Oil from exhaust?

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jake44

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Engine: Volvo Penta 10HP
On revs 3/4 and above I am getting black colouration in exhaust water (bad enough to cause noticable slick).
My engine knowledge is limited and I would appreciate advice in this matter.

Thanks in advance -
Jack
 
Is it a black sooty type film on the surface which goes when you reduce the revs or the boat picks up speed - this is normal if you put the engine under sudden load or are slightly over propped and is usually a result of unburnt fuel.

Or is it actually oil - which probably indicates a more serious problem
 
L'escargot -
It certainly reduces when revs reduce but I would describe it more like oil (water is blackened as exiting exhaust)

jake
 
I would say that the fact that it reduces with the revs suggests that it is more likely to be overloading. Most small diesels will throw out sooty/oily exhaust water under load and other factors such as something around the prop or a dirty bottom can bring it on as well. They also get more prone to it with age and wear. Clean injectors or pump adjusting can sometimes help.

If it was my engine and it ran alright otherwise at normal revs and there were no other indications of anything wrong, I wouldn't be too concerned. (But I have been desensitised by having a 25 year old Yanmar which runs on regardless). Monitor it and if you are still concerned a quick once over by a mechanic may put your mind at rest
 
Jack; As the hull or prop becomes increasingly fouled you
attempt to get to your usual cruising speed by throttling up. Your engine whatever prop set up you are using has already reached its maximum achieveable revs,and by adding more diesel which the cylinder cannot burn, ejects it in the exhaust leaving a dull black trail in your wake.
I had this problem with my Yanmar,but after fitting a rev counter, found the engine was revving fine but I was trying to push it faster than my 13x 8 prop wanted to go.
 
Often caused by sumpgasket leaking air into system, if the gaskets go they can suck in as well as spew out. this can over inrich the fuel casing a lose of engine oil or more likely......fuel.

would be a good idea to get it to a marine engine expert.

i hate that word ....expert.......ex meaning dead and spert meaning a drip under presure
 
<Often caused by sumpgasket leaking air into system, if the gaskets go they can suck in as well as spew out. this can over inrich the fuel casing a lose of engine oil or more likely......fuel.>

the sump gasket sits between the sump and the engine block, if the gasket leaks all that happens is that you get oil dripping out. quite how you get the idea that the sump has something to do with fuel system i dont know. it is a container to hold the engine oil that is all.
 
thanks for the mechanical wizardry sonsy, loss of presure in the sump can lead to over presure in the valves, this can lead to oil being pulled into the system. if the presure in the sump drops on acar engine this can lead to over worked pistons. presure in asystem is only present when all air ways are closed. perhaps an ice cream tub would be better to hold the engine oil rather than a sealed unit. if the presure in the engine oil drops, the valves can work overtime. if this hapens then the resulting loss of fuel from the pisten can result in loss from exhaust. basic physics of combustion. have a good day all.
 
My MD5a 25 years young suffers the same fate if I ask it to do too much......Dont worry, its unburnt fuel etc that the engine is unable to cope with........provided she starts ok i.e no lack of compression and she does not burn too miuch oil I would not worry about it, just dont give it too much welly, max throtle revs that no dirt is seen in the exhaust will do the trick.

Paul.
 
Sorry Bob - quite mystified by this. There should be NO pressure in the sump - it is vented via the breather either externally or into the intake manifold which operates well below atmospheric pressure (including a turbo where it vents into the external air intake). The valves have nothing to do with it - they open and close to allow the fuel air mix in to the cylinder, and allow the exhaust gases to escape, and are completely unaffected by what is happening in the sump - a different part of the engine. The valves cannot 'work overtime' unless the engine is over -revved, as their operation is governed entirely by the rotation of the engine. Either they work or they do not. If not the engine will be very dead and usually very broken!

Going back to crankcase pressure there is a well known symptom in a worn engine, whereby worn piston rings allow combustion pressure to escape into the crankcase. If the breathers are blocked or the blowby is excessive, then pressure increases in the crankcase, and lubricating oil spray is forced out through the breather. If the breather is connected to the inlet manifold as is commonly the case with diesels then the oil is drawn back in to the combustion chamber and most of it burns off. Some survives and is blown out of the exhaust, which will be emitting a huge amount of blue smoke: far more than the blue haze from a worn engine. A badly worn engine being worked hard can accumulate sufficient oil in the inlet manifold to run on for a short while - clattering and banging and producing huge amounts of smoke - until it has cleared the manifold. Dead scarey the first time you see it happen, because the brute appears unstoppable and is making the most unparliamentary noises!

From Jacks description this does not appear to be happening to his engine though, and I am inclined to think it is unburnt fuel going through either due to engine wear, or injector problems.
 
Certainly on my old Yanmar the sump is totally unpressurised - the only thing that stops the oil running out of the breather is that it has a tube on it to bring it up above the oil level. I have also experienced the blow by oldharry refers to and had the engine run on lube oil - you know without a doubt that there is something wrong! I certainly don't think that this is what jake is describing here.

I think the general consensus is that as long as his engine is not consuming significant amounts of oil and is running ok in other respects, he doesn't seem to have too much to worry about.
 
Had exactly this symptom with a raw water cooled yanmar. the problem was glazed bores allowing excess oil into the cylinders, part of which burned but most of which came out with the exhaust as an oil slick.

But dont make the mistake I usually do of assuming the most expensive and complicated cause for a problem. Most boat engines seem to leave a little bit of oil on the water (I spent a lot of time looking at other exhausts when I had my problem!) and they still function OK. So unless you are an ecofreek, might be best just to keep an eye on it.

There are other possible causes anyway, like duff valve seals allowing lube oil to get into the cylinders. But whatever the cause, lube oil in the cylinders sounds like the source of your problem - being heavy it only partly burns during combustion, and its a problem that does get more obvious with a good flow of water through the exhaust and a decent throttle opening
 
Have you considered that your Exhaust Water Injection Elbow may be blocked with carbon and gunge? - particular if you are raw water cooled. Common after many years use. I have had it twice on both mine and a friends engine. Easy and relatively cheap to rectify by either a new elbow or cleaning, BUT to view it properly you MUST remove it and examine carefully. You won't see anything by removing the hose and looking up it.
I would look at this elbow before considering retiming, new injectors etc. After replacing the difference in performance was amazing!
 
[ QUOTE ]
Engine: Volvo Penta 10HP
On revs 3/4 and above I am getting black colouration in exhaust water (bad enough to cause noticable slick).
My engine knowledge is limited and I would appreciate advice in this matter.

Thanks in advance -
Jack

[/ QUOTE ]Further to the posts above, black smoke from your exhaust or black cooling water is symtomatic of carbon which usually comes from incomplete combustion of the fuel (too rich). In a diesel it is not so much the volume of fuel as the spray pattern from the injector(s). Engine temperature also plays a role - if the engine is cold or more precisely the piston crown, then black smoke can result. Unl;ess you are prepared to spend a few (many) beer tokens then I would leave well enough alone and avoid thrashing the engine. Lube oil in the pot can come up the bore if the oil control rings are worn or if the bore is glazed or damaged or it can come from the vlave stems if the valve stem oil seals are leaking. If the sump breather is blocked teh sump can become presurised and force oil past the oil control rings as well as past the crankshaft oil seals (oil in the bilges). Sumps are normally open to the atmosphere to prevent any buildup of pressure. This is achieved via a breather either to atmosphere of connected to the inlet manifold. Unless you can DIY the repairs it probably will not be economic to do much to the engine and the question arises "where do I stop?" head off, regrind valves, new seals, new head gasket, new rocker gasket, have injector and pump overhauled, remove piston and crank, deglaze bore (or reline) new rings, new bearings, new sump gasket, overhaul or replace lube oil pump, new crank thrusts.............. oops - cheaper to buy new engine! but this time not a volvo /forums/images/graemlins/wink.gif

All in all leave well enough alone and monitor lube oil consumption....
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You say black discoloration...What engine????? How old......what else has changed recently.

This is symptomatic of overload...Such things as replacing the propeller with the wrong one or even just a dirty hull or weedy propeller can cause this.

If this is also accompanied by thick brown gunge and you have an old MD engine then it means more but need confirmation..

Meanwhile operate at the throttle settings where the exhaust is clean.

Might be worth checking the prop shaft revolves freely when in neutral.


John
 
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