Why Sailboat Diesels Go Bad

Even if you put Biobor or any other fuel stabilization product into a sailboat’s diesel tank, after a year or so the fuel loses its "caloric oomph." This according to George, the Canadian guy on the powerboat Black Magic 1 from Montreal, which is rafted up next to the Wanderer’s Majestic Dalat at the Arsenal Marina in Paris.

George, who is a very fit and active 71, knows about engines, because although he spent a career working for the Canadian Highway Department, he also had a marine repair business. He had 600 clients.

In his spare time and for free — "I don’t want to be under any obligations" — he now removes/repairs diesel engines and transmissions on canal boats in Europe.

How long does it take to rebuild a diesel?

"It depends on the size, but it takes me about seven hours of labor," he says. "But if you consider the time it takes to get the engine out, put it back in, and wait for parts, it takes a total of about three months."

This is why the Wanderer bought a twin-engine canal boat. If one engine crapped out, I’d still have the other engine and the bow thruster, and thus wouldn’t lose an entire season in Europe. It’s like expensive insurance to not lose a season.

Depending on where you get parts, the price of a rebuild can vary significantly. "I rebuilt a transmission last year and spent $600 on parts from the United States," says George. "If I had bought them in France, they would have cost $6,000!"

Let’s get back to why so many sailboat diesels go bad many years/engine hours before their time.

"It’s the fuel," says George. "If you run old fuel that has lost its caloric oomph, as so many sailors do, it wrecks the engine. This is because when you advance the throttle, you are not controlling the amount of fuel that goes into the engine. That’s done by the engine’s governor. When it gets bad fuel, the governor senses that the engine needs more fuel to reach a given rpm, so it sends two or even three times the normal amount of fuel to the engine. The engine can’t burn the extra fuel, so some of it gets into the cylinders and dilutes the engine oil. If you’re lucky, the rings go bad. If you’re not, the engine seizes up. It doesn’t take long to happen either."

So the important thing is to make sure you go through all the fuel in your engine’s tank at least once a season. If you’re not going to burn through it, you need to cut off the fuel supply to the engine, run it out of fuel, then empty and clean the tank and replace all the filters.

If you’re not going to use your boat’s engine for several years for some reason, George says you need to run a combination of kerosene and automatic transmission fluid through the engine. “It gives the inside of the engine a waxy sort of protective coating. This is what diesel engine manufacturers put in the engines after they’ve tested them to make sure they run."

The other diesel engine killer, of course, is running the engine too hot or too cold. A diesel only runs well in a specific temperature range. Given the price of rebuilding or replacing a diesel, it’s smart to take heed.

That’s the lowdown on sailboat engines from aboard two powerboats in Paris.