Volvo D1-30hp smoking/ black discharge.

[Dual Control 2]

Hi, I’ve got a 2016 D1-30hp with sail drive, 1200 hours in my 10 mtr yacht. Mostly I motor around 1800rpm all good but if I increase to say 2000 or above it starts to stream / white smoke but never feels hot out the exhaust. Maximum rpm is 2600. 
The video shows me at max revs for a minute then shutting down to around 1000 rpm. Why am I getting all this black discharge? Wondering if it’s the injectors, exhaust elbow, carbon deposits??

[Island Time 1,337]

Max rpm of a D1-30 is 3200rpm. It is important to ensure that the motor can reach this rev limit under power, when everything is in good order (clean hull, prop, normal vessel loading). So, the black is carbon. White smoke is steam, and means the exhaust is too hot. Does not mean the motor is overheating (yet). So, is the hull and prop clean? When was the heat exchanger last cleaned? Exhaust elbow cleaned? This is all basic periodic maintenance. Once those things are all good, if it wont pull the 3200 RPM, prop is too large/pitch to high, or the engine is not producing specified HP...

[CarpeDiem 560]

To reword what IT said, the issue is not enough salt water getting into your exhaust pipe to cool the exhaust gasses. The exhaust gasses are boiling the salt water so steam.

The most common source of this issue is the exhaust mixer. But there's a few other things that can cause it too.

1. Remove and inspect the exhaust mixer

This is fundamentally a consumable item.  If the exhaust mixer is blocked up then it's realistically past it's use by date. They can be cleaned out but significant corrosion will have set in. I would replace it with a new stainless one. 

2. Check the lift muffler for excessive marine growth. These can really clog up with all sorts of life.

3. Clean out the heat exchanger

The easiset way to do this is reverse flushing with 'barnacle buster' but if it's been 10 years I would want to open it up and have a poke around.  And if you've ever had an impellor explode then taking the front end cap off is a must.  Beware it's plastic so don't break it. 

4. Clean out the salt Water strainer

If the problem persists after that then you could have a blocked saildrive. These can block up with marine life. It should be flushed with barnacle buster each time the boat is out of the water.   I dissolved a small colony of what I think were those cats eyes shells last time I did mine.

To prove this run the water intake temporarily to another sea cock bypassing the sail drive. 

If the problem still persists, then you probably need to think about replacing or at least inspecting/flushing the exhaust hose. 

Finally you need to be running the engine at full revs every so often. I run mine at max throttle every 50hrs or so for 30 minutes while keeping a close eye on everything. This blasts out the exhaust and helps to deglaze the cylinder bores.

 

[LBD 196]

Check the air filter is not blocked and ensure that the engine space is not too tightly sealed.

 

[Frank 192]

What Carpe Diem said !! several time I have chased causes for engine symptoms spending hours going down all sorts of  rabbit holes when all along it was the damn exhaust mixer being choked up with scale and carbon remove and clean that puppy first then  report back

[Cameron 108]

Pretty much guaranteed it's the exhaust elbow clogged up... same symptoms when it happened to me with a D1-20. Once it starts to show these symptoms it rapidly gets worse and you have to keep reducing rpm to stop the black stuff coming out the exhaust. You will probably find the elbow is so clogged your little finger won't even fit in the hole! HDI marine do a nice stainless replacement elbow for less cost than the factory one.

After replacing elbow you need to check max rpm (should be over 3k) and if you can't achieve this then change the prop.

Also running the motor a bit harder will help burn the carbon and increase the time before it blocks again.

[Psyche 879]

One way of cleaning the elbow is to get an oxy set and burn a ring of carbon around the flange at one end, as soon as its glowing red turn the acetylene off and just run the oxygen in the end. This will burn all the carbon out. The other method involves chipping it out with a thin bladed screwdriver and/or soaking it in sodium hydroxide for a few hours.  The problem with cast elbows is that the saltwater/hot exhaust gas combo corrodes the water inlet baffle so by the time they get to black smoke and reduced revs they are toast.

 

[Shackleton 3]

Aliexpress sources a cheaper stainless 304 exhaust mixer here. https://www.aliexpress.com/item/1005006734593303.html

The US  HDI marine is 316 stainless but more expensive.

[John B 117]

I agree that the elbow mixer is probably the problem..6 or 7 years is what the modern units seem to last . But no mention of an impeller check? Maybe I missed it but that is the number 1 thing to pull and change.