Wet exhaust water is black

[bmjnyc]

Everyday I'm happier and happier with my new Contessa 26. She is the perfect size and her systems are just complicated enough to allow me to figure out how to fix them while learning about them.

Today I went to pick up my boat which I had put away in a protected inlet in which she could ride out Irene. There was no wind so I had to motor. When I checked the water exhaust in the back of the boat to make sure that the water pump was working I noticed that the water was blackish in color and seemed to have a bit of smoke mixed into it. The more gas I gave the motor the darker the water.

Two weeks ago some jelly fish clogged the fresh water intake for the motors cooling system. As a result my motor quickly overheated, the cabin filled with blue smoke. I checked the motor after this happened and found that my Vetus water lock exhaust had started to melt so that all the wet exhaust was gushing into my bilge.

I bought a new water lock exhaust, installed it. Today was the 4th time I used the motor since the installing the exhaust.

I've know very little about diesel motors but I'm thinking I might need a oil filter. I did change my oil a month ago but did not change the filter.

Has this happened to anybody, any input would be greatly appreciated.


The motor is a 6hp Kubota.

[Faster]

Soot or carbon in your exhaust will have nothing to do with an oil filter, but you should get into the habit of changing your filter every time you change the oil anyway.

Does the engine sound any different? If an injector is getting dirty that might contribute, and if it's bad enough there will be a bit of a ticking sound that goes with it. Generally soot in the exhaust means an engine is working too hard due to over propping, extra drag, or being pushed too hard.

[Sublime]

Sounds like a blown head gasket or possibly a cracked block which is what happens when they overheat. The oil is mixing with the water is a classic sign.

[bmjnyc]

The motor does not sound any different. I'm going to have a mechanic look at it as it seems beyond my abilities to diagnose. Thanks for the the ideas on what to look for.

[DrB]

Keep it super simple. Before you call a mechanic and tear the engine apart, try this. Fire up the motor and leave it idle and neutral and allow it to warm up. With the motor now running warm is the exhaust water black? No, give it full throttle in neutral. No or very little black soot, then your motor is probably okay. Can you get full revs on the motor when in neutral? If yes, your motor is probly okay, look elsewhere such as fouled or bent prop.

DrB

[JimsCAL]

Keep an eye on the lube oil. If it takes on grayish color you have a problem - water in the oil - and will need at least a new head gasket.

[PorFin]

Originally Posted by Sublime

Sounds like a blown head gasket or possibly a cracked block which is what happens when they overheat. The oil is mixing with the water is a classic sign.

Kind of disagree with this one -- blown head gasket or cracked block would have coolant getting into the cylinders, creating steam, leading to a light gray or whitish color in the exhaust.

Blackish colored exhaust usually indicates incomplete ignition of fuel and/or oil that is getting into the cylinders. Blackish colored exhaust water is likely related to carbon build-up in the exhaust system -- usually in the mixing elbow.

[RichH]

Originally Posted by PorFin

Kind of disagree with this one -- blown head gasket or cracked block would have coolant getting into the cylinders, creating steam, leading to a light gray or whitish color in the exhaust.

Blackish colored exhaust usually indicates incomplete ignition of fuel and/or oil that is getting into the cylinders. Blackish colored exhaust water is likely related to carbon build-up in the exhaust system -- usually in the mixing elbow.

Agree with one exception.
A diesel engine will not have relatively complete combustion efficiency until the combustion chamber comes up to full operating temperature. Until the combustion chamber is fully 'heat soaked' you will get a 'sooty exhaust' especially when "applying more throttle" (over-fueling) or attempting to run the engine at higher rpm or load .... until the engine is fully 'warmed up'. Throttling-up a cold internal combustion (diesel or gasoline) engine will actually drop temperature as the 'overabundance' (more than what can be 'burned' vs. the combustion chamber operating temperature) of injected fuel will 'cool' the combustion chamber ... until the engine is at stable operating temperature. Simple thermodynamics of the Diesel or Otto cycle.

Freshwater cooled engines quickly become 'heat soaked' and operate @ near 180°F. Raw water engines take longer to come up to stable operating temperature AND they operate so to keep the exit cooling water at less than 150° hence they run a bit cooler and thus emit more 'black exhaust' when 'over-fueled' by the throttle .

[PorFin]

Originally Posted by RichH

Agree with one exception.
A diesel engine will not have relatively complete combustion efficiency until the combustion chamber comes up to full operating temperature. Until the combustion chamber is fully 'heat soaked' you will get a 'sooty exhaust' especially when "applying more throttle" (over-fueling) or attempting to run the engine at higher rpm or load .... until the engine is fully 'warmed up'. Throttling-up a cold internal combustion (diesel or gasoline) engine will actually drop temperature as the 'overabundance' (more than what can be 'burned' vs. the combustion chamber operating temperature) of injected fuel will 'cool' the combustion chamber ... until the engine is at stable operating temperature. Simple thermodynamics of the Diesel or Otto cycle.

Freshwater cooled engines quickly become 'heat soaked' and operate @ near 180°F. Raw water engines take longer to come up to stable operating temperature AND they operate so to keep the exit cooling water at less than 150° hence they run a bit cooler and thus emit more 'black exhaust' when 'over-fueled' by the throttle .

Rich -- thanks for adding clarity and detail to my incomplete thought!

[casey1999]

Originally Posted by PorFin

Kind of disagree with this one -- blown head gasket or cracked block would have coolant getting into the cylinders, creating steam, leading to a light gray or whitish color in the exhaust.

Blackish colored exhaust usually indicates incomplete ignition of fuel and/or oil that is getting into the cylinders. Blackish colored exhaust water is likely related to carbon build-up in the exhaust system -- usually in the mixing elbow.

My 30 year old 3GMD always has grey/white smoke (trails from exhaust outlet for about 2 feet behind boat them disapears) and does this only after it was warmed up and I have been running it at high rpm. Engine uses no oil and oil color is good (no water mixed in). Would this mean I have a gasket or block problem or could it be somthing else. Engine starts easily and seems to run great, and does not overheat. Could the grey/white smoke just be from the water hitting the exhaust. I am in Hawaii so it is not from cold outside temperatures. I think my fuel is good (new). All filters are new.