Too much smoke / steam

[Beakster]

Hi, my boat has an Volvo MD11C engine that seams to run fine except that it emits more smoke / steam than it should do.

The problem only occurs in forward or reverse gear, not in neutral. I'm assuming it's steam as it dissipates fairly quickly. It happens within a minute or so, and returns to normal just as quickly when back in neutral.

I've made sure the seawater inlet on the top of the sail drive flows, and it does. I've taken the drain taps out and had a poke around, they flow freely with no gunk coming out. I've also had the impeller out, that seems fine, no bits missing.

The temp gauge doesn't usually go above about 1/3 of the way, often about 1/4, so the water temperature is never apparently too high.

Water seems to exit the exhaust okay, not as much as I see on some other boats, but I'm told that some engines don't.

I'm no expert, I'd never touched an engine until 8 months ago, so I've just tried the obvious things after reading other posts.

It's just seems strange that the problem only occurs when in gear. It's the same when either under way or tied to the pontoon and not able to move.

Any ideas?

 

[sailorman]

Hi, my boat has an Volvo MD11C engine that seams to run fine except that it emits more smoke / steam than it should do.

The problem only occurs in forward or reverse gear, not in neutral. I'm assuming it's steam as it dissipates fairly quickly. It happens within a minute or so, and returns to normal just as quickly when back in neutral.

I've made sure the seawater inlet on the top of the sail drive flows, and it does. I've taken the drain taps out and had a poke around, they flow freely with no gunk coming out. I've also had the impeller out, that seems fine, no bits missing.

The temp gauge doesn't usually go above about 1/3 of the way, often about 1/4, so the water temperature is never apparently too high.

Water seems to exit the exhaust okay, not as much as I see on some other boats, but I'm told that some engines don't.

I'm no expert, I'd never touched an engine until 8 months ago, so I've just tried the obvious things after reading other posts.

It's just seems strange that the problem only occurs when in gear. It's the same when either under way or tied to the pontoon and not able to move.

Any ideas?

it could be just the thermostat open & closing.
when under way the engine is working harder than in neutral

 

[KellysEye]

You mentioned smoke/steam but go on to mention only steam. We have an MD17C and in cold weather some of the hot exhaust water turns into what look like fog, or at night like white smoke. On the smoke front you should expect some smoke because MD's were built before emission regulations came in. None of that happens in neutral, only when load is applied.

 

[Beakster]

Thanks for the replies so far. I should also mention that this has only started to happen in the last 10-15 hours of use if that helps.

 

[lw395]

It could be that the mixing elbow is gunked up, so that the cooling water is not mixing with the exhaust properly.
Water flow could be down. Maybe check impeller and sea water circuit?
Your water lock or silencer may have become damaged or tilted over so that the exhaust gas is not mixing with the water as it should.
If you put your hand in the exhaust, is the steam very hot and the water quite cool? (please don't scald yourself!)
Is the engine running hot for some reason?

 

[ianj99]

Check the water inlet strainer and the pump impeller. If the water flow is restricted what there is will get hotter and more of it will turn to steam.

(If it was exhaust & not steam it would reek)

It only happens in gear because with no load, the exhaust temperature is much lower - too low to turn the exhaust cooling water to steam.

 

[Beakster]

Just having a bit more of a play and I would say I'm 99% certain it's steam as when I return to neutral at low revs after being in gear at higher revs it takes a while for the emissions to die down, surely if it was smoke this would stop being emitted immediately - I think.

I might have a look at the thermostat as it's the next easiest this to look at, I suppose it could be a bit gunked up??

 

[sailorman]

Just having a bit more of a play and I would say I'm 99% certain it's steam as when I return to neutral at low revs after being in gear at higher revs it takes a while for the emissions to die down, surely if it was smoke this would stop being emitted immediately - I think.

I might have a look at the thermostat as it's the next easiest this to look at, I suppose it could be a bit gunked up??

on one of our engines one could look astern & see when the thermostat was opening

 

[VicS]

Assuming this is a directly cooled one .

Check the cooling system right through from inlet, the strainer, the condition of the pump and impeller. ( Change the impeller, dont put the old one back !)

Check the bypass in the thermostat cover. While you are doing that you might as well remove the thermostat and check that it just starts to open at the specified temperature, which should be marked on it. but if its not showing signs of overheating on the gauge the thermostat is not likely to be defective.


Check all the hoses for signs of internal collapse . Check that the water injection into the exhaust is properly clear.