Volvo MD2030 black smoke and lacking power

[MM5AHO]

OUr boat has a 20 year old MD2030.
First outing for the year yesterday, and I noticed that at the rarely used higher revs it blows a little black smoke and lacks power.
At or under 2000rpm it seems to run fine, and does the usual 6 knots. (Its a Rival 32, they're not fast).
Starts fine, idles smoothly, no unusual vibrations, does everything normal up to 2000 rpm. I rarely run it faster that this speed ad fuel consumption becomes markedly worse for little gain in speed. But I did try to push it up a bit yesterday afternoon into a headwind, and noticed these new symptoms.

Thinking that it's got to be either fuel or air, I changed the fuel filter. This seemed unlikely, as I'd changed it over the winter, and also "vacuumed" the stainless fuel tank to clean any gunge sludge etc, as I do every winter. There was a little, water, black stiff and general dirt. All out, clean diesel.
The filter I removed looked clean, but I put a new cartridge in anyway.
No change.

So... air? Removed the air inlet manifold. This is a small cast aluminium box section with a grill in one end, through which comustion air passes into the inlet manifiold. No blockage, nothing wrong there.
Actually it runs fine at 2000 rpm, and we proceeded to motor for another 12 miles without any obvious issue.

So symptoms are:
On increasing throttle, to get more power, past 2000 rpm, the exhaust blows a little black smoke. Not clouds, just some. Te engine doesn't rev as high as it should (should do about 3000 tops), and there's no increased power over that developed at 2000rpm. Not overheating, no vibration, no other obvious symptoms.

Any suggestions?

 

[Adjag]

Hi
Given the checks you've already done it sounds very like the exhaust elbow is blocked to me, this is the pipe where sea water is injected into the exhaust gases before passing into the silencer. It gradually fills with Carbon and the blockage reduces the engine's airflow which can cause reduced power & black smoke just as you have. I removed mine as a precaution on our 15yr old MD2020 and had lot of fun soaking it in Cementone brick cleaner to clean it.

Hope this helps - there's lots of advice on how to remove it if you google the subject

Thanks adrian

 

[MM5AHO]

Thanks Adrian, that sounds like a good place to look.

 

[duncan99210]

I agree that the symptoms are a blocked exhaust elbow. Remove it and clean it but be careful as you clean it. There may be corrosion which has weakened it and poking about with a screwdriver or similar may just lead to a hole in the elbow, requiring an (expensive) new elbow.

 

[tillergirl]

That's how it was with me when my 2030 exhaust elbow was blocked.

 

[Tranona]

You can perhaps reduce the chances of it happening again by running the engine harder and possibly longer at a time. They do not like long periods of light load running and that is what causes coking up of the exhaust. They like running at about 2400 for cruising speed and propped to achieve hull speed at just under maximum revs, around 3400.

My similar 2030 has done 3500 hours mostly at 2400 and the exhaust has never been touched.

 

[theoldsalt]

MM5HHO,

You may well have a partly blocked cooling water exhaust injection port due to extended use at low revs and light load but I think that would likely cause overheating due to poor cooling.

There is another possible cause.

Have you ever run the engine at full revs for any significant time before? If not then maybe the symptoms has always been there without you realising it. If so then maybe the engine is over-propped. This can give good low revs power and fuel economy but the extra load prevents the engine reaching the demanded revs and therefore prevents efficient burning of the fuel at higher throttle settings. This results in black smoke.

 

[MM5AHO]

Old salt,

Yes most years I do run at high revs, not usually extended, but to give it a "blow out" (even if it doesn't really, more to know that it runs).
It runs up to about 3500 rpm, digs the stern down into the sea, makes an enormous wake, and goes between 0.5 and 1.0knots faster.
What it does do though is normally generate enough power to deal with adverse wind. tide or whatever.

So this current performance is abnormal.
Good thought though.

 

[theoldsalt]

MM5AHO,

I suggested a possible alternative cause as in the past I have had two engines with partially blocked exhausts due to carbon build-up (by previous owners) neither of which caused revs limitation.

Well good to hear at least that's one possibility excluded. So back to the possibility that the exhaust may be partially blocked. I hope you get it sorted soon.
Good luck.

 

[J Neeves]

I'd agree blocked exhaust outlet. Its not carbon by the way but calcium carbonate discoloured by carbon. It can be removed by soaking in acid but if you have any corrosion, quite common, then you have chance of simply dissolving the whole thing away. We have found we can do one acid clean only, the second time you need a new part (and as someone said, expensive). I have been told stainless replacements might be a better option, for some reason less chance of formation of calcium carbonate. You might also find a stainless one is cheaper than the standard Volvo part (which is a pretty simple casting).

We find that the elbows block (or block to the point where they impact performance) at about 1,000 hours. But it might depend on the levels of dissolved calcium in the local seawater.

Its an easy check though you need more antifreeze as it empties all over your feet as you take the heat exchanger apart. You can flush out the heat exchanger at the same time as its going to be removed anyway. As soon as you take the elbow off look at the 'engine end' - if its blocked it will be obvious. I'd say the most difficult thing to do is getting the rubber hose off the elbow.

Jonathan

 

[Allergy]

Hi
Given the checks you've already done it sounds very like the exhaust elbow is blocked to me, this is the pipe where sea water is injected into the exhaust gases before passing into the silencer. It gradually fills with Carbon and the blockage reduces the engine's airflow which can cause reduced power & black smoke just as you have. I removed mine as a precaution on our 15yr old MD2020 and had lot of fun soaking it in Cementone brick cleaner to clean it.

Hope this helps - there's lots of advice on how to remove it if you google the subject

Thanks adrian

+1

 

[MM5AHO]

The collective opinion is right. The exhaust elbow was blocked. The hole remaining was less than the size of a pencil, perhaps 5mm x 5mm.

I start a new thread with some tips for changing these.

 

[Mrnotming]

Oops! Just taken off mine on a MD2030.2000 vintage.Did not survive the treatment.I managed to poke a hole in it(almost) so perhaps a good idea to dump.After all it will be the first thing to have had to replace other than normal filters and oil.Hopefully Volvo prices here will be euro based!
P.s. Got it off without spilling any coolant.Unscrewed jubilee clip clamp until it fell apart,leaving enough room to wiggle back the elbow.So handy replacement I hope.

 

[sailaboutvic]

I had a S/S elbow make this year , a lot better option and cheaper , volvo elbow are known to get blocked , as a rule I use to remove mine each year and give it a clean , I hoping I won't have to do that now .

 

[Birdseye]

OUr boat has a 20 year old MD2030.
First outing for the year yesterday, and I noticed that at the rarely used higher revs it blows a little black smoke and lacks power.
At or under 2000rpm it seems to run fine, and does the usual 6 knots. (Its a Rival 32, they're not fast).

Sounds good to me. My boat is a starlight 35 with the same engine as yours and it staggers to 6kn in a flat calm at 2600rpm! And thats with a clean hull - with a bit of weed it did 5.4kn

 

[Mrnotming]

Oops! Just taken off mine on a MD2030.2000 vintage.Did not survive the treatment.I managed to poke a hole in it(almost) so perhaps a good idea to dump.After all it will be the first thing to have had to replace other than normal filters and oil.Hopefully Volvo prices here will be euro based!
P.s. Got it off without spilling any coolant.Unscrewed jubilee clip clamp until it fell apart,leaving enough room to wiggle back the elbow.So handy replacement I hope.

Just to say that a new part should arrive Friday, quoted €287 ish Hors tax.So it looks like buying in France will avoid the sterling inflation.9Accastillage Diffusion,Martigues.