Black exhaust water (soot?)

[sandycohen]

I bought a 1979 pearson 32 about three months ago with a Yanmar 2gm20f. Until last week I ran the engine at around 2200 rpm cruising. Then I realized it wants to be run higher and recommended speed is 80 percent of max. So, the last time out I cranked her and all was well. Today went out and after five minutes noticed black stream in the exhaust water (not smoke). It may have been there from go but I didn't notice. When idled down no black. When run under high rpm with no load (neutral) no black. I took a sample of the black water and it is not oil, it's sooty. Engine doesn't seem unusually hot and gas who be fine. Don't know about filters, haven't checked.

Is it possible that the two hours max i ran engine at 2000 cruising over a couple of months built up so much soot in the elbow or muffler that i just need to blow it out by running at high (correct) speed? I didn't persist since black stuff coming out the back the boat freaks one out.

Bottom is clean and i don't think there's a prop issue (it's folding) and there is no rough running, trouble starting, speed fluctuations etc..

Thanks!

 

[Roger Long]

Is it possible...?

More than. Run hard for a while and keep an eye on it. If it's black stuff running out, I wouldn't be concerned if the engine sounds strong and smooth.

Look at the smoke itself. If it is black like you see on a heavy truck pulling away from a stop light, than you might be over propped (rare on a production sailboat) or have a fuel restriction.

Watch for the trend. If the black stuff running out increases in volume and at an increasing rate, more investigation may be warranted.

Due to propeller characteristics, the optimum 80% power band is actually at about 90% RPM. You should look in your manual to see if there is a rating for 1 hour or 10% of operating time and another rating for continuous operation. You want to be running at 80% of continuous.

Oh, don't check your filters. Change them immediately. Change them at the beginning of every season whether you need to or not.

 

[Bill Roosa]

Agree with Roger. don't forget to check the air filter. Roger is a nervous navigator and probably never has a filter that is fully used. I'm some what more acceptable of risk and only change my filters when the manufacturer recommends. I do keep a full set of filters for replacement at sea however.

 

[Roger Long]

only change my filters when the manufacturer recommends.

I think that's every season. In any event, I change them when our resident filter expert, consultant to the people who make the filters among other things, recommends.

What makes you think I'm nervous?

 

[sailaway78]

PROP

My first place to look would be the prop. Either the wrong pitch or some barnacles on it. Just went through a very similar situation, and even though the boat had been recently hauled, and the bottom done, the prop had some barnacles the size of a dime. Cleaned prop, problem solved. I do agree on changing filters. Don't know why some don't do it more often. This is an inexpensive and easy thing to do. Change them at least once a season. Even if you don't think they need it. A partially clogged filter equals only one thing. PROBLEMS