white-grey smoke

[Guest]

Can anyone tell be what large amounts of white-grey smoke indicates, coming
from my MD2B? It reduces somewhat when the engine's warmed up.
The engine has just been repaired by a mechanic, following a blown head
gasket. This resulted from overheating, when an oil feed pipe to the rocker
mechanism came adrift. Could it be that the injectors suffered from
overheating, and need servicing?

The smoke smells like partially burnt diesel, and I've heard that poor
compression could be the cause, though the replaced barrel and rings are
very good. The mechanic had to grind the valve seats down 'quite a bit' in
order to get past the pitting and corrosion - is it possible that having the
valves seated higher could have a significant effect on compression?

After 5 months, I'm 'engined out' - as it essentially runs, I think I will
launch now for this season, smoke and all, and prepare for the next round of
work next winter. Can anyone suggest anything I can adjust (eg fuel pump
timing/quantity) to mitigate the symptoms in the meantime?

Thanks,
John B, W.Centaur 'Puffin', Puffing in Plymouth

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[chrisD]

If you have overheated the engine, you might have damaged the exhaust hose linings, as I did, which could generate a lot of steamy smoke because the cooling water cannot pass freely through the exhaust system (although this would not explain the diesel smell). The exhaust hose is relatively inexpensive, and seems to get damaged fairly easily if the engine is overheated.

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[tr7v8]

White grey smoke is unburnt diesel by the sound of it. Points towards lowish compression or maybe poor atomisation (knackered injector) or possible miss timing. A common problem if engines are overheated is a damaged pintle in the injector. I'd guess as it gets better when it warms up it could well be low compression. Volvos need special tool for removal of injectors otherwise the sleeve comes out. I'd also look for while they're out doing a compression test as maybe the overheating has damaged a bore.
How easy is it to start?

Jim
------

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[Guest]

Thanks for the reply - sounds like you really know your diesels! The barrel is a very good condition second hand replacement, so I'm wondering if the problem could be low compression due to the valve seats having been ground down so much. The mechanic did explain that he had to grind down a long way to get past the pitting and corrosion - do you think this alone could have a significant effect on compression?

BTW, I think I'll get the injectors serviced to eliminate them from the enquiry!

Cheers, John B

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[Guest]

Sorry, forgot to mention that it is reasonably easy to start, with the repaired cylinder being not quite as eager as the other one.

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[hlb]

Nearly all diesel boats smoke, especially when cold. I would not worry about it unless you have other problems like power loss or bangs and clangs!! Other than that. Go and see Gavin at MOUNT BATTON BOAT HOUSE and ask for a bottle of Soltron. Else PM me and I'll send you some. It wont mend a broken engine but it will stop the smoke, clean up the diesel of water and maybe a bit more power.

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[spannerman]

I wouldn't worry too much about the smoke as you say the engine starts readily, so that eliminates low compression as this is essential for a diesel, injectors faults are indicated by BLACK smoke as this is unburnt fuel, blue is oil as you alredy know and white can indicate head gasket problems or condensation in the exhaust. Now you have just had the heads done so there should be no problem with the gaskets, and no grinding the valves in won't make any significant difference to the compression. What I am sure you have is condensation in the exhaust, I have had several customers with older Volvo motors come in and ask about white smoke and it is mainly due to the lower temperatures at this time of the year, and you say it clears when the engine is warmed up, so there is your answer.
Regarding the cylinder which you say seems a bit more reluctant, I would have the injectors serviced as you could have one that isn't delivering enough fuel.

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[Guest]

Thanks for the helpful advice folks!

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[oldharry]

Could well be that the exhaust has diesel and oil in it following the original breakdown, and that this is now coming off. Had an old Sherpa diesel once that had its exhaust bunged up with diesel from extended attempts to start it, and initially it produced a smoke screen like something out of a WW2 Hollywood epic! After about an hours run it had cleared completely and ran just fine.

However, there could also be an injector problem if the repaired cylinder is reluctant to fire - or maybe the compression is still down causing partial ignition failure, which will also produce spectacular clouds of grey smoke.

Is the air intake clear? - blockages there can cause eitther black or white smoke, depending on whats going on. If its starting and running OK, this is unlikely.

Its not usually a good idea to grind valves down too far. Makers do specify exact limits, and your mechanic should not have ground them beyond the specs. Replacing valves is neither difficult nor particularly expensive, nor is reseating them. To go beyond specs may cause compression difficulties, and be the cause of the reluctant starting on that cylinder. It also can change the gas flow profiling which would affect combustion, and weaken the valve seating areas leading to problems later on.

Suggest you find out why he didnt simply replace the valves if they were as bad as he says, and confirm they are still within makers specs. If not then the engine is definitely not yet properly 'fixed' and could go on giving you headaches.

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[vyv_cox]

White smoke is very often steam. Try putting a cold mirror in the general area of the exhaust and see what accumulates. I've no data on this but my observations are:

Where copious amounts of water flow through either the engine or bypass to the exhaust manifold "spike", there is rarely any steam generation. Exhaust temperature is knocked right down and no steam is generated. Where the flow rate is low, or perhaps where the manifold design lends itself to this problem, steam can be generated. The classic case of this is the Bukh 10 and 20 engines, all of which seem to steam. On these engines the water pump is perhaps a little on the small side and water is injected into the engine by a crude fitting that resembles an old gas poker. This tends to block with salt crystals, restricting the flow of water, hence the steam. It is evident that the amount of water emerging from the exhaust is considerably smaller with Bukh engines than others.

Other reasons for steaming can be anything that restricts either the water flow or possibly the exhaust/water mixing. These could include corrosion of the engine block, pump not working properly for a variety of reasons, faulty thermostat, coking of the manifold and/or rubber hose. You may be able to tell if the flow rate is low, otherwise suggest you check the above.

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[maxi]

Hi john b you keep good company. My MDIIC has had a a total re-build, rings, injectors, head re-machined etc etc. Has good compression, starts well, indirect cooling so runs at 85 degrees and the damn thing still looks like a crematorium on special offer day. Blue/grey smoke, no steam.
Have had PBO's guru on the case and tried everything, to no avail. Otherwise a good engine.
The Volvo Penta users website is full of equally disgruntled MDIIC owners with the same problem - not a single word from Volvo though!!!. Green engines just ain't (environmentally) green!.

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[DepSol]

When you say you have tried everything, have you tried using Soltron?

<hr width=100% size=1>Dom

2003 is going to be a good year for me