Black Coolant-Yanmar

[robbieg]

Got a shock earlier in the week when I checked my engine coolant in my Yanmar 3GM30F-it was black or at least dark brown.

I drained it down & found it was all pretty black & in the inside of the header tank (& presumably the rest of the system) were covered in a black greasy slime. The coolant itself is black & seems to have small black particals in it. However no obvious oil floating on top.

The coolant is a 50/50 Texaco mix. Probably been in for 2 years approx. Engine has never overheated, no water in oil & starts & runs ok.Also no coolant loss.

My first thought was that it was oil in coolant but I would expect it to seperate out & float on top. I've done some googling & this suggests that incompatible coolants & or not using distilled water can cause coolant to go black & create slime & wonder if this is what it is.

The less palitable alternative is that the head gaskets gone & combustion by products are getting into the coolant.

Anyone any experience of this & how to check where the problem originates from. Also how do I clean up the black slime in the header tank etc Thanks.

 

[Stemar]

If the head gasket has gone so oil is getting into the water, water will also be getting into the oil. The most likely giveaway is "mayonaise" on the filler cap or breather. As you say, oil in the water would normally separate, so this seems unlikely.

I've never seen this in engine cooling systems (I try to avoid getting such matters, as I'm one of those people who gets the bandaids out at the same time as the spanners /forums/images/graemlins/frown.gif ) I have seen it in central heating systems, though. The cure is an anti-corrosion additive, so I suspect that you're right about incompatible coolant.

There are at least two kinds of antifreeze, so I'd get some radiator flush and run the engine with that for a bit then flush though with a hose until the water comes out clean then refill with the approved type for the engine. If it's really bad, you might need to repeat the flushing.

 

[Guest]

Corrosion inhibitor

Near all Coolant Glycols are mixed with Corrosiopn Inhibitors so that should not be a concern.

The mix of glycol to other constituents might be though. Often coolant will turn light to mid-dark brown on use ... in fact usually within minutes of adding and use. Dark brown to black is unusual.

I would be inclined as Stemar says to flush through the system ... using plain water actually without addition .... Probably doing it 3 times or so ... Pain in the rear - but then again you get rid of the crud. Once you get only light coloured water out after running etc. - change to water + anti-freeze mix as advised.

The slime is probably gunge that has developed and dropped out of the water used ... if you ever take an old header tank of a car etc. - its full of 'orrid brown slime and gunge ... collects over years from the water ...

Another source of gunge - is addition of system sealer ... such as when a small leak - someone throws Radseal in ... which I hope is not the case here ...

 

[philip_stevens]

I assist a plumber on some of his big jobs, and some of the systems we have drained down, have been black - my own system was also black when we drained it to change some radiators.

He believes this is because no corrosion inhibiter has been added to the domestic supply water that has been used to fill the system. I know our system never had inhibiter in it before we did some work, and black watery gunge was drained out of some old radiators.

Perhaps the coolant does not include inhibiter, and the black is the same as domestic system gunge - steel, copper, iron not compatible without an inhibiter?? Just a thought.

 

[duncan]

I had the same thing exactly on my new Yanmar back in 2002 - it's still running and it still does it!

Like you I started with 'oh no it's the CH garket............' until some bright spark pointed out that it was collecting at the bottom not floating at all.

Yanmar agent went off with some and discussed with Barrus to be told that it was residue casting sand reacting with the antifreeze.

I have flushed through but not 'back flushed' and still get it from time to time.

There was another post on this from someone else a year ago too.

Does this make sense?

 

[pampas]

We had the same problem with a 750kw stand by generator Diesel for years until a new Chief arrived and said "dump that lot flush out and fill with a 15% solubul oil solution", we all thought he was nuts,but in practice it cured two problems.

1 the blackening stopped.

2 the water pump lasted for about two years, usual service life for this component in the tropics being about 8 months.

I now have my central heating filled + car Radiator and recomend it to everbody, can be bought at any steel supplier or machine tool shop for about £11/gallon

 

[Aja]

Happened every season with our 2GM20F. Never did any damage.

Relax

Donald

 

[mercman]

Coolant going black is an indication that the coolant was not mixed before it went into the engine....if it is a 50/50 mix it should be done before it goes in.
If you top up with water at any point this can also cause the blackness.
All yanmars we look after we use texaco xlc it is a pinky coolant and premixed. This should be changed every 2 years.