Bukh changing water in header tank

[Thallac]

Hi
Have a dv48, noticed black soot in header tank, took to boat engineer who said could be back flow from exhaust and suggested change water and keep an eye.

I am going to drain and replace any tips, it is freshwater, I think I can do but was not sure if need to bleed and how after refilling

 

[LittleSister]

If it's freshwater (indirect) cooled, you will want an antifreeze solution (which is also provides corrosion resistance, I believe).

It's the seawater that is pumped into the exhaust, not the freshwater, so I can't think how you could have exhaust backflow into the freshwater unless you had a cylinder head gasket leak (or perhaps both backflow of exhaust into the seawater (which would be indicative of some other problems) and perforated cooling tubes in the heat exchanger, which would give rise (sic!) to the contaminated freshwater overflowing.

That's all off the top of my head, so hopefully someone with more practical experience/knowledge will be along soon.

 

[RichardS]

If it's freshwater (indirect) cooled, you will want an antifreeze solution (which is also provides corrosion resistance, I believe).

It's the seawater that is pumped into the exhaust, not the freshwater, so I can't think how you could have exhaust backflow into the freshwater unless you had a cylinder head gasket leak (or perhaps both backflow of exhaust into the seawater (which would be indicative of some other problems) and perforated cooling tubes in the heat exchanger, which would give rise (sic!) to the contaminated freshwater overflowing.

That's all off the top of my head, so hopefully someone with more practical experience/knowledge will be along soon.

I agree with all that. If it really is soot from the exhaust in the freshwater cooling then you have a major problem and I would check for water in the oil.

If the level of both coolant and oil remain constant then I very much doubt that the black stuff is exhaust soot.

Richard

 

[Thallac]

Thanks for your response, I have checked the oil and it is fine, also the levels of oil and coolant have remained the same,l. The actual coolant is okay, it is the inside top of the header tank that has a black soot on and contaminates the coolant.

 

[RichardS]

Thanks for your response, I have checked the oil and it is fine, also the levels of oil and coolant have remained the same,l. The actual coolant is okay, it is the inside top of the header tank that has a black soot on and contaminates the coolant.

I suspect it is fine black iron oxide which looks very much like black carbon. Are you sure that you have good (nominally 50%) concentration of fresh antifreeze rather than just fresh water or fresh water plus old expired antifreeze? LittleSister also covered this point very well.

Richard

 

[Thallac]

I suspect it is fine black iron oxide which looks very much like black carbon. Are you sure that you have good (nominally 50%) concentration of fresh antifreeze rather than just fresh water or fresh water plus old expired antifreeze? LittleSister also covered this point very well.

Richard

 

[Thallac]

Hi Richard
Is fine black iron oxide, good or bad?
I have not changed antifreeze for 18 months
I plan to flush it out tonight and add new antifreeze
Thanks
Tim

 

[vyv_cox]

Hi Richard
Is fine black iron oxide, good or bad?
I have not changed antifreeze for 18 months
I plan to flush it out tonight and add new antifreeze
Thanks
Tim

Black hydrated iron oxide is theoretically better than the red version as it is the final oxidation stage, Fe3O4OH as opposed to Fe2O3OH. However, neither is good. Well worth changing your antifreeze for a ready use version. Nowadays using tap water to dilute concentrated stuff is frowned upon.

 

[RichardS]

Black hydrated iron oxide is theoretically better than the red version as it is the final oxidation stage, Fe3O4OH as opposed to Fe2O3OH. However, neither is good. Well worth changing your antifreeze for a ready use version. Nowadays using tap water to dilute concentrated stuff is frowned upon.

+1

I use tap water if I know it is soft water but I have a test kit to check. The marinas I use in the Adriatic and Ionian usually seem to be hard or very hard water so I wouldn't use that. If you're in doubt I would follow Vyv's advice.

Richard

 

[Thallac]

+1

I use tap water if I know it is soft water but I have a test kit to check. The marinas I use in the Adriatic and Ionian usually seem to be hard or very hard water so I wouldn't use that. If you're in doubt I would follow Vyv's advice.

Richard

 

[Thallac]

Hi All,

Thanks for your advice. I am on a mooring in the middle of the tidal Thames with no access to water or power. I have drained the engine, cleaned with a radiator cleaner, flushed again (using water from my water tank) and added antifreeze (which i mixed myself). It cleaned the tank and removed the black. I need to run the engine and go for a journey to see if it reappears. When i get the time i will follow your advice and use premixed antifreeze

 

[Malish]

It is possible to buy head gasket tester kits which (I guess) test for abnormally high levels of CO2 in the radiator water - that would at least confirm your carbon theory.

Should have added - if you have a smear of the black material on a clean piece of paper then I can probably tell you what it is via a quick bit of lab work (foc) send me a pm if interested.

 

[Thallac]

Thanks for the kind offer, i will not be on the boat now until September, but will take you up on your offer, if i need to Thanks