FSS Tidbit #4
Marine Engine Exhaust Elbows
This is an informational post from your FSS Vice Commodores /Safety guy / Mast Wedge Inspector on various things that are boat (Friendship Sloop) related.
Television commercials can be really, really annoying. Have you ever experienced the heartbreak of psoriasis? Heart break, give me a break! How about that special touch that can lead to hours of romantic bliss? And what’s with the bath tubs on the beach? I’ve never seen that in Maine (or anywhere else). I’ll have to admit that every now and then a useful thought does result from the mind numbing drivel of today’s commercial messages. One recent occasion was an asthma medication commercial that graphically showed the constriction of the bronchial tubes of the asthma sufferer and the near miraculous relief provided by the advertiser’s obviously superior product. As I am in the middle of rebuilding another small diesel engine it reminded me to check out the exhaust elbow for similar restrictions. Glad I did. There was much more of a restriction than I thought. Of the 2 inches available for the exhaust gasses my exhaust elbow was down to 1 inch. See the pictures below.
I suppose that after 25 years I should expect some carbon buildup but this amount caught me by surprise. A diesel engine, especially a naturally aspirated one, is particularly sensitive to exhaust back-pressure. It will run fairly well at low RPM but becomes very smoky at higher RPMs. This buildup of carbon is usually caused by running the engine at low RPMs for extended periods and never heating it up fully. Diesels like to run at least 80% of their full load capacity. My problem was the result of years of low to mid- range cruising speeds. So, if your engine has been smoking at cruising speed, or won’t get up to full RPM under power it may be time to pull the exhaust elbow apart and see if it needs a congestion remedy. I know that a sand blaster works just fine, but can’t recommend any of the products “as seen on TV”. The tubs on a beach? Guess they’re not for congestion but I wouldn’t know, never tried it!
Bill Whitney is Vice-Commodore of the Friendship Sloop Society and master and owner of GAIVOTA, FSS #214