ring connecting them to the hull. Even split it wasn't easy to dislodge the mussels, I ended up shoving a bamboo stick down there to smush them while flushing from alternating sides with a hose. Doing this with the boat in the water would be impossible. On the hard you could take the seacock out of the saildrive and poke around in there, but that would only let you reach one of the two channels in the leg. Acid might work, but is not recommended as it would also eat at the aluminium alloy of the leg.

In the water, all you can do is try and backflush the leg from the inside. Take off the hose nearest to it, above the waterline, stick the marina hose in there, open the seacock and turn the hose on. The water may dislodge things in the leg and push them out the bottom intake holes.

Another thing to check is the heat exchanger end fitting where the raw water first enters it. That's often where missing impeller pump rubber blades end up and block the small tubes in there. This only makes sense if you don't know the history of the boat, or you did find missing blades upon replacing the impeller.

The exhaust elbow on my MD22 is never too hot to touch.

 

[Tranona]

Sounds like there is not enough raw water getting through. in addition to yngmar's suggestion that flow may be reduced because of blockages in the intake, you also need to check the raw water pump and impeller and all the hoses, particularly the connections as it sounds like air is getting in. Doubt the antisyphon is the problem although good idea to clean it. The other common problem is the lid of the strainer not making a good seal, or having a crack in it.

The hot exhaust elbow is a sure sign there is insufficient flow of raw water as it is cooled by injecting the raw water in.

Best to fix it before running the engine for any period of time.

 

[Venus1]

I've had similar problems - solved by blocking off the sail drive water intake (which kept fouling with mussels) and installing a separate sea cock. Another hole in the hull, yes - but it did the trick. No more clogged intake, reduced raw water flow, and raspy exhaust note

 

[Halo]

If you are close to a fresh water mooring (e.g. canal entrance) then a week or two in there will kill any live sea bourne fouling and may aid the flushing described earlier by others

 

[Yngmar]

On my anti-syphon loop, the valve is at the top and easily covered with a wad of blu-tack or a hand for a quick test to ensure it is free of blame.

 

[Scallywag]

Thanks to all those who replied to my post.

I have only now been able to return to my boat. With your help I have identified and solved the problem. I removed the hose from the seacock (on the saildrive) to the strainer and connected a hose and back-flushed. That did the trick - now, when the engine is run, the water flow is much better, there is no air in the hoses and the steam has stopped. As a number of you suggested - it must have been growth / something in the saildrive leg. If it occurs repeatedly I will install a separate seacock for the raw water, again as suggested.

I should have tried this earlier but what was throwing me was the air in the system - the flow must have been so much constrained that air was being drawn in through what would normally been sound joints.

Again, all, thanks for your help.

 

[sarabande]

perhaps worth investigating the "air was being drawn in through what would normally been sound joints" idea. I don't go with sound joints leaking under abnormal suction or pressure, as they might be a point of failure under normal use. The source of air needs identifying - could it even have been inducted from the anti-syphon ?

 

[Norman_E]

I had steam in the exhaust and less water flow than normal when I moved the boat in January. At first I thought I was seeing "steam", (actually water vapour) because it was cold, but on investigation I found that the rubber sealing ring in the raw water filter was missing, allowing air to be sucked in instead of water. Some water was still coming through. but less than normal, leading to a hotter than normal exhaust with some of the water boiling. Check for air leaks in the raw water system upstream of the water pump..