Ask SAIL: Smoking Diesel Engine

Author:
Publish date:

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

Calder-head-250x300_1

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

MHS-GMR_3549

New Multihulls 2018

Farrier F-22 New Zealander Ian Farrier ushered in a new genre of sailing with his folding-ama trailerable trimarans, the best-known of which are the Corsair designs. Farrier’s last project before he passed away last year was this sweet little tri. Available in three versions, ...read more

shutterstock_373701682

Cruising: Island Comeback

The U.S. Virgins Islands have surged back from the devastation of the 2017 hurricanes, with new infrastructure plans that will benefit charterers and cruisers alike. After hurricanes Irma and Maria roared through the Leeward Islands in September 2017, it was impossible to ...read more

albintoilet

Gear: Albin Pump Marine Toilet

Head Start Is there room for a new marine toilet? Albin Pump Marine thinks so, having just introduced its line of Swedish-built heads—ranging from compact to full-size models—to the American market. The toilets feature vitreous porcelain bowls and either wooden or thermoplastic ...read more

07n_45R2699

Multihull Sailor: Classic Cats

If you’re looking for a decent sub-40ft cruising cat, you have few choices when it comes to new-boat offerings. It is a well-known fact that the multihull market has taken off in a way very few could have predicted. Despite Hurricane Irma’s recent destruction of a large part of ...read more

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell. Got a tip? Send it to sailmail@sailmagazine.com Thanks a bunch  This scene is very calm and seamanlike. No frantic rope throwing or shouting. As he passes the line to the gent on the dock, the crew on the boat says, quietly and clearly, “Would you ...read more

mcarthy-and-mouse

Experience: McCarthy and the Mouse

Sitting at the helm in a light breeze, my arms crusted with a fine rime of salt, my skin so dry I’d lost my fingerprints, I heard a clatter and a curse from below. There were only three of us a thousand miles from shore and only one on watch at a time. Usually, the off watch lay ...read more