Skip to main content

Ask SAIL: Smoking Diesel Engine

SMOKING DIESEL

Q: I have noticed black smoke from my diesel under high rpm, over 2,000, and suspect unburned fuel to be the cause. I have checked the air intake and fuel filler gauge, made sure of good flow from the exhaust and use a bio-additive in my fuel. The oil level has not dropped. The engine starts and runs normally except for the black smoke. When I back off the throttle the exhaust clears. The engine is an 11hp Universal. Is it possible a dirty prop is the cause?

John Iannacone, via sailmail@sailmagazine.com

NIGEL CALDER REPLIES

Black smoke at higher engine loads is quite common with older engines, especially when accelerating. Unless there is some kind of injector failure, which I doubt in this case, it is the result of excess fuel entering the combustion chamber and not being fully burned. The most likely causes are either overloading, to which the engine’s governor responds by pumping in more fuel than can be burned, or some kind of an obstruction in the air and exhaust flow through the engine.

If it’s the first scenario and you have a foul propeller, you would see a substantial reduction in boat speed for a given engine speed. However, you could have a rope or something wrapped around the propeller shaft that might overload the engine without affecting boat speed much.

As to the second scenario, you say you have checked the air inlet and exhaust, but you may need to look more closely. On older engines, especially on sailboats where engines run long hours at light loads, an exhaust can become fouled up with carbon deposits. Break the exhaust hoses loose to see if this is the case. While you’re at it, see if there are any other potential obstructions in the exhaust system. For example, older hoses sometimes soften and partially collapse, or there may be a kink in the hose.

Nigel Calder is an author and expert on boat systems and diesel engines

Do you have a question for our experts? Submit it to sailmail@sailmagazine.com

September 2015

Related

00-LEAD-JB13-RT1169

What's it Like to Sail a Legend?

At 110 years old, the storied pilot cutter Jolie Brise powers off the wind.  In 1851, the New York pilot schooner America sailed to England, beat the Brits at their own prestigious yacht race (which came to be known as the America’s Cup), and launched an evolution of the East ...read more

Alexforbes Archangel1-1 (14)

Cape2Rio Draws to a Close

With just four boats still on their way, it has been a long road to Rio for the fleet competing in this year’s Cape2Rio. Larry Folsom’s American-flagged Balance 526 Nohri took line honors and a win in the MORCA fleet, finishing with a corrected time of 18 days, 20 hours, and 42 ...read more

_01-Steve-and-Irene-1

Close Encounters: A Star to Steer By

I first met Steve and Irene Macek in the proper way—in an anchorage full of bluewater cruising boats. This was in St. Georges, Bermuda, in the spring of 2019. Theirs, without doubt, was the most distinctive boat there—an immaculate, three-masted, double-ended Marco Polo schooner ...read more

14_01_230123_TOR_JOF_0414-2048x

The Ocean Race Leg 2 Kicks Off

After a trial by fire start to the race and only a brief stop for limited fixes, the five IMOCA 60 crews in The Ocean Race set off for Cape Town, South Africa, early on January 25. Despite arriving somewhat battered in Cabo Verde, an African island nation west of Senegal, the ...read more

Lead

Cruising: Smitten with a Wooden Boat

I was sailing down the inner channel of Marina del Rey under a beautiful red sunset when Nills, one of the crew members on my boat, pointed out an unusual and unique-looking 40-foot gaff-rigged wooden cutter tied to the end of a dock. Its classic appearance was a stark contrast ...read more

Screen-Shot-2023-01-23-at-12.03.19-PM

Racing Recap: Leg One of The Ocean Race

New to spectating The Ocean Race? Managing Editor Lydia Mullan breaks down everything you need to know to get started. ...read more

image00001

From the Editor: Keeping the Hands in Hands-On

SAIL Editor-in-Chief Wendy Mitman Clarke enjoys a sunny autumn cruise in her Peterson 34 on the Chesapeake Bay. It was late afternoon just after the U.S. Sailboat Show in Annapolis when I climbed aboard the last boat on the schedule. I and others who review and sail boats for ...read more

P1580711

B&G Announces New Zeus S Chartplotter

B&G has long been putting out top-of-the-line electronics, but the new Zeus S Chartplotter is a new take on the best way to give sailors the exact information they need, when they need it. “So many more people sail shorthanded these days, whether as a couple or when they’re ...read more